AU615014B2

AU615014B2 - Superconducting thin film and wire and a process for producing the same

Info

Publication number: AU615014B2
Application number: AU27099/88A
Authority: AU
Inventors: Kenjiro Higaki; Hideo Itozaki; Tetsuji Jodai; Saburo Tanaka; Shuji Yazu
Original assignee: Sumitomo Electric Industries Ltd
Current assignee: Sumitomo Electric Industries Ltd
Priority date: 1987-02-17
Filing date: 1988-12-20
Publication date: 1991-09-19
Anticipated expiration: 2008-12-20
Also published as: AU2709988A

Description

4 _.iL :1' COMMONWEALTH OF AUSTRAL 1 4 Patents Act 1952 CO M P L E T E S P E C IF I C ATION

(ORIGINAL)

Application Number Lodged Complete Specification Lodged Accepted Published 1 Priority S Related Art Name of Applicant Address of Applicant Actual Inventor/s Address for Service ao~ter 1987, 22 IcsrPer 1987, 22 Dotrer 1987, 22 Daaster 1987, 22 ecarner 1987, 22 1~rnter 1987, 22 DFeraer 1987, 22 Coarer 1987, 22 Darser 1987, 22 Diec3 er 1987, 22 DIoater 1987, 29 DaI~ er 1987, 22 January 1988, 22 Ja~anry 1988, 22 Janary 1988, 22 January 1988, 22 January 1988.

:SUMITOMO ELECTRIC INDUSTRIES, LTD.

:15, Kitahama 5-chome, Higashi-ku, Osaka, 541 Japan :Saburo TANAKA, Hideo ITOZAKI, Kenjiro HIGAKI, Shuji YAZU Tetsuji JODAI, F.B. RICE CO.

Patent Attorneys 28A Montague Street, Balmain N.S.W. 2041 Complete Specification for the invention entitled: Superconducting thin film and wire and a process for producing the same The following statement is a full description of this invention including the best method of performing it known to us/me:i ML i L_ Xe~ Background of the Invention Field of the invention The present invention relates to a superconducting thin film and a process for producing the same. More particularly, it relates to a superconducting thin film having improved high current density of oO°: superconductivity and a process for producing the same.

The superconducting thin film according to the present invention ol possesses improved surface flatness as well as high critical temperature and high current density and is advantageously applicable in a variety of 'to, electronics devices including the integrated circuits.

The present invention also relates to a superconducting wire and a process for producing the same. More particularly, it relates to a S.superconducting wire having improved high current density of Ssuperconductivity and a process for producing the same.

SThe superconducting wire according to the present invention is advantageously applicable in the field of electric power transportation and q o,.o in a variety of wiring materials for electronics devices. Description of the related art The superconductivity is a phenomenon which is explained to be a kind of phase changes of electrons under which the electric resistance become zero and the perfect diamagnetism is observed.

-1 ai In the field of electronics, a variety of superconducting devices are known. A typical application of the superconducting device is Josephson device in which quantum efficiency is observed macroscopically when an electric current is passed through a weak junction arranged between two superconductors.

The tunnel junction type Josephson device is expected to be a highspeed and low-power consuming switching device owing to smaller energy gap of the superconducting material. It is also expected to utilize the Josephson device as a high sensitive sensor or detector for sensing io very weak magnetic field, microwave, radiant ray or the like since 4 variation of electromagnetic wave or magnetic field is reflected in 6° variation of Josephson effect and can be observed as a precise quantum ~phenomenon. Development of the superconducting devices such as high- 4 speed logic units or no power-loss wiring materials is also demanded in the field of high-speed computers in which the power consumption per unit area is reaching to the upper limit of the cooling capacity with increment of the integration density in order to reduce energy consumption.

The superconducting wire is demanded in the field of electromagnetic coils or a variety of electric parts as well as in the field of electric power transportation. For example,in the high-speed computers, the superconducting wires is demanded as a wiring material for IC 14 Q packaging or the like for delivering current without any loss of power.

However, the critical temperature "Tc" of superconductivity could not exceed 23.2 K of Nb3Ge which was the the highest Tc for the past ten years.

1 The possibility of an existence of a new type of superconducting material having much higher Tc was revealed by Bednorz and Mtiller, who discovered a new oxide type superconductor in 1986 Phys. B64 (1986) 189].

The new type compound oxide superconductor discovered by Bednorz and MUller is represented by [La, Sr]2CuO4 which is called the K2NiF4-type oxide having a crystal structure which is similar to known perovskite type oxides. The K2NiF4-type compound oxides show such higher Tc as 30 K which are extremely higher than known superconducting materials.

It was also reported that C. W. Chu et al. discovered, in the United States of America, another superconducting material so called YBCO type represented by YBa 2 Cu307-x having the critical temperature of about K in February 1987. And hence, the possibility of an existence of hightemperature superconductors have burst onto the scene.

It is said that the superconducting properties of the abovementioned new type compound oxide superconductors are influenced by o the oxygen deficiency in the crystal. In fact, if the oxygen deficiency do not exist in the crystal, Tc can not be higher and a discrepancy between S2"6 the on-set temperature and a temperature where perfect zero resistance is observed become big.

S° Generally, the thin films composed of the above-mentioned new type superconducting materials are prepared by physical vapour j deposition technique. However, the critical current density "Jc" observed in the superconducting thin film obtained is very low even if the thin film possesses a high critical temperature Such low critical current i i '0

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density is a problem when the thin films are utilized as superconductors in practical uses.

The superconducting wires composed of the compound oxides are generally produced by a wire-drawing technique in which sintered powder material of the compound oxide is compacted in a metallic sheath which is then drawn. In the superconducting wires produced by the conventional technique, however, it is difficult to improve the critical current density even if the superconducting wire shows a high critical temperature Tc. In fact, since the compound oxide is an anisotropic o crystal in which electric current flow mainly along its c-axis, the S°:0 maximum current density of the conventional superconducting wire whict S is produced by the conventional technique in which powders of such 0 compound oxide is compacted at random is limited to a value which is insufficient to use the wire in practical uses.

a In the conventional sputtering technique for preparing a thin film composed of the ceramics type oxide superconductors disclosed in Japanese patent laid-open No. 56-10,9824, sputtering is effected in oxygen-containing atmosphere while the substrate is heated in order to improve ordering or orientation of the crystal and the resulting film o2d deposited on the substrate by the sputtering stage is further heat-treated in order to increase the oxygen-content in the thin film.

This patent teaches that the superconducting thin fihn which is represented by the formula BaPbl-xBixO3 (in which 0.05 x 0.35) and which is prepared in an oxygen-containing atmosphere by highfrequency sputtering technique should be further heat-treated at 500 to 550 'C but mentions nothing about the conditions how to prepare the thin t -4- 0 gj 1, film of high-Tn superconductor which was discovered after the filing date of this patent.

The present applicant has already proposed several processes for preparing the thin films of the high-Tc superconductor including US patent No. 4900716 and US i patent No. 4996185.

Although the processes disclosed in these patents are themselves useful and satisfactory, it is still requested to improve further the critical temperature and particularly the critical current density. The present invention is an extension of and an improvement in these patents.

Therefore an object of the present invention is to provide an improved thin film which is composed of compound oxide type superconducting material and which has a high critical density of superconductivity in addition to the high critical temperature and a process for producing the same.

Another object of the present invention is to solve 20 the above mentioned problem and to provide an improved compound oxide type superconducting wire having higher S current density.

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I. \1 5a Summary of the Invention In a first aspect the present invention comprises a superconducting composite consisting of a substrate and a superconducting thin film which is deposited on said substrate and which comprises superconducting compound oxide whose critical temperature is higher than 28K, wherein a substantial portion of the surface of said superconducting thin film has a smooth surface having a surface roughness of Rmax (datum length=1,000pm) of less than 0.2pm.

In a second aspect the present invention comprises a superconducting wire comprising a core and a superconducting thin film which comprises superconducting compound oxide whose critical temperature is higher than 15 28K and which is deposited on a surface of said core by physical vapour deposition technique, wherein a substantial portion of the surface of said superconducting thin film has a smooth surface having a surface roughness of Rmax (datum length 1,000 pm) of less than 0.2 pm.

Se 00 0a 04 L oI mainly o ound oxide, characterized in that the substantial portion of a surface of the supe ducting thin film is smooth.

The second subject er of the present invention is a superconducting wire consisting of a core a superconducting thin film which is deposited on the core and which is c osed mainly of compound oxide, characterized in that the substantial portio n o uface of the suer eond cting thin film is oth.

The expression of "the substantial portion mean that the majority, for example more than 80 of the surface of the superconducting thin film is smooth even if voids or defects which are inevitably produced when a thin film is deposited on a large area by the physical vapour deposition technique are observed in the remaining minor portion of the surface.

The smoothness of the superconducting thin film is evaluated by such a fact that the surface roughness Rmax (datum length 1,000pm) of lthe superconducting thin film composed mainly of compound oxide is less than 0.2 The value of the surface roughness Rmax is determined by observing the thin film obtained microscopically, particularly by SEM.

Experiments which were conducted by the present inventors revealed such a fact that the critical current density "Jc" observed on the thin film obtained decrease sharply if the surface roughness Rmax is not less than 0.2 jim.

The superconducting thin film according to the present invention is composed mainly of compound oxide represented by the following general formula and -6- 26 A xeiet hc wr odce yte rsn netr LnlBa2Cu307-8 in which "Ln" stands for at least one lanthanide element selected from a group comprising La, Nd, Sm, Eu, Gd, Dy, Ho, Y, Er, Yb, Tm and 8 is a number which satisfies a range of 0 1.

The "Ln" is preferably Y, Er, Ho or Dy. The compound oxide is considered to be consisted mainly of perovskite type or quasi-perovskite type oxide.

An atomic ratio of the lanthanide element "Ln" Ba Cu is preferably 1 2: 3 as is defined by the formula but the atomic ratio is not restricted strictly to this ratio. In fact, the other compositions whose atomic ratio deviate from the above-mentioned value by 50 more o o preferably by 20 can be inciaded in the scope of the present invention.

The expression of "composed mainly of" defined in Claims means that compound oxides whose atomic ratio of Ln Ba Cu is not equal to 1 2: 3 are also included in the scope of the present invention.

This definition means also that the compound oxide can contain 4 impurities which exist inevitably at the concentration of ppm order as well as another component which is added intentionally in order to improve the other properties of the thin film obtained.

94 3 2V As the components added intentionally, it can be mentioned Sr, Ca, Mg or Be of the IIa group of the periodic table and an element which is selected from elements of IIIa, Ib, IIb, IIIb, IVa and VIIIa groups of the periodic table such as Ti, V but which is not the elements contained in the formula.

(Lal-xax)2CuO4 in which a stands for Ba or Sr and 0< x< 1.

The compound oxide is considered to be consisted mainly of perovskite type or quasi-perovskite type oxide. It is preferable that an atomic ratio of La Ba (or Sr) Cu satisfies the value defined by the formula but the atomic ratio is not restricted strictly to the ratio. In fact, it is often observed that the other compositions whose atomic ratio deviate from the above-mentioned ratio by 50 more preferably by 20 also show effective superconducting property. Therefore, the expression of "composed mainly of'" defined in Claims means that compound oxides whose atomic ratio are not equal to the value defined by the formula are also included in the scope of the present invention.

II This definition means also that the compound oxide can contain S impurities which exist inevitably at the concentration of ppm order as well as another component which is added intentionally in order to improve the other properties of the thin film obtained.

As the components which can be added intentionally, it may be mentioned Sr, Ca, Mg or Be of IIa group of the periodic table and an S element selected from elements of IIa, Ib, IIb, IIIb, 1Va and VIa groups of the periodic table such as Ti, V which are not the elements contained in the formula.

In the case of the superconducting thin film which is the first subject matter of the present invention, the substrate on which the superconducting thin film of compound oxide is deposited can be a substrate made of perovskite type crystal or oxide, or a substrate made of metal or semiconductor on which a buffer layer composed of perovskite type crystal or oxide is deposited. The substrate is preferably made of single crystal of MgO, SrTiO 3 ZrO2, YSZ or A1 2 03, polycrystal of -8- V -"J A1 2 03 or made of metal or semiconductor having a buffer layer made of these materials and having a deposition surface on which the superconducting thin film is deposited. The thin film is preferably deposited on a (001) plane or (110} plane of the substrate made of a single crystal of MgO or SrTiO 3 In the case of the superconducting wire which is the second subject matter of the present invention, the core can be a core male of metal or ceramics or a core made of metal having a buffer layer composed of ceramics. The metals for the core are preferably platinum metals, particularly Pt, Ag, Au and their alloys but are not limited thereto. The S diameter of the metal wire should be as finer as possible and is preferably less than 1 mm. The ceramics for the core are preferably oxides or compound oxides which are preferably single crystals or polycrystals but Scan be also glass. When the ceramic of a single crystal or polycrystal is used, the ceramics are preferably selected from those whose lattice distance is nearly same as the lattice distance of the crystal of the compound oxide to be deposited and are preferably selected from be 0 MgO, SrTiO 3 and ZrO2. The ceramics have preferably {001) plane or 4 0 (110} plane so that the superconducting thin film of compound oxide is 26° grown along c-axis.

thivd-subjeet-mtte--ef-ho prent invntion i pe es fo producing the sup ducting composite and the superconducting wire.

SThe processes for proi a superconducting composite or superconducting wire according to the p t invention include a physical vapour deposition stage for depositing a super ucting thin filyfl on a substrate or on a earc H 1 -9 -Li I' 9a In a third aspect, the present invention comprises a process for producing a superconducting wire comprising a core and a superconducting thin film which comprises superconducting compound oxide whose critical temperature is higher than 28K and which is deposited on a surface of said core by physical vapour deposition technique, wherein the physical vapour deposition is carried out in such a manner that a substantial portion of the surface of said superconducting thin film obtained finally has a smooth surface having a surface roughness of Rmax (datum length S 1,000 pm) of less than 0.2 pm by controlling operational conditions during the physical vapour deposition.

The processes for producing a superconducting composite or superconducting wire according to the present invention include a physical vapour deposition stage for depositing a superconducting thin film composed mainly of compound oxide on a substrate or on a core, and i 040440 IA e,/ otL ur 1 0 are characterized in that the physical vapour deposition is carried out under such an operational condition that the substantial portion of a surface of the superconducting thin film obtained finally become smooth by controlling at least one of parameters selected from a group comprising a deposition rate, atmosphere gas pressure, oxygen gas contents and high-frequency power.

The conditions of to are described hereafter in more details.

The superconducting thin films composed of compound oxides obtained by the processes according to the present invention are thin films lo composed mainly of the following compound oxides and (2) 4 LnlBa2Cu37-86 (1) S0 o (Lal-xXxc) 2 CuO4 (2) The details of these compound oxides are already described in the S first and second subject matters of the present invention and hence are not repeated here.

At first, we will describe the physical vapour deposition technique on which the processes according to the present invention based.

According to the present invention, sputtering technique, more preferably RF (radio frequency) sputtering technique which itself is well- 26 known is used in the physical vapour deposition. In the physical vapour deposition technique, an atomic ratio of metal elements contained in a vapour source is adjusted according to difference in the evaporation rate as well as in the deposition possibility of each metal element. The vapour source is preferably constructed of a sintered mass which is prepared by powder sintering technique of material power mixture comprising metal elements and/or their oxides or carbonates and whose atomic ratio of the

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Vt 4i 4 ItQ a a I laur 4Q 0 t r o 4o 4 4 4 2 6' 4 4 4 metal elements is adjusted according to respective vaporization rates of the metal elements, or is constructed of a sintered powder which is obtained by pulverizing the sintered mass. The vapour source may consist of a plurality of segments each selected from powders of constituent metal elements, oxide or carbonate such as powders of Y203, CuO and BaCuO2.

For example, the vapour source can consist of two segments of elemental Cu powder and a compound oxide of Ba and Y.

The substrate on which the superconducting thin film of compound oxide is deposited is preferably a single crystal whose lattice distance is nearly same as the lattice distance of the crystal of the compound oxide such as a single crystal of MgO, SrTiO3 or ZrO2. The deposition surface is preferably (001) plane or [110} plane of the single crystal of MgO or SrTi0 3 In the case of the superconducting wire, the core can be a metal wire or ceramic wire or a metal wire having a thin buffer layer composed of ceramics. The metals for the core are preferably platinum metals, particularly Pt, Ag, Au and their alloys but are not limited thereto. The diameter of the metal wire should be as finer as possible and is preferably less than 1 mm. The ceramics for the core or for the thin buffer layer are preferably oxides or compound oxides which are preferably single crystals or polycrystals but can be also glass. When the ceramic of a single crystal or polycrystal is used, the ceramics are preferably selected from those whose lattice distance is nearly same as the lattice distance of the crystal of the compound oxide and are preferably selected from MgO, SrTiO3 and ZrO2. The ceramics have preferably {001 plane or 1101 -11-

L_

4.

plane so that the superconducting thin film of compound oxide is grown along c-axis.

According to a preferred embodiment, the substrate or the core is heated during the sputtering stage. The heating temperature for the substrate or the core is 200 to 950 preferably 500 to 920 If the temperature of the substrate or core is not higher than 200 the deposited compound oxide do not possess proper crystalline structure but become glass and hence do not show superconducting property. To the contrary, if the temperature of the substrate or core exceed 950 'C, another crystalline structure which does not show superconducting property is produced in the deposited compound oxide.

Now, we will describe the above-mentioned sputtering conditions i to These conditions to are deternmined from different points of view on the present invention and have respective ranges defined hereafter. In the present invention, each of the conditions can be selected solely or more than two conditions selected from these conditions can be combined with each other.

4, Deposition rate The deposition rate which is defined according to the first aspect of 26. the present invention must be within a range of 0.05 to 1 A/lsec, preferably within a range of 0.1 to 0.8 A/sec. Experiments which were 4 conducted by the present-inventors revealed such a fact that, if the deposition rate during the physical vapour deposition exceed 1 A/sec, the critical current density observed in the superconducting thin film obtained deteriorate sharply, so that such superconducting thin film can not be used in practical uses. To the contrary, if the deposition rate during the -12physical vapour deposition is not higher than 0.05 A/sec, the deposition speed become too much slow to perform the deposition in the industrial scale.

Atmosphere gas pressure The atmosphere gas pressure which is defined according to the second aspect of the present invention must be within a range of 0.001 to Torr, preferably within a range of 0.01 to 0.3 Torr.

Oxygen gas contents In the present invention, a mixed gas consisting of inert gas and oxygen is selected as the atmosphere gas in the sputtering stage. The S proportion of oxygen or the oxygen contents in the mixed gas which is defined according to the third aspect of the present invention must be within a range of 5 to 95 preferably within a range of 10 to 80 The inert gas or sputtering gas which can be mixed with oxygen is preferably argon.

High-frequency power In the present invention, the sputtering is preferably performed by RF (radio frequency) magnetron sputtering technique. The highfrequency power applied during the sputtering stage which is defined 206 according to the forth aspect of the present invention must be within a range of 5 to 200 W with respect to a target having a diameter of 10 cm, that is 0.064 to 2.55 W/cm 2 f When the oxygen contents in the sputtering gas is low, the highfrequency power is also reduced relatively to a range of 5 to 100 W with respect to a target having a diameter of 10 cm, that is 0.064 to 1.27 W/cm 2 To the contrary, if the oxygen contents in the sputtering gas is -13higher than 30 to 95 by molecule, particularly 40 to 80 by molecule, the high-frequency power is preferably increased to a range of 1.27 to 2.55 W/cm 2 According to the processes of the present invention, the sputtering is carried out under such a condition that the the substantial portion of a surface of said superconducting thin film becomes smooth.

The smoothness of the superconducting thin film obtained is evaluated by such a fact that the surface roughness Rmax (datum length 1,000)tm) of the superconducting thin film composed mainly of compound oxide is less than 0.2 tm. The value of the surface roughness 0' Rmax is determined by observing the thin film obtained microscopically, particularly by SEM.

part According to a preferred embodiment of the processes of the present invention, after deposition of the thin film complete, the resulting thin film is further heat-treated or annealed in an oxygen-containing atmosphere and then is cooled slowly. The heat-treatment is preferably carried out at a temperature ranging 800 to 960 °C and the cooling rate of 4 4 0 the thin film is preferably less than 10 °C/min. The heat-treatment is preferably carried out at a partial oxygen pressure ranging 0.1 to 10 atm.

The purpose of the heat-treatment is to adjust the oxygen deficiency in the compound oxide. In fact, the thin film which is not subjected to the heat- 0 treated often shows poor superconducting property and in the worst case .i does not exhibit superconducting property. Therefore, the heat-treatment is preferable.

The superconducting thin film of the above-mentioned type compound oxides shows anisotropy in the critical current density. V 14- Namely, the current passing along a direction which is in parallel with a plane defined by a-axis and b-axis of the crystal show a very high critical current density, while the current passing along the other directions is relatively lower. Therefore, in order to accord the crystalline orientation of the superconducting thin film with that of the substrate, it is a general practice to deposit the superconducting thin film on the specified plane of a single crystal such as MgO, SrTiO 3 YSZ, ZrO2 or the like whose lattice distance is nearly same as the lattice distance of the compound oxide crystal. However, the maximum critical current density "Jc" of the 1o conventional processes have been limited to a rather low value of 1 x 105 A/cm 2 because the orientation of crystal could not ordered satisfactorily.

The advantage of the processes according to the present invention S.reside in that the critical current density "Jc" of the superconducting thin film can be increased at one effort to the level of 1 x 106 A/cm 2 which is one order higher than the conventional value. Such great improvement in the critical current density result from such a fact that the surface roughness of the superconducting thin film of compound oxide is improved by adjusting at least one of the conditions to to the 4 optimum value.

Although the theoretical reason why such important improvement in the current density "Jc" can be achieved by the improvement in the a a surface roughness is not clear under the present situation, we think that S the improvement in the current density "Jc" may come from such a reason that the direction of crystalline orientation of c-axis in the superconducting thin film prepared by the present invention is ordered perpendicularly or nearly perpendicularly with respect to a surface of the

A,

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substrate or the core. Therefore, it is preferable to deposit the 11 superconducting thin film on [001 plane of a single crystal of MgO or SrTiO3. It is also possible to use [110} plane. In this case, the c-axis become in parallel with a surface of a substrate, so that current is flown perpendicularly with respect to the c-axis in the practical uses. Still more, since the thermal expansion coefficient of MgO or SrTiO3 is similar to that of the superconductor of compound oxide, the thin film is not subjected to undesirable stress caused by difference in the thermal expansion coefficient which will be exerted during the heating and cooling 1o stages.

In conclusion, the superconducting thin film obtained by the process S according to the present invention exhibit very higher critical current density than those that are prepared by the conventional processes.

Now, several embodiments of the processes for producing the superconducting composites and superconducting wires according to the present invention will be described by Examples, but the scope of the present invention should not be limited thereto.

The experiments shown in the following Examples were conducted for the purpose of determining the optimum ranges for each of the o conditions to with respect to LnlBa2Cu3O7-8 type superconductors and (Lal-xcx)2CuO4 type superconductors.

S0 i In the Examples, the critical temperature of superconductivity (Tc) is determined by the conventional four probe method. The critical current density (Jc) is determined at 77.0 K and is expressed by A/cm 2 Namely, electric resistance is measured with increasing the amount of

V

r current and a value of the current intensity where resistance detected at first is divided by a cross sectional area through which current pass.

The value of the surface roughness Rmax is determined by taking a photo of the thin film deposited by SEM (Scanning Electron Microscopy).

Ln1Ba2Cu3Q7-5 type superconducting thin films Example 1 Superconducting thin films are prepared by RF magnetron sputtering technique. Targets used in the Examples are compound oxides of Ln-Ba-Cu-O ceramics each having an atomic i-atio of Ln Ba Cu 1 0 2.24 4.35. "Ln" stands for lanthanide elements shown in Table 1. Each targets has a disk-shape having a diameter of 100 mm. The sputtering is carried out under same operational conditions for all samples. The operational conditions are as following: 4 0 :Substrate: MgO {0011 plane Atmosphere gas: 02/(02+Ar) Atmosphere gas pressure: 0.1 Torr a. Substrate temperature: 700 °C o High-frequency power: 40 W (0.51 W/cm 2 o Sputtering time: 6 hours Thickness of the thin film: 0.88 in ,(Deposition rate 0.35 A/sec) After the deposition complete, the resulting thin film deposited on the substrate is heated at 900 'C for three hours and then cooled to ambient temperature at a cooling rate of 5 °C/min.

1 -17- ifiL 4 1 a 4 230 4 44 4 4 The critical temperature and the critical current density observed on the resulting thin films are summarized in Table 1.

As comparative examples, sputtering is carried out under the same conditions as above except that the high-frequency power is increase to 150 W (1.9 W/cm 2 The results are also shown in Table 1.

Table 1 Ln Critical temperature Critical current density Tc Jc (A/cm 2 Comparative Ho 82.0 850 Tm 82.0 850 Lu 82.0 845 Present Ho 82.1 2.0 x 106 invention Er 86.0 2.5 x 106 Y 81.0 1.5 x 10 6 Dy 83.2 2.5 x 106 Gd 81.0 1.7 x 10 6 Eu 80.6 1.2 x 106 Sm 80.4 1.0 x 106 Yb 80.2 1.0 x 106 Nd 80.8 1.2 x 106 La 79.0 0.8 x 106 Tm 82.1 1.8 x 106 Lu 80.4 1.0 x 106 It is apparent from the results shown in Table 1, the superconducting thin films prepared in the condition defined by the present invention exhibit much higher critical current density than the comparative examples.

-18- ,4 I 4 1 4 r I L i -6- 'd4

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From such a fact that we can not find any unevenness on the surfaces of the thin films of compound oxides obtained by thz present invention when the surfaces are observed by SEM at 10,000 magnifications, while there exist grains of several microns on the surfaces of the thin films obtained by the comparative examples, we can estimate that the structure of the superconducting thin films of compound oxides obtained by the process according to the present invention is uniform and compacted Example 2 Superconducting thin films are prepared by RF magnetron .sputtering technique. Targets used in the Examples are ceramics of S compound oxides of Ln-Ba-Cu-O which are prepared by usual sintering 'technique in which material pcwders whose atomic ratio of Ln Ba Cu is adjusted to 1 2.24 4.35 is sintered. "Ln" stands for lanthanide elements shown in Table 2. Each targets has a disk-shape having a diameter of 100 mm. The sputtering is carried out under the identical S operational conditions for all samples. The operational conditions are as following: Substrate: MgO (001} plane Substrate temperature: 700 °C Atmosphere gas: 02/(02+Ar) Atmosphere gas pressure: 0.1 Torr High-frequency power: 40 W (0.51 W/cm 2 Sputtering time: 6 hours Thickness of the thin film: 0.88 p-m -19- 4/ (Deposition rate 0.35 A/sec) After the deposition complete, the resulting thin film. deposited on the substrate is heated in 02 of atmospheric pressure at 900 °C for one hour and then cooled to ambient temperature at a cooling rate of C/rmin. The critical temperature and the critical current density observed on the resulting thin films are summarized in Table 2.

As comparative examples, sputtering is carried out under the same conditions as above except that the deposition rate is increase to 1.5 A/sec.

The results are also shown in Table 2.

Table 2 Ln Critical temperature Critical current density Tc Jc (A/cm 2 Comparative Ho 82.0 850 Tm 82.0 850 Lu 80.0 840 o 4 4 o 0 o a d 4 0 tt Present invention o 44 Q4 440 0 Ho Er

Y

Dy Gdd Eu Sm Yb Nd La Tm Lu 82.2 87.1 80.5 83.1 81.2 80.5 80.0 80.0 80.4 79.3 82.2 80.5 1.9 x 2.8 x 1.4 x 2.6 x 1.8 x 1.1 x 0.9 x 0.9 x 1.1 x 0.8 x 1.5 x 1.0 x It is apparent from the results shown in Table 2, the superconducting thin films prepared in the condition defined by the i 1- present invention exhibit much higher critical current density than the comparative examples.

From such a fact that we can not find any unevenness on the surfaces of the thin films of compound oxides obtained by the present invention when the surfaces are observed by SEM at 10,000 magnifications, while there exist grains of several microns on the surfaces of the thin films obtained by the comparative examples, we can estimate that the structure of the superconducting thin films of compound oxides obtained by the process according to the present invention is uniform and compacted Example 3 Superconducting thin films are prepared by RF magnetron sputtering technique. Targets used in the Examples are ceramics of S compound oxides of Ln-Ba-Cu-O which are prepared by usual sintering technique in which material powders whose atomic ratio of Ln Ba Cu is adjusted to 1 2.24 4.35 is sintered. "Ln" stands for lanthanide elements shown in Table 3. Each targets has a disk-shape having a II diameter of 100 mm. The sputtering is carried out under the identical operational conditions for all samples. The operational conditions are as following: Substrate: MgO (001} plane Substrate temperature: 700 °C Atmosphere gas pressure: 0.1 Torr Sputtering gas: 02(20 High-frequency power: 40 W (0.51 W/cm 2 -21- 0 Si 4 4 44 4 ft 1 0 I I I I I I 0 4144 Sputtering time: 6 hours Thickness of the thin film: 0.88 pm Deposition rate: 0.35 A/sec Annealing: 900 "C 3 hours (cooled at a cooling rate of 5 °C/min) The critical *emperature, the critical current density and the surface roughness observed on the resulting thin films are summarized in Table 3.

The results are also shown in Table 3.

Table 3 Ln Critical temp. Critical current density Surface roughness Tc Jc (A/cm 2 Rmax (tm) Compara- Ho 82.0 850 0.07 tive Tm 83.0 860 0.06 Lu 81.0 840 0.0 Present Ho 82.4 2.0 x 106 0.001 invention Er 87.3 3.0 x 106 0.002 Y 80.9 1.5 x 106 0.002 Dy 83.9 2.5 x 106 0.002 Gd 81.4 1.8 x 10 6 0.001 Eu 80.4 1.0 x 106 0.002 Sm 80.4 1.0 x 106 0.001 Yb 80.0 0.9 x 106 0.002 Nd 80.5 1.1 x 106 0.002 La 79.0 0.8 x 106 0.001 Tm 82.4 1.9 x 106 0.003 Lu 79.0 0.9 x 106 0.002 It is apparent from the results shown in Table 3, the superconducting thin films prepared in the condition defined by the -22i__ present invention exhibit much higher critical current density than the comparative examples.

In the case of the present invention, although voids of several microns are observed in a very small portion (about 1 of the whole surface) of surfaces of the thin films prepared by the process according to the present invention, we can not find unevenness on the majority surface of the thin films when the surfaces are observed by SEM at 10,000 magnifications. To the contrary, in the case of the thin films of compound oxide obtained by the comparative examples, we find innumerable grains of several microns on the surfaces.

Example 4 Si Superconducting thin films are prepared by RF magnetron sputtering technique. Targets used in the Examples are ceramics of S' compound oxides of Ln-Ba-Cu-O which are prepared by usual sintering technique in which matrial powders whose atomic ratio of Ln Ba Cu is adjusted to 1 2.24 4.35 is sintered. "Ln" stands for lanthanide elements shown in Table 4. Each targets has a disk-shape having a diameter of 100 mm. The sputtering is carried out under the identical operational conditions for all samples. The operational conditions are as following: Substrate: MgO (001 plane Substrate temperature: 700 °C Atmosphere gas: 02/(02+Ar) Atmosphere gas pressure: 0.1 Torr High-frequency power: 150 W (1.9 W/cm 2 -23-

IA_^

Sputtering time: 6 hours Thickness of the thin film: 0.88 pm (Depostion rate 0.35 A/sec) After the deposition complete, the resulting thin film deposited on I the substrate is heated in 02 of atmospheric pressure at 900 °C for one hour and then cooled to ambient temperature at a cooling rate of OC/min. The critical temperature and the critical current density observed on the resulting thin films are summarized in Table 4.

The results are also shown in Table 4.

24 i

J

-24- c~l r~------u-rrmuer Table 4 Critical temperature Tc (K) Critical current density Jc (A/cm 2 4$ 4 44 4 4O Comparative Ho 81.9 800 Tm 82.1 810 Lu 81.9 790 Present Ho 82.6 2.2 x 106 invention Er 87.0 2.8 x 106 Y 81.0 1.5 x 10 6 Dy 82.7 2.4 x 106 Gd 81.5 1.8 x 106 Eu 80.2 1.0 x 106 Sm 80.4 1.0 x 106 Yb 80.0 0.9 x 106 Nd 80.4 1.0 x 106 La 79.5 0.9 x 106 Tm 81.0 1.2 x 10 6 Lu 79.5 1.8 x 106 It is apparent from the results shown in Table 4, the superconducting thin films prepared in the condition defined by the present invention exhibit much higher critical current density than the comparative examples.

From such a fact that we can not find any unevenness on the surfaces of the thin films of compound oxides obtained by the present invention when the surfaces are observed by SEM at 10,000 magnifications, while there exist grains of several microns on the surfaces of the thin films obtained by the comparative examples, we can estimate that the structure of the superconducting thin films of compound oxides

:I:

ii .1 ii obtained by the process according to the present invention is uniformn and compacted Example Superconducting thin films are prepared by RF magnetron sputtering technique. Targets used in the Examples are ceramics of compound oxides of Ln-Ba-Cu-O which are prepared by usual sintering technique in which material powders whose atomic ratio of Ln Ba Cu is adjusted to 1 2.24 4.35 is sintered. "Ln" stands for lanthanide elements shown in Table 5. Each targets has a disk-shape having a o diameter of 100 mm. The sputtering is carried out under the identical operational conditions for all samples. The operational conditions are as following: Substrate: MgO [001] plane Substrate temperature: 690 °C High-frequency power: 100 W (1.27 V//cm 2 Sputtering time: 6 hours SThickness of the thin film: 0.88 \tm Deposition rate 0.35 A/sec Atmosphere gas pressure: 0.15 Torr Atmosphere gas: O2/Ar (20/80) After the deposition complete, the resulting thin film deposited on the substrate is heated in 02 of atmospheric pressure at 910 'C for three hours and then cooled to ambient temperature at a cooling rate of °C/min. The critical temperature and the critical current density observed on the resulting thin films are summarized in Table 5. u' -26- -1 00 a 0 21 4 4 00 0, As comparative examples, sputtering is carried out under the same conditions as above except that the atmosphere gas pressure is changed to 0.0008 Torr and 0.7 Torr and the high-frequency power is increased to 150 W (1.9 W/cm 2 The results are also shown in Table Table Ln Critical temperature Critical current density Tc Jc (A/cm 2 Comparative Ho 81.0 450 Tm 81.0 450 Lu 81.4 460 Comparative Ho 81.0 450 Tm 81.0 870 Lu 81.8 910 Present Ho 82.0 1.9 x 106 invention Er 87.0 2.8 x 106 Y 81.0 1.9 x 106 Dy 83.0 2.5 x 106 Gd 81.0 1.7 x 106 Eu 80.2 1.0 x 106 Sm 80.5 1.1 x 106 Yb 80.0 0.9 x 106 Nd 80.5 1.1 x 106 La 79.2 0.8 x 106 Tm 81.8 1.7 x 106 Lu 79.2 0.9 x 106 Note atmosphere gas pressure 0.0008 Torr high-frequency power 150 W (1.9 W//cm 2 Note atmosphere gas pressure 0.7 Torr high-frequency power 150 W (1.9 W//cm 2 -27- -14- It is apparent from the results shown in Table 5, the superconducting thin films prepared in the condition defined by the present invention exhibit much higher critical current density than the comparative examples.

We can not find unevenness on about 98 of the whole surfaces of the thin films of compound oxides obtained by the present invention when the surfaces are observed by SEM at 10,000 magnifications. To the contrary, there exist grains of several microns on the surfaces of the thin films obtained by the comparative examples.

io o Example 6 Superconducting wires are produced by RF magnetron sputtering technique.

A core used is a rod of MgO having a length of 150 mm and a diameter of 1 mm which is manufactured by molten drawing technique.

The rod is rotated about its own axis in front of a substrate holder in a chamber of a RF magnetron sputtering machine during the sputtering operation.

Targets used in the Examples are ceramics of compound oxides of 0 J Ln-Ba-Cu-O which are prepared by usual sintering technique in which material powders whose atomic ratio of Ln Ba Cu is adjusted to 1 S* 2.24 4.35 is sintered. "Ln" stands for lanthanide elements shown in Table 6. Each targets has a disk-shape having a diameter of 100 mm.

The sputtering is carried out under the identical operational conditions for all samples. The operational conditions are as following: Heating temperature of the core: 700 °C J i.

-28- 4

S,,

Sputtering pressure: 0.1 Torr Oxygen contents: 02(20 High-frequency power: 40 W (0.51 W/cm 2 Sputtering time: 6 hours Deposition rate: 0.30 A/sec Annealing: 900 oC/3 hours (cooled at a cooling rate of 5 oC/min) The critical temperature, the critical current density and the surface roughness observed on the resulting thin films are summarized in Table 6.

Table 6 o 4,44 4 4* 4, Sample No.

Ln Critical temp.

Tc (K) Critical current density Jc (A/cm 2 Surface roughness Rmax (p.m) I. I. I 82.0 88.1 81.0 84.0 77.1 78.1 79.2 75.1 72.3 78.2 2.0 x 106 2.0 x 106 2.0 x 106 1.8 x 106 0.1 x 106 0.5 x 106 0.6 x 106 0.3 x 106 0.1 x 106 0.5 x 106 0.008 0.009 0.010 0.022 0.012 0.008 0.032 0.031 0.042 0.012 I 4 In the case of the present invention, although voids of several microns are observed in a very small portion (about 1 of the whole surface) on surfaces of the thin films prepared, we can not find unevenness on the majority surface of the thin films when the surfaces are observed by SEM at 10,000 magnifications. To the contrary, in the case -29i of the thin films of compound oxide obtained by the comparative examples, we find innumerable grains of several microns on the surfaces.

(La -xa2Cu04 type superconductors Example 7 Superconducting thin films are prepared by RF magnetron sputtering technique.

Targets used in the Examples are sintered blocks of compound oxides whose atomic ratio of La Ba (or Sr) Cu is adjusted to 1.8 0.2 1. Each target has a disk-shape having a diameter of 100 mm. The S sputtering is carried out under the following operational conditions: t 0 O Substrate: MgO (001) plane Atmosphere gas: 02/(02+Ar) Atmosphere gas pressure: 0.1 Torr Substrate temperature: 700 °C High-frequency power: 40 W (0.51 W/cm 2 SSputtering time: 6 hours Thickness of the thin film: 0.88 utm (Deposition rate 0.35 A/sec) After the deposition complete, the resulting thin film deposited on the substrate is heated in air at 900 °C for three hours and then cooled to ambient temperature at a cooling rate of 5 oC/min.

As comparative examples, sputtering is carried out under the same conditions as above except that the high-frequency power is increased to 150 W (1.9 W/cm 2 The results are also shown in Table 7.

Table 7 oc Critical temperature Critical current density Tc Jc (A/cm 2 Comparative Ba 28 500 Sr 38 1,000 Present Ba 28 1 x 105 invention Sr 38 1 x 106 S Example 8 Superconducting thin films are prepared by RF magnetron Sro sputtering technique.

Targets used in the Examples are sintered blocks of compound oxides whose atomic ratios of La Ba (or Sr) Cu are adjusted to 1.8 0.2 1. Each target has a disk-shape having a diameter of 100 mm. The sputtering is carried out under the following operational conditions: Substrate: MgO {001} plane Atmosphere gas: 02/(02+Ar) Atmosphere gas pressure: 0.1 Torr Substrate temperature: 700 °C S' High-frequency power: 40 W (0.51 W/cm 2 ,2 Sputtering time: 6 hours Thickness of the thin film: 0.88 tm (Deposition rate 0.35 A/sec) -31 After the deposition complete, the resulting thin film deposited on the substrate is heated in air at 900 °C for one hour and then cooled to ambient temperature at a cooling rate of 5 °C/min.

As comparative examples, sputtering is carried out under the same conditions as above except that the deposition rate is increased to A/sec.

The results are also shown in Table 8.

Table 8 *0I

P)

4.

4 4 44 a Critical temperature Critical current density Tc Jc (A/cm 2 Comparative Ba 28 Sr 38 150 Present Ba 28 1 x 105 invention Sr 38 1 x 106 Example 9 Superconducting thin films are prepared by RF magnetron sputtering technique.

Targets used in the Examples are sintered blocks of compound oxides of an element a (Ba or Sr), La and Cu which are prepared by usual sintering technique in which material powders whose atomic ratio of La a Cu is adjusted to 1.8 0.2 1 is sintered. Each target has a diskshape having a diameter of 100 mm. The sputtering is carried out under the identical operational conditions for all samples. The operational conditions are as following: -32- Substrate: MgO {001} plane Substrate temperature: 700 °C Atmosphere gas pressure: 0.1 Torr Sputtering gas: 02 (20 Ar (80 High-frequency power: 40 W (0.51 W/cm 2 Sputtering time: 6 hours Thickness of the thin film: 0.88 jim Deposition rate 0.35 A/sec Annealing 900 oC 3 hours (Cooled at a cooling rate of 5 °C min) SAs comparative examples, sputtering is carried out under the same conditions as above except that the deposition rate is increased to A/sec.

The results are also shown in Table 9.

Table 9 a Critical temp. Critical current density Surface roughness Tc Jc (A/cm 2 Rmax (4m) Compara- Ba 28 500 tive Sr 38 1,000 0.3 Present Ba 28 2.0 x 106 0.05 invention Sr 38 3.0 x 106 0.03 It is apparent from the results shown in Table 9, the superconducting thin films prepared in the condition defined by the -33- 1- P .1 1:k 1' present invention exhibit much higher critical current density than the comparative examples.

Although voids of several microns are observed at a very small portion (about 1 of the whole surface) of surfaces of the thin films prepared by the present invention, we can not find unevenness on the majority surface of the thin films when the surfaces are observed by SEM at 10,000 magnifications. To the contrary, in the case of the thin filmns of compound oxide obtained by the comparative examples, we find innumerable grains of several microns on the surfaces.

To Example Superconducting thin films are prepared by RF magnetron 4 sputtering technique. Targets used in the Examples are sintered blocks of compound oxides whose atomic ratios of La Ba (or Sr) Cu are adjusted to 1.8 P 1. Each target has a disk-shape having a diameter of 100 mm. The sputtering is carried out under the following operational conditions: Substrate: MgO (001) plane Atmosphere gas: 02/(02+Ar) Substrate temperature: 700 0

C

Atmosphere gas pressure: 0.1 Torr High-frequency power: 150 W (1.9 W/cm 2 Sputtering time: 6 hours Thickness of the thin film: 0.88 gm (Deposition rate 0.35 A/sec) i -34- After the deposition complete, the resulting thin film deposited on the substrate is heated in air at 900 °C for one hour and then cooled to ambient temperature at a cooling rate of 5 °C/min.

The results are also shown in Table Table -1 00 Jo r o oo a oo 01 o 0 0 0 0 0 0 oo a 0 0o20 a (1>3 6 i a Critical temperature Critical current density Tc Jc (A/cm 2 Comparative Ba 28 500 Sr 38 1,000 Present Ba 28 1 x 105 invention Sr 38 1x 106 From such a fact that we can not find any unevenness on the surfaces of the thin films of compound oxides obtained by the present invention when the surfaces are observed by SEM at 10,000 magnifications, while there exist grains of several microns on the surfaces of the thin films obtained by the comparative examples, we can estimate that the structure of the superconducting thin films of compound oxides obtained by the process according to the present invention is uniform and compacted ]1 Example 1. 1 Superconducting thin films are prepared by RF magnetron sputtering technique.

Targets used in the Examples are sintered blocks of compound oxides of an element o (Ba or Sr), La and Cu which are prepared by usual sintering technique in which material powders whose atomic ratio of La a Cu is adjusted to 1.8 0.2 1 is sintered. Each target has a diskshape having a diameter of 100 mm. The sputtering is carried out under the identical operational conditions for all samples. The operational conditions are as following: Substrate: MgO (001) plane Substrate temperature: 690 °C High-frequency power: 100 W (1.27 W/cm 2 Sputtering time: 6 hours Thickness of the thin film: 0.88 jLm Deposition rate 0.35 A/sec Atmosphere gas pressure: 0.15 Torr Atmosphere gas: 02/Ar After the deposition complete, the resulting thin film deposited on the substrate is heated in air at 910 'C for three hours and then cooled to ambient temperature at a cooling rate of 5 °C/min. The results are also shown in Table 11.

As comparative examples, sputtering is carried out under the same conditions as above except that the atmosphere gas pressure is changed to 0.0008 Torr and 0.7 Torr. The results are also shown in Table 11.

-36i

I

~pj Table 11 a 4 o a Critical temperature Critical current density Tc Jc (A/cm 2 Comparative Ba 5 Sr 10 200 Comparative Ba 6 Sr 8 180 Present Ba 28 1 x 105 invention Sr 38 1 x 106 Note: atmosphere gas pressure 0.0008 Torr atmosphere gas pressure 0.7 Torr We can not find unevenness on about 98 of the whole surfaces of the thin films of compound oxides obtained by the present invention when the surfaces are observed by SEM at 10,000 magnifications. To the contrary, there exist grains of several microns on the surfaces of the thin films obtained by the comparative examples.

Ln1Ba2Cu3Q7-8 type superconducting thin films Example 12 Superconducting thin films are prepared by RF sputtering technique. Targets used in the Examples are compound oxides of Ln-Ba- Cu-O ceramics each having an atomic ratio of Ln Ba Cu 1 2.24 4.35. "Ln" stands for lanthanide elements shown in Table 12. Each target has a disk-shape having a diameter of 100 mm. The sputtering is carried -37- 1 out under an identical operational condition for all samples. The operational conditions are as following: Substrate: MgO (001) plane Substrate temperature: 700 °C Atmosphere gas pressure: 0.01 to 0.1 Torr High-frequency power: 40 W (0.51 W/cm 2 Sputtering time: 6 hours Thickness of the thin film: 0.8 nLm After the deposition complete, the resulting thin film deposited on the substrate is heated at 900 oC for one hour and then cooled to ambient temperature at a cooling rate of 5 "C/min.

As comparative examples, a superconducting thin film of compound oxide containing Ho is prepared under the same conditions as above except that the high-frequency power is increase to 150 W (1.9 W/cm 2 The results are also shown in Table 12.

-38- 3 Fl Table 12 2f.

*4 Ln Critical temperature Critical current density Tc Jc (A/cm 2 Comparative Ho 82.0 850 Present Ho 82.1 2.1 x 106 invention Er 88.2 2.0 x 106 Y 81.6 2.2 x 106 Dy 84.5 1.9 x 106 Gd '17.8 0.1 x 106 Eu 78.4 0.7 x 106 Sm 80.1 0.9 x 106 Yb 77.2 0.6 x 106 Nd 77.5 0.3 x 106 La 78.3 0.4 x 106 It is apparent from the results shown in Table 1, the superconducting thin films prepared in the condition defined by the present invention exhibit much higher critical current density than the comparative examples.

From such a fact that we can not find any unevenness on the surfaces of the thin films of compounA, oxides obtained by the present invention when the surfaces a. oserved by SEM at 10,000 magnifications, while there exist grains of several microns on the surfaces of the thin films obtained by the comparative examples, we canu- estimate that the structure of the superconducting thin films of compound oxides obtained by the process according to the present invention is uniform and compacted -39-

Claims

1. A superconducting composite consisting of a substrate and a superconducting thin film which is deposited on said substrate and which comprises superconducting compound oxide whose critical temperature is higher than 28K, wherein a substantial portion of the surfaced of said superconducting thin film has a smooth surface having a surface roughness of Rmax (datum length=1,000m) of less than 0.2pm.

2. The superconducting composite set forth in Claim 1, characterized in that said superconducting thin film is 0 formula: SLn Ba2Cu 307 in which Ln stands for at least one lanthanide element selected from a group comprising La, Nd, Sm, Eu, Gd, Dy, Ho, Y, Er, Yb, Tm and Lu and 6 is a number which satisfies a range 0 (6 1i,.

3. The superconducting composite set forth in Claim 1, characterized in that said superconducting thin film is composed of a compound oxide represented by the general formula: (Lal-x 2 CuO 4 in which a stands for Ba or Sr and is a number satisfying a range of 0 x 1.

4. The superconducting composite set forth in any one of Claims 1 to 3, characterized in that said substrate is made of a single crystal of oxide whose lattice distance is nearly same as the lattice distance of the crystal of said compound oxide. The superconducting composite set forth in Claim 4, i characterized in that said substrate is made of a single p crystal of MgO, SrTiO 3 or ZrO.

41- 6. The superconducting composite set forth in Claim characterized in that said superconducting thin film is deposited on a [001] plane or [110] plane of a substrate made of a single crystal of MgO or SrTiO 3 7. A process for producing a superconductor including a physical vapour deposition stage for depositing a superconducting thin film comprises superconducting compound oxide whose critical temperature is higher than 28K on a substrate, characterized in that the physical vapour deposition is carried out in such a manner that a substantial portion of the surface of said superconducting thin film obtained finally has a smooth surface having a surface roughness of Rmax (datum length 1,000 pm) of less than 0.2 pm by controlling operational conditions during the physical vapour deposition. 8. The process set forth in Claim 7, characterized in that said superconducting thin film is composed of a compound oxide represented by the general formula: LnlBa2Cu307-6 in which Ln stands for at least one lanthanide element selected from a group comprising La, Nd, Sm, Eu, Gd, Dy, Ho, Y, Er, Yb, Tm and Lu and 6 is a number which satisfies a range 0 1i. 9. The process set forth in Claim 7, characterized in that said superconducting thin film is composed of a compound oxide represented by the general formula: (La X) 2 Cu0 4 I1 in which a stands for Ba or Sr and is a number satisfying a range of 0 x 1. The process set forth in any one of Claims 7 to 9, characterized in that said substrate is made of a single crystal of oxide whose lattice distance is nearly same as the lattice distance of the crystal of said compound oxide. Ar. Oq U1 i 0ti i r 42 11. The process set forth in Claim 10, characterized in that said substrate is made of a single crystal of MgO, SrTiO 3 or ZrO 2 12. The process set forth in Claim 11, characterized in that said superconducting thin film is deposited on a [001] plane or [110] plane of a substrate made of a single crystal of MgO or SrTiO 3 13. The process set forth in any one of Claims 7 to 12, characterized in that said deposition rate in the physical vapour disposition stage is within a range of 0.05 to 1 A/sec. 14. The process set forth in any one of Claims 7 to 13, C characterized in that the atmosphere gas in the physical vapour deposition stage is a mixed gas consiLting of inert gas and oxygen, the prop.rtion of oxygen in said mixed gas being within a range of 5 to The process set forth in Claim 14, characterized in that said proportion of oxygen in said mixed gas is within a range of 10 to 16. The process set forth in any one of Claims 7 to characterized in that said substrate is heated during the physical vapour deposition stage. 17. The process set forth in Claim 16, characterized in that said substrate is heated to a temperature ranging from 200 to 950°C. 18. The process set forth in Claim 17, characterized in that said substrate is heated to a temperature ranging from 500 to 920°C. 19. The process set forth in any one of Claims 7 to 18, characterized in that said physical vapour deposition is performed by sputtering technique which is carried out under a sputtering gas pressure ranging from 0.001 to i Torr. ii 43 The process set forth in Claim 19, characterized in that said sputtering gas pressure is within a range of 0.01 to 0.3 Torr. 21. The process set forth in Claims 19 or characterized in that the oxygen contents during the sputtering stage is within a range of 5 to 95% by molecular. 22. The process set forth in any one of Claims 19 to 21, characterized in that said physical vapour deposition is performed by RF sputtering technique which is carried out at a high-frequency power ranging from 0.064 to o' 2.55 W/cm2 04 23. The process set forth in Claim 22, characterized in that said high-frequency power is within a range of from 0.064 to 1.27 W/cm 2 24. The process set forth in any one of Claims 19 to 23, characterized in that said sputtering is magnetron sputtering. The process set forth in any one of Claims 7 to 24, characterized in that, after deposition of the thin film complete, the resulting thin film is further heat-treated in an oxygen-containing atmosphere. 26. The process set forth in Claim 25, characterized in that the heat-treatment is performed at a temperature ranging 800 to 960°C. 27. The process set forth in Claim 26, characterized in that, after the thin film is heated, the thin film is then cooled slowly at a cooling rate of less than 10 0 C/min. 28. The process set forth in any one of Claims 25 to 27, characterized in that said heat-treatment is carried out at a partial oxygen pressure ranging 0.1 to 10 atm. 29. A superconducting wire comprising a core and a superconducting thin film which comprises superconducting compound oxide whose critical temperature is higher than 28K and which ir. deposited on a surface of said core by L i. -31- i; S44 physical vapour deposition technique, wherein a substantial portion of the surface of said superconducting thin film has a smooth surface having a surface roughness of Rmax (datum length 1,000 pm) of less than 0.2 ym. The superconducting wire set forth in Claim 29, characterized in that said superconducting thin film is composed of a compound oxide represented by the general formula: LnlBa2Cu307_ 6 L n1 a2 C u3 07-6 in which Ln stands for at least one lanthanide element selected from a group comprising La, Nd, Sm, Eu, Gd, Dy, Ho, Y, Er, Yb, Tm and Lu and 6 is a number which satisfies a range 0 1. 31. The superconducting wire set forth in Claim 29, characterized in that said superconducting thin film is composed of a compound oxide represented by the general formula: (Lal 1 -xx) 2 Cu O 4 in which a stands for Ba or Sr and is a number satisfying a range of 0 x 1. 32. The superconducting wire set forth in any one of Claim 29 to 31, characterized in that said core is made of metal. 33. The superconducting wire set forth in Claim 32, characterized in that said superconducting thin film is deposited on a thin film layer made of ceramic which is deposited on said core. 34. The superconducting wire set forth in Claim 33, characterized in that said ceramic is an oxide. The superconducting wire set forth in Claims 33 or 34, characterized in that said ceramic is of a single crystal, polycrystal or glass. iS 8 r I 45 o p 0 0 o o V o 0 04 00 o D Vl 0a 0 04 36. The superconducting wire set forth in Claim characterized in that said single crystal or polycrystal contains an oxide crystal whose lattice distance is nearly same as the lattice distance of the crystal of said compound oxide. 37. The superconducting wire set forth in any one of Claims 33 to 36, characterized in that said ceramic is made of a single crystal of MgO, SrTiO 3 or ZrO 2 38. The superconducting wire set forth in any one of Claims 33 to 37, characterized in that surface of said ceramic has a [001] plane or [110] plane. 39. The superconducting wire set forth in any one of Claims 29 to 31, characterized in that said core is made of ceramic. 40. The superconducting wire set forth in Claim 39, characterized in that said ceramic is an oxide. 41. The superconducting wire set forth in Claims 39 or characterized in that said ceramic is of a single crystal, polycrystal or glass.

42. The superconducting wire set forth in Claim 41, characterized in that said single crystal or polycrystal contains an oxide crystal whose lattice distance is nearly same as the lattice distance of the crystal of said compound oxide.

43. The superconducting wire set forth in any one of Claims 39 to 42, characterized in that said ceramic is made of a single crystal of MgO, SrTiO 3 or ZrO 2

44. The superconducting wire set forth in any one of Claims 39 to 43, characterized in that a surface of said ceramic has a [001] plane or [110] plane. A process for producing a superconducting wire comprising a core and a superconducting thin film which comprise.. superconducting compound oxide whose critical temperature is higher than 28K and which is deposited on a surface of said core by physical vapour deposition l/ 46 technique, wherein the physical vapour deposition is carried out in such a manner that a substantial portion of the surface of said superconducting thin film obtained finally has a smooth surface having a surface roughness of Rmax (datum length 1,000 Mm) of less than 0.2 pm by controlling operational conditions during the physical vapour deposition.

46. The process set forth in Claim 45, characterized in that said superconducting thin film is composed of a compound oxide represented by the general formula: Ln Ba2Cu 07_ 6 1 2 3 in which Ln stands for at least one lanthanide element selected from a group comprising La, Nd, Sm, Eu, Gd, Dy, Ho, Y, Er, Yb, Tm and Lu and 6 is a number which satisfies a range O 1i.

47. The process set forth in Claim 45, characterized in that said superconducting thin film is composed of a compound oxide represented by the general formula: (La 1 xa~) 2 CuO 4 in which a stands for Ba or Sr and is a number satisfying a range of 0 x 1.

48. The process set forth in any one of Claims 45 to 47, characterized in that said core is made of metal.

49. The process set forth in Claim 48, characterized in that superconducting thin filnr is deposited on a thin film layer made of ceramic which is deposited on said core. The process set forth in Claim 49, characterized in that said ceramic is a oxide.

51. The process set forth in Claims 49 or characterized in that said ceramic is of a single crystal, polycrystal or glass. LUi a. u Uj ,.d 9 ;j i r i 47

52. The process set forth in Claim 51, characterized in that said single crystal or polycrystal contains an oxide crystal whose lattice distance is nearly same as the lattice distance of the crystal of said compound oxide. 5 53. The process set forth in any one of Claims 49 to 52, characterized in that said ceramic is made of a single crystal of MgO, SrTiO 3 or ZrO 2

54. The process set forth in any one of Claims 49 to 53, characterized in that a surface of said ceramic has a [001] plane or [110] plane. The process set forth in any one of Claims 45 to 47, characterized in that said core is made of ceramic.

56. The process set forth in Claim 55, characterized in that said ceramic is an oxide.

57. The process set forth in Claims 55 or 56, characterized in that said ceramic is of a single crystal, polycrystal or glass.

58. The process set forth in Claim 57, characterized in that said single crystal or polycrystal contains an oxide crystal whose lattice distance is nearly same as the lattice distance of the crystal of said compound oxide.

59. The process set forth in any one of Claims 55 to 58, characterized in that said ceramic is made of a single crystal of MgO, SrTiO 3 or ZrO 2

60. The process set forth in any one of Claims 55 to 59, characterized in that a surface of said ceramic has a [001] plane or [110] plane.

61. The process set forth in any one of Claims 45 to characterized in that said deposition rate in the physical vapour deposition stage is within a range of 0.05 to 1 &/sec. ~14 0 txrL~1 a L 48

62. The process set forth in any one of Claims 45 to 61, characterized in that atmosphere gas used in the physical vapour depositioi "tage is a mixed gas consisting of inert gas and oxygen, the proportion of oxygen in said mixed gas being within a range of 5 to j 63. The process set forth in Claim 62, characterized in Sthat said proportion of oxygen in said mixed gas is within a range of 10 to

64. The process set forth in any one of Claims 45 to 63, characterized in that said substrate is heated during the physical vapour deposition stage.

65. The process set forth in Claim 64, characterized in that said substrate is heated to a temperature ranging e from 200 to 950°C.

66. The process set forth in Claim 65, characterized in I that said substrate is heated to a temperature ranging from 500 to 9200C.

67. The process set forth in any one of Claims 45 to 66, characterized in that said physical vapour deposition is performed by sputtering technique which is carried out under a sputtering gas pressure ranging from 0.001 to 1 0.5 Torr.

68. The process set forth in Claim 67, characterized in o that said sputtering gas pressure is within a range of 0.01 to 0.3 Torr.

69. The process set forth in Claims 67 or 68, characterized in that the oxygen contents during the sputtering stage is within a range of 5 to 95% by molecular. The process set forth in any one of Claims 67 to 69, characterized in that said physical vapour deposition is performed by RF sputtering technique which is carried out at a high-frequency power ranging from 0.064 to 2.55 W/cm 2 V T0 T0 J i 49

71. The process set forth in Claim 70, characterized in that said high-frequency power is within a range of from 2 0.064 to 1.27 W/cm

72. The process set forth in any one of Claims 67 to 71, characterized in that said sputtering is magnetron sputtering.

73. The process set forth in any one of Claims 45 to 72, characterized in that, after deposition of the thin film complete, the resulting thin film is further heat-treated in an oxygen-containing atmosphere.

74. The process set forth in Claim 73, characterized in that said heat-treatment is performed at a temperature ranging 800 to 960°C. The process set forth in Claim 74, characterized in SQ.that, after the thin film is heated, the thin film is then cooled slowly at a cooling rate of less than 10 0 C/min.

76. The process set forth in any one of Claims 73 to characterized in that said heat-treatment is carried out at a partial oxygen pressure ranging 0.1i to 10 atm.

77. A superconducting composite substantially as hereinbefore described with reference to the accompanying m examples but excluding comparative examples.

78. A process for producing a superconductor o substantially as hereinbefore described with reference to the accompanying examples but excluding comparative examples. DATED this 27 day of February 1991 SUMITOIOO ELECTRIC INDUSTRIES LTD Patent Attorneys for the Applicant: F.B. RICE CO. NT o