KR20250010892A - Mg-doped La0.7Sr0.3-xMgxMnO3 ceramics and its manufacturing method - Google Patents

Abstract

The present invention relates to Mg-doped La _0.7 Sr _0.3-x Mg _x MnO ₃ ceramics characterized by replacing Sr ²⁺ with Mg ²⁺ having a different ionic radius in La _0.7 Sr _0.3 MnO ₃ (LSMO) exhibiting excellent electrical conductivity characteristics, and a method for producing the same. By adding MgO to La _0.7 Sr _0.3 MnO ₃ (LSMO), it is possible to produce the ceramics in a short period of time compared to a conventional solid-state reaction method, thereby exhibiting high productivity. In addition, it is expected that the ceramics can be utilized as a thermistor material for temperature sensors since it exhibits a NTCR (negative temperature coefficient of resistance) characteristic in which the electrical resistance linearly decreases with temperature change at room temperature.

Description

{Mg-doped La0.7Sr0.3-xMgxMnO3 ceramics and its manufacturing method}

The present invention relates to Mg-doped La _0.7 Sr _0.3-x Mg _{x MnO 3} ceramics and a method for producing the same, and more specifically, to ceramics characterized by having a NTCR (negative temperature coefficient of resistance) characteristic in which the electrical resistance linearly decreases with temperature change near room temperature by substituting Sr ²⁺ with Mg ²⁺ having a different ionic _radius in La _0.7 Sr 0.3 MnO 3 (LSMO) exhibiting excellent electrical conductivity characteristics, and a method for producing the same.

Manganese compounds with a perovskite structure, R _1-x A _x MnO ₃ (R = rare-earth, A = alkaline-earth element), show changes in magnetic state depending on the constituent elements and manufacturing method, and metal-nonmetal transition characteristics depending on the applied temperature and magnetic field.

In particular, as known from non-patent documents 1 and 2, active research is being conducted for applications to magnetic field sensors, magnetic random access memory (MRAM), spintronic devices, etc. by utilizing the colossal magnetoresistance characteristics according to the application of an external magnetic field, and various patents such as patent documents 1 and 2 are being applied for.

LaMnO ₃ has Mn ³⁺ at the center of the MnO ₆ oxygen octahedral structure, which has five 3d orbitals separated by three t ² _g and two e _g orbitals, and has an electron configuration of 3d ⁴ (t ³ _2g , e ¹ _g ). When Sr ²⁺ ions are substituted for La ³⁺ ions, some of the Mn ions are converted from Mn ³⁺ to Mn ⁴⁺ to maintain electrical neutrality, and at this time, the electron configuration of the Mn ⁴⁺ ion becomes 3d ³ (t ³ _2g , e ⁰ _g ). Therefore, hole doping is induced by substituting Sr ²⁺ ions for La ³⁺ ions. When Mn ³⁺ and Mn ⁴⁺ ions are mixed, high magnetoresistance characteristics are exhibited due to double exchange (DE) interaction mediated by adjacent oxygen ions in the Mn ³⁺ -O-Mn ⁴⁺ arrangement.

In general, studies on R _1-x A _x MnO ₃ have mainly focused on hole doping and Mn ⁴⁺ generation by substitution of A ²⁺ elements and compositional changes for various R ³⁺ elements, and examination of electromagnetic properties by DE interaction. However, studies on structural changes such as grains, grain boundaries, pores, and lattice distortion are insufficient.

In the present invention, a La _0.7 Sr _0.3 MnO ₃ (LSMO) material exhibiting excellent electrical conductivity was selected, and then the structural and electrical characteristics were observed by substituting Sr ²⁺ with Mg ²⁺ having a different ionic radius, thereby manufacturing a ceramic that can be used as a thermistor for a temperature sensor.

Republic of Korea Patent Publication No. 10-1647354 (August 4, 2016) Republic of Korea Patent Publication No. 10-1381643 (2014.03.31)

K. Das, P. Dasgupta, A. Poddar, and I. Das, Sci. Rep., 6, 20351 (2016). [DOI: https://doi.org/10.1038/srep20351] J. Heremans, J. Phys. D: Appl. Phys., 26, 1149 (1993). [DOI: https://doi.org/10.1088/0022-3727/26/8/001]

The present invention was devised to manufacture a thermistor ceramic that can be used as a temperature sensor by selecting a La _0.7 Sr _0.3 MnO ₃ (LSMO) material exhibiting excellent electrical conductivity properties and observing the structural and electrical properties according to substitution of Sr ²⁺ with Mg ²⁺ having a different ionic radius, and the purpose of the present invention is to provide Mg-doped La _0.7 Sr _0.3-x Mg _x MnO ₃ ceramics and a manufacturing method therefor.

The technical problems to be achieved by the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned can be clearly understood by a person having ordinary skill in the art from the description of the present invention.

In order to achieve the above object, a preferred embodiment of the present invention is a method for manufacturing Mg-doped La _0.7 Sr _{0.3 -} x Mg x MnO 3 ceramics, characterized by including the steps of (S1) mixing raw materials of La ₂ O ₃ , SrCO 3 , MgO, and Mn 2 O 3 ; the step of (S2) adding a dispersion medium to the mixed raw materials and pulverizing the mixture ; the step of (S3) calcining the pulverized mixture for a solid-state reaction ; the step of ( _S4 ) mixing a binder into the _calcined mixture powder and sintering it ; and the step of _{( S5} ) cooling the sintered mixture.

In the above raw material mixing step (S1), the raw materials La ₂ O ₃ , SrCO ₃ , MgO, and Mn ₂ O ₃ are stoichiometrically weighed and mixed according to the composition formula of La _0.7 Sr _0.3-x Mg _x MnO ₃ , and it is characterized in that in La _0.7 Sr _0.3-x Mg _x MnO ₃ , x is 0.05 ≤ x ≤ 0.2.

In the above mixture grinding step (S2), 30 to 50 parts by weight of a dispersion medium are mixed with 100 parts by weight of the mixture, and then the mixture is ground for 22 to 26 hours using a zirconia ball mill. The dispersion medium is characterized in that it is one or more mixed solvents selected from methanol, ethanol, isopropyl alcohol, acetone, and distilled water.

In the above calcination step (S3), the pulverized mixture is characterized by being calcined at 840°C to 860°C for 110 to 130 minutes.

In the above sintering step (S4), 3 to 5 parts by weight of a binder are added to 100 parts by weight of the calcined mixture powder, and the mixed mixture is sintered at 1,200°C to 1,400°C for 150 to 210 minutes, and the binder is characterized in that it is a mixture of one or more selected from PVA (polyvinylalcohol), PEG (polyethyleneglycol), methyl cellulose, and ethyl cellulose.

In the above cooling step (S5), the sintered mixture is characterized by cooling to room temperature.

The La _0.7 Sr _0.3-x Mg _x MnO ₃ (0.05 ≤ x ≤ 0.2) ceramics manufactured by the above method are characterized by having a room temperature resistivity of 35 Ω-cm to 50 Ω-cm and a B _25/65 constant of 380 K to 400 K.

Meanwhile, a preferred embodiment of the present invention provides another solution to the problem, which is a Mg-doped La _0.7 Sr _0.3-x Mg _x MnO ₃ ceramic characterized in that La _0.7 Sr _0.3-x Mg _x MnO ₃ (0.05 ≤ x ≤ 0.2) is manufactured by the above method.

The La _0.7 Sr _0.3-x Mg _x MnO ₃ (0.05 ≤ x ≤ 0.2) ceramics according to the present invention can be manufactured in a short period of time compared to the conventional solid-state reaction method, thereby having the effect of high productivity.

In addition, the La _0.7 Sr _0.3-x Mg _x MnO ₃ (0.05 ≤ x ≤ 0.2) ceramics according to the present invention exhibit NCTR characteristics in which the electrical resistance of La _0.7 Sr _0.3-x Mg _x MnO ₃ linearly decreases at room temperature by selecting a La _0.7 Sr _0.3 MnO ₃ (LSMO) material exhibiting excellent electrical conductivity characteristics and then replacing Sr ²⁺ with Mg ²⁺ having a different ionic radius, so that it can be utilized as a thermistor material for a temperature sensor.

The effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description of the claims.

Figure 1 is a diagram showing a preferred embodiment of the present invention of Mg-doped La _0.7 Sr _0.3-x Mg _x MnO ₃ (0.05 ≤ x ≤ 0.2). This is a process block diagram explaining the manufacturing process of ceramics.
Figure 2 is a diagram showing a preferred embodiment of La _0.7 Sr _0.3-x Mg _x MnO ₃ (0.05 ≤ x ≤ 0.2) according to the present invention. This shows the X-ray diffraction pattern according to the amount of Mg ²⁺ added to the ceramics.
Figure 3 is a La _0.7 Sr _0.3-x Mg _x MnO ₃ (0.05 ≤ x ≤ 0.2) manufactured according to a preferred embodiment of the present invention. The surface microstructure of ceramics according to the amount of Mg ²⁺ added is shown in SEM photographs (magnification x 20,000).
Figure 4 is a diagram showing La _0.7 Sr _0.3-x Mg _x MnO ₃ (0.05 ≤ x ≤ 0.2) manufactured according to a preferred embodiment of the present invention. This shows the room temperature resistivity according to the amount of Mg ²⁺ added to the ceramics.
FIG. 5 is a diagram showing a La _0.7 Sr _0.3-x Mg _x MnO ₃ (0.05 ≤ x ≤ 0.2) manufactured according to a preferred embodiment of the present invention. This shows the electrical resistance of ceramics according to the amount of Mg ²⁺ added and temperature.
Figure 6 is a graph of La _0.7 Sr _0.3-x Mg _x MnO ₃ (0.05 ≤ x ≤ 0.2) manufactured according to a preferred embodiment of the present invention. This shows the B _25/65 -integer according to the amount of Mg ²⁺ added to ceramics.
Figure 7 is a graph of La _0.7 Sr _0.3-x Mg _x MnO ₃ (0.05 ≤ x ≤ 0.2) manufactured according to a preferred embodiment of the present invention. This shows the ln (R·T ^-1 ) vs 1/T ^1/4 curve according to the amount of Mg ²⁺ added to ceramics.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings.

The terms used in this specification are selected from the most widely used general terms possible while considering the functions of the present invention, but they may vary depending on the intention of engineers working in the field, precedents, the emergence of new technologies, etc. In addition, in certain cases, there are terms arbitrarily selected by the applicant, and in this case, the meanings thereof will be described in detail in the description of the relevant invention. Therefore, the terms used in the present invention should be defined based on the meanings of the terms and the overall contents of the present invention, rather than simply the names of the terms.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms defined in commonly used dictionaries, such as those defined in common usage, should be interpreted as having a meaning consistent with the meaning they have in the context of the relevant art, and will not be interpreted in an idealized or overly formal sense unless expressly defined in this application.

When a part of a specification is said to "include" a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise stated.

The numerical ranges are inclusive of the numbers defined in the above ranges. Every maximum numerical limitation given throughout this specification will include every lower numerical limitation, as if that lower numerical limitation were expressly written out. Every minimum numerical limitation given throughout this specification will include every higher numerical limitation, as if that higher numerical limitation were expressly written out. Every numerical limitation given throughout this specification will include every better numerical range within that broader numerical range, as if that narrower numerical limitation were expressly written out.

Hereinafter, examples of the present invention will be described in detail, but it is obvious that the present invention is not limited to the following examples.

A preferred embodiment of the present invention comprises a step (S1) of mixing raw materials of La ₂ O ₃ , SrCO ₃ , MgO, and Mn ₂ O ₃ ; a step (S2) of adding a dispersion medium to the mixed raw materials and pulverizing the mixture ; a step (S3) of calcining the pulverized mixture for a solid-state reaction ; a step (S4) of mixing a binder into the calcined mixture powder and sintering it ; and a step (S5) of cooling the sintered mixture.

For reference, in order to ensure a natural flow of context in the description of the specification of the present invention, it should be noted that 'Mg-doped La _0.7 Sr _0.3-x Mg _x MnO ₃ ' is written as 'LSMMO' and 'La _0.7 Sr _0.3 MnO ₃ ' is written as 'LSMO', either singly or in combination.

Hereinafter, Mg-doped La _0.7 Sr _0.3-x Mg _x MnO ₃ (0.05 ≤ x ≤ 0.2) according to a preferred embodiment of the present invention The manufacturing method of ceramics is explained in detail step by step as follows.

The above raw material mixing step (S1) is a step in which the raw materials La ₂ O ₃ , SrCO ₃ , MgO, and Mn ₂ O ₃ are stoichiometrically weighed and mixed according to the composition formula of La _0.7 Sr _0.3-x Mg _x MnO ₃ . In the above La _0.7 Sr _0.3-x Mg _x MnO ₃ , x is preferably 0.05 ≤ x ≤ 0.2.

In the above La _0.7 Sr _0.3-x Mg _x MnO ₃ , when x exceeds 0.2, as the amount of Mg ²⁺ added increases, the distortion of the unit cell, the concentration of oxygen attackers, and lattice defects mutually affect the electrical properties of the specimen, so there is a concern that the formation characteristics of the electrical resistance for temperature changes near room temperature may deteriorate.

In the above mixture grinding step (S2), it is preferable to mix 30 to 50 parts by weight of a dispersion medium with respect to 100 parts by weight of the mixture and then grind the mixture using a zirconia ball mill for 22 to 26 hours, but it is more preferable to mix 30 to 50 parts by weight of a dispersion medium with respect to 100 parts by weight of the mixture and then grind the mixture using a zirconia ball mill for 24 hours.

In addition, it is preferable that the dispersion medium of the mixture grinding step (S2) is one or more mixed solvents selected from methanol, ethanol, isopropyl alcohol, acetone, and distilled water, but it is more preferable to select ethanol as the dispersion medium.

If the amount of the dispersion medium mixed is less than the above-mentioned limited range, there is a concern that the mixture powder may not be sufficiently pulverized because the amount of the dispersion medium is relatively small compared to the amount of the mixture powder, and if it exceeds the above-mentioned limited range, there is a concern that the pulverization efficiency may be reduced because an excessive amount of dispersion medium is mixed in more than necessary.

The above calcination step (S3) is a step for causing a solid-state reaction of the above-mentioned pulverized mixture, and it is preferable to calcinate at 840°C to 860°C for 110 to 130 minutes, but it is more preferable to calcinate at 850°C for 120 minutes.

If the above calcination conditions are below the above-mentioned limited range, the mixed raw materials do not react sufficiently, resulting in La _0.7 Sr _0.3-x Mg _x MnO ₃ (0.05 ≤ x ≤ 0.2). There is a concern that the production efficiency of ceramics may decrease, and if the above-mentioned limited range is exceeded, there is a concern that an inefficient process may be performed due to excessive heat being applied.

In the above sintering step (S4), it is preferable to sinter the mixture by adding 3 to 5 parts by weight of binder to 100 parts by weight of the calcined mixture powder at 1,200°C to 1,400°C for 150 to 210 minutes, but it is more preferable to sinter the mixture by adding 3 parts by weight of binder to 100 parts by weight of the calcined mixture powder at 1,300°C for 3 hours.

If the mixing amount of the above binder is less than the above-mentioned limited range, there is a concern that the shape-retaining power may be weakened and the effect as a binder may not be properly implemented, and if it exceeds the above-mentioned limited range, cracks may occur in the sintered body due to carbonization of organic substances during sintering, resulting in a decrease in density. La _0.7 Sr _0.3-x Mg _x MnO ₃ (0.05 ≤ x ≤ 0.2) There is concern that the properties of ceramics may deteriorate.

In addition, if the sintering conditions fall below the above-mentioned limited range, there is a concern that the calcined mixtures may not be sufficiently sintered, and if they exceed the above-mentioned limited range, there is a concern that an inefficient process may be performed due to excessive heat being applied.

The above binder It is preferable that it be a mixture of one or more selected from PVA (polyvinylalcohol), PEG (polyethylene glycol), methyl cellulose, or ethyl cellulose, but it is more preferable to select PVA (polyvinylalcohol).

The above cooling step (S5) is a step of cooling the sintered mixture to room temperature in the air to manufacture La _0.7 Sr _0.3-x Mg _x MnO ₃ , wherein x is preferably 0.05 ≤ x ≤ 0.2.

La _0.7 Sr _0.3-x Mg _x MnO ₃ (0.05 ≤ x ≤ 0.2) manufactured by the manufacturing method of the present invention is characterized by having a room temperature resistivity of 35 Ω-cm to 50 Ω-cm.

In addition, La _0.7 Sr _0.3-x Mg _x MnO ₃ (0.05 ≤ x ≤ 0.2) manufactured by the above manufacturing method is characterized by a B _25/65 integer of 380 K to 400 K, which was calculated by the following mathematical formula 1.

(Mathematical formula 1)

B _25/65 =(lnR ₁ -lnR ₂ )/(1/T ₁ -1/T ₂ )

In the above, B is the thermistor constant, R ₁ and R ₂ are the resistance values at T ₁ (25°C) and T ₂ (65°C), respectively.

Therefore, La _0.7 Sr _0.3-x Mg _x MnO ₃ (0.05 ≤ x ≤ 0.2) manufactured by the above method exhibits a VRH (variable range hopping) conduction mechanism due to the microstructural characteristics of the polycrystalline bulk specimen by adding MgO to the La _0.7 Sr _0.3 MnO ₃ compound having excellent structural and electrical properties, and in particular, The excellent linearity of the electrical resistance with respect to temperature change near room temperature is expected to enable its application as a thermistor material for temperature sensors.

Hereinafter, in order to help understand the present invention, examples will be given and described in detail. However, the following examples are only intended to illustrate the content of the present invention, and the scope of the present invention is not limited to the following examples. The examples of the present invention are provided to more completely explain the present invention to a person having average knowledge in the art.

<Example> Manufacture of La _0.7 Sr _0.3-x Mg _x MnO ₃ ceramics

As shown in Fig. 1, raw materials of La ₂ O ₃ , SrCO ₃ , MgO, and Mn ₂ O ₃ were weighed and mixed according to the composition formula of La _0.7 Sr _0.3-x Mg _x MnO ₃ (0.05 ≤ x ≤ 0.2), and 30 to 50 parts by weight of ethyl alcohol as a dispersion medium was added to 100 parts by weight of the mixture, and then mixed and ground using a zirconia ball mill for 24 hours. The pulverized mixture powder was calcined at 850°C for 2 hours, and 3 parts by weight of PVA (polyvinylalcohol) binder was added to 100 parts by weight of the mixture powder, mixed, and the mixture was sintered at 1,300°C for 3 hours and then cooled to room temperature to produce a La _0.7 Sr _0.3-x Mg _x MnO ₃ (0.05 ≤ x ≤ 0.2) specimen by the solid-state reaction method.

<Experimental Example> Evaluation of La _0.7 Sr _0.3-x Mg _x MnO ₃ Ceramics

The crystallographic properties and microstructure of La _0.7 Sr _0.3-x Mg _x MnO ₃ ceramic specimens were analyzed using X-ray diffraction (XRD, D8, Bruker) and field emission scanning electron microscopy (FE-SEM, XL30S, Philips).

also, La _0.7 Sr _0.3-x Mg _x MnO ₃ (0.05 ≤ x ≤ 0.2) ceramic specimens were polished to a thickness of 0.5 mm, and Ag electrodes were applied to both sides by screen printing. Then, they were heat-treated at 650℃ for 30 minutes. The electrical characteristics according to the composition and temperature change were analyzed using an LCR meter (PM-6036, Fluke) and an electrometer (Keithley 6517A).

In Fig. 2, La _0.7 Sr _0.3-x Mg _x MnO ₃ (0.05 ≤ x ≤ 0.2) manufactured according to an embodiment This figure shows the X-ray diffraction patterns of ceramic specimens according to the amount of Mg ²⁺ added. All specimens showed a polycrystalline rhombohedral crystal structure without preferential orientation. It appears that no deformation of the perovskite crystal structure or unreacted substances were observed according to the amount of Mg ²⁺ added, indicating that a uniform solid solution was formed. In particular, for the sample with Mg = 0.2 mol added, the (110) peak splitting occurred around 2θ = 32°. This is presumed to be due to the coexistence of perovskite structures of (La,Sr)MnO ₃ -type and (La,Mg)MnO ₃ -type. In the case of Fig. 1(b), which is an enlarged image of the X-ray diffraction angle around 32–33°, the diffraction peak tended to shift to a higher angle as the amount of Mg ²⁺ added increased. This is presumed to be due to a decrease in the interplanar spacing due to the distortion of the unit cell as Mg ²⁺ (0.089 nm), which has a small ionic radius, is substituted for Sr ²⁺ (0.144 nm).

Figure 3 is a La _0.7 Sr _0.3-x Mg _x MnO ₃ (0.05 ≤ x ≤ 0.2) manufactured according to an embodiment. The surface microstructure of ceramic specimens according to the amount of Mg ²⁺ added is shown in the SEM photograph (magnification x 20,000). Pores were observed in all specimens, and a granule-shaped microstructure with an average grain size of less than 1 ㎛ was shown. As the amount of Mg ²⁺ added increased, the average grain size slightly increased, and the pores showed a characteristic of decreasing. This is presumed to be due to the increase in the contact area of the particles during sintering of the specimen due to the addition of MgO (mp = 922 K), which has a low melting point.

La _0.7 Sr _0.3-x Mg _x MnO ₃ (LSMMO) (0.05 ≤ x ≤ 0.2) manufactured according to the embodiment As shown in Fig. 4, the room temperature resistivity of the ceramic specimens according to the amount of Mg ²⁺ added showed a tendency for the resistivity to gradually decrease as the amount of Mg added increased. The magnetic and electrical properties of (La,Sr)MnO ₃ ^{(LSMO) are affected by the double exchange interaction of the outermost electrons as some of the Mn 3+ ions change to Mn 4+ ions to} compensate for the non-uniformity of charges within the unit cell due to the substitution of Sr ²⁺ for La 3+ .

In particular, the electrical resistance is sensitively affected by the lattice deformation caused by the Jahn-Teller distortion of oxygen octahedral MnO6 due to the addition of Sr ²⁺ (0.144 nm), which has a large ionic radius, to La ³⁺ (0.136 nm) and by the hopping conduction between Mn ³⁺ and Mn ⁴⁺ ions mediated by oxygen ions.

In the present invention, it is estimated that the resistivity is reduced due to the offset of the distortion of the perovskite unit cell by substituting Mg ²⁺ (0.089 nm) with a small ionic radius for Sr ²⁺ of the LSMMO composition and the increase in the hopping probability due to the increase in the bonding angle between Mn ³⁺ -O-Mn ⁴⁺ .

Figure 5 shows the electrical resistance of La _0.7 Sr _0.3-x Mg _x MnO ₃ (LSMMO)(0.05 ≤ x ≤ 0.2) specimens according to the amount of Mg ²⁺ added and the temperature. All specimens showed a characteristic of linearly decreasing electrical resistance as the temperature increased. This is presumed to be because the conductivity increased as the charges trapped in the crystal grains, grain boundaries, pores, and lattice defects in the polycrystalline specimen were excited by thermal stimulation, as observed in the microstructure of Figure 2.

The temperature coefficient of resistance [temperature coefficient of resistance, TCR (α) = (1/RT)(dRT/dT); RT is the resistance value at T(℃)] showed no dependence on the amount of Mg added, and exhibited good characteristics of 0.37 to 0.38%/℃.

The B _25/65 constant of La _0.7 Sr _0.3-x Mg _x MnO ₃ (LSMMO)(0.05 ≤ x ≤ 0.2) specimens according to the amount of Mg ²⁺ added is shown in Fig. 6. The B _25/65 constant is an inherent characteristic of a material that indicates the sensitivity of the change in electrical resistance according to temperature, and was calculated using the mathematical equation 1 above.

As the amount of Mg added increased, the B constant gradually increased. This is thought to be due to the increase in grain size, the decrease in pores, and the decrease in carrier scattering due to the somewhat alleviation of distortion within the perovskite unit cell by the addition of Mg ²⁺ , which has a larger ionic radius than Sr ²⁺ , to the polycrystalline LSMO sample. The sample with 0.20 mol of Mg ²⁺ added showed good B _25/65 constant characteristics at 394 K.

The conduction phenomenon of perovskite LSMO is affected by Jahn-Teller distortion and hopping conduction depending on the Mg-O bond distance and Mg-O-Mg bond angle, and the temperature-dependent electrical conductivity is generally expressed by the following mathematical equation 2.

(Mathematical formula 2)

In the above mathematical expression 2, R is the resistance, C ₀ is a constant, T is the temperature, and T ₀ is the characteristic temperature.

For nearest neighbor hopping (NNH) conduction, α = ρ = 1, and for variable range hopping (VRH) conduction, α = 4ρ.

Figure 7 shows the ln (R T ^-1 ) vs 1/T ^1/4 curves of La _0.7 Sr _0.3-x Mg _x MnO ₃ (LSMMO)(0.05 ≤ x ≤ 0.2) specimens according to the amount of Mg ²⁺ added. The specimen with 0.05 mol of Mg ²⁺ added exhibited good linearity over the measurement temperature range, and the slope in the high temperature region increased as the amount of Mg ²⁺ added increased.

This is believed to be due to the distribution of various space charges caused by the crystal grains, grain boundaries, and pores of the polycrystalline bulk specimen, and the rapid increase of carriers due to thermal stimulation as the temperature increases.

In this way, in the present invention, La _0.7 Sr _0.3-x Mg _x MnO ₃ (LSMMO)(0.05 ≤ x ≤ 0.2) All specimens containing Mg ²⁺ added to the ceramics exhibited a polycrystalline rhombohedral crystal structure without preferential orientation, and it was confirmed that the diffraction peaks tended to shift to high angles as the amount of Mg ²⁺ added increased. In addition, the room temperature resistivity tended to decrease gradually as the amount of Mg ²⁺ added increased. This is presumed to be due to the decrease in unit cell distortion resulting from the substitution of Mg ²⁺ with a smaller ionic radius for Sr ²⁺ .

While the specific parts of the present invention have been described in detail above, it is obvious to those skilled in the art that such specific descriptions are merely preferred implementation examples and that the scope of the present invention is not limited thereto. Accordingly, the actual scope of the present invention will be defined by the appended claims and their equivalents. The scope of the present invention is indicated by the claims set forth below, and all changes or modifications derived from the meaning and scope of the claims and their equivalent concepts should be interpreted as being included in the scope of the present invention.

Claims (11)

Step (S1) of mixing raw materials of La ₂ O ₃ , SrCO ₃ , MgO, and Mn ₂ O ₃ ;
A step (S2) of adding a dispersant to the above mixed raw materials and pulverizing the mixture;
Step (S3) of calcining the above-mentioned pulverized mixture for solid-state reaction;
Step (S4) of mixing a binder into the above-mentioned mixture powder and sintering it; and
A method for manufacturing Mg-doped La _0.7 Sr _0.3-x Mg _x MnO ₃ ceramics, characterized by including a step (S5) of cooling the sintered mixture.
In the first paragraph,
A method for manufacturing Mg-doped La _0.7 Sr _0.3-x Mg _x MnO ₃ ceramics, characterized in that in the above raw material mixing step (S1), raw materials La ₂ O ₃ , SrCO ₃ , MgO, and Mn ₂ O ₃ are mixed by stoichiometrically weighing them according to the composition formula of La _0.7 Sr 0.3- _x Mg _x MnO ₃
In the second paragraph,
A method for manufacturing Mg-doped La _0.7 Sr _0.3-x Mg _x MnO ₃ ceramics, characterized in that in the above La _0.7 Sr _0.3-x Mg _x MnO ₃ , x is 0.05 ≤ x ≤ 0.2.
In the first paragraph,
A method for manufacturing Mg-doped La _0.7 Sr _0.3 -x Mg x MnO 3 ceramics, characterized in that in the mixture grinding step ( _S2 ), 30 to 50 parts by weight of a dispersion medium is mixed with 100 parts by weight of the mixture, and then mixing and grinding is performed for 22 to ₂₆ hours using a zirconia ball mill.
In paragraph 4,
A method for manufacturing Mg-doped La _0.7 Sr _0.3-x Mg _x MnO ₃ ceramics, characterized in that the dispersion medium is one or more mixed solvents selected from methanol, ethanol, isopropyl alcohol, acetone, and distilled water.
In the first paragraph,
A method for producing Mg-doped La _0.7 Sr _0.3-x Mg _x MnO ₃ ceramics, characterized in that in the above calcination step (S3), the pulverized mixture is calcined at 840°C to 860°C for 110 to 130 minutes.
In the first paragraph,
A method for manufacturing Mg-doped La 0.7 Sr 0.3-x Mg x MnO 3 ceramics, characterized in that in the sintering step (S4), 3 to _{5 parts} by weight of a binder is added to 100 parts by weight of a calcined mixture powder, and the resulting mixture is sintered at _1,200 °C to _1,400 °C for 150 to 210 minutes.
In Article 7,
A method for manufacturing Mg-doped La _0.7 Sr _0.3-x Mg x MnO 3 ceramics, characterized in that the binder is a mixture of one or more selected from PVA (polyvinylalcohol), PEG (polyethylene glycol), methyl cellulose, _{and ethyl} cellulose.
In the first paragraph,
A method for manufacturing Mg-doped La _0.7 Sr _0.3-x Mg _x MnO ₃ ceramics, characterized in that in the above cooling step (S5), the sintered mixture is cooled to room temperature.

Among the methods for manufacturing Mg-doped La _0.7 Sr _0.3-x Mg _x MnO ₃ ceramics according to claims 1 to 9, Mg-doped La _0.7 Sr _0.3-x Mg _x MnO ₃ ceramics characterized in that La _0.7 Sr _0.3-x Mg _x MnO ₃ (0.05 ≤ x ≤ 0.2) is manufactured by any one of the methods.
In Article 10,
The above ceramics are Mg-doped La _0.7 Sr _0.3-x Mg _x MnO ₃ ceramics, characterized in that the room temperature resistivity is 35 Ω-cm to 50 Ω-cm and the B _25/65 integer is 380 K to 400 K.