CN100434365C - YBa2Cu3O7 multicrystal nano-wire array and its preparation method - Google Patents

Abstract

The YBa ₂ Cu ₃ O ₇ nanowire ordered array and the preparation method thereof in the present invention are characterized in that the complexing agent ethylenediaminetetraacetic acid and the cross-linking agent ethylene glycol are used, and ethylene glycol with a pH of 7-8 and a molar concentration of 0.6-1.2 is used. Amine tetraacetic acid aqueous solution, according to Y:Ba:Cu molar ratio 1:2:3, add Y _{( NO 3 ) 3} and Cu(NO ₃ ) ₂ mixed solution and Ba(NO ₃ ) ₂ powder, so that the molar weight of ethylenediaminetetraacetic acid contained is twice that of CuO; add ethylene glycol and heat to obtain a dark brown sol solution; inject it into the porous rice hole obtained by the secondary anodic oxidation method under low vacuum In the alumina template, after sintering and annealing in a pure oxygen atmosphere, an ordered array of polycrystalline YBa ₂ Cu ₃ O ₇ nanowires with a diameter of 50-60 nm and a length of micron scale, arranged in parallel to each other, can be obtained in the porous alumina template , whose crystal lattice is an orthorhombic structure, possessing high-temperature superconductivity.

Description

YBa2Cu3O7 polycrystalline nanowire array and its preparation method

Technical field:

The invention belongs to the technical field of oxide high-temperature superconducting materials and their preparation, and in particular relates to an ordered array of YBa ₂ Cu ₃ O ₇ high-temperature superconducting material nanowires and a preparation method thereof.

Background technique:

The American journal "Physical Review Letters" (1987, volume 58, page 908) reported for the first time the YBa ₂ Cu ₃ O _7-δ oxide high-temperature superconductor, with a superconducting transition temperature of 93K, which is the first high-temperature superconductor. Oxide superconductors at liquid nitrogen temperatures. At present, the methods for preparing Y-Ba-Cu-O system high-temperature superconducting materials are mainly ceramic sintering method and organic metal salt chemical vapor deposition method. For example, the solid-phase reaction method reported in "Journal of the American Chemical Society" (1998, volume 120, page 2733), the sol-gel method reported in the journal "Superconducting Technology" (2003, volume 16, page 1202) Method, the coprecipitation method of U.S. " Applied Physics Letters " magazine (1991, volume 120, the 2426th page) report, the chemical vapor deposition method of German " advanced material " magazine (2000, 12 volumes, the 116th page) report. The existing solid phase reaction method and co-precipitation method are limited by their raw materials and preparation methods, and their products can only be random powders in the order of microns and nanometers, and require a high sintering temperature; chemical vapor deposition method Due to the reasons of equipment and process, most of the products are thin films, and the method is complicated and expensive, which is not conducive to popularization and application.

One-dimensional and quasi-one-dimensional nanomaterials have been widely studied because of their unique properties, and ordered arrays of nanowires have many exotic properties and broad application prospects. At present, ordered nanowire arrays of many metals, alloys, oxides and ferrite materials have been successfully synthesized, for example: American Chemical Society "Nano Letters" magazine (2003, volume 3, page 919) reports A series of metal nanowire arrays such as Au, Ag, Cu, etc., the Ni-Cu alloy nanowire array reported by the American Chemical Society "Chemical Materials" (2003, Volume 15, page 664), German "Applied Physics A" magazine (2003, vol. 78, p. 1197) reported Fe ₂ O ₃ nanowire arrays. But so far there is no report on the preparation of ordered arrays of high-temperature superconducting material YBa ₂ Cu ₃ O ₇ nanowires.

Invention content:

The invention provides a high-temperature superconducting material YBa ₂ Cu ₃ O ₇ nanowire ordered array and a preparation method thereof.

The preparation method of the YBa ₂ Cu ₃ O ₇ nanowire ordered array of the present invention is characterized in that: take an aqueous solution of ethylenediaminetetraacetic acid with a pH value of 7-8 and a molar concentration of 0.6-1.2M, according to Y:Ba: The molar ratio of Cu is 1:2:3, and the mixed solution of Y(NO ₃ ) ₃ and Cu(NO ₃ ) ₂ obtained by dissolving Y ₂ O ₃ and CuO in nitric acid and Ba(NO ₃ ) ₂ powder are added to make the contained The molar weight of ethylenediaminetetraacetic acid is twice that of CuO; add ethylene glycol 1-3 times the volume of the solution, and heat until the system changes from a blue solution to a dark brown sol solution; put aluminum with a purity of not less than 99.9% After the sheet is annealed for 4-7 hours in an environment with a vacuum degree of not less than 10 ^-3 Pa and a temperature of 500-600 ° C, it is placed at the anode of an electrolytic cell filled with 0.3M ± 0.05M oxalic acid electrolyte, so that the aluminum One side of the sheet is in contact with the electrolyte, the other side is in contact with the anode copper sheet, corroded for 8-10 hours at 30-45V, 0-5°C, and the corroded aluminum sheet is placed in 6±1wt% phosphoric acid and 1.5±0.5wt% % chromic acid mixed acid solution, soaked at 40-60 ℃ for 10-20 hours, and then put the aluminum sheet on the anode of the electrolytic cell with 0.3±0.05M oxalic acid solution, and the corroded side and the electrolytic Liquid contact, the other side is in contact with the anode of the copper sheet, and the second corrosion is carried out at 30-45V, 0-5°C for 18-24 hours; the side that is not in contact with the electrolyte is removed with a solution that can undergo a displacement reaction with aluminum The remaining aluminum layer; place the face that has been removed from the aluminum downward, and float on the 4-6wt% phosphoric acid solution for 2-4 hours to make holes; place the porous alumina template after the holes in the above-mentioned sol solution, and evacuate to no lower than 10 ^-1 Pa; take out the porous alumina template filled with sol, and keep it at 700-800°C for more than 10 hours to obtain an ordered array of YBa ₂ Cu ₃ O _7-δ nanowires contained in the template; An annealing treatment in a pure oxygen atmosphere can obtain an ordered array of YBa ₂ Cu ₃ O ₇ nanowires.

The solution capable of undergoing a replacement reaction with aluminum to remove the remaining aluminum layer on the side not in contact with the electrolyte includes CuCl ₂ or SnCl ₂ .

The ordered array of YBa ₂ Cu ₃ O ₇ nanowires prepared by the above method in the present invention is characterized in that it is polycrystalline YBa ₂ Cu ₃ O arranged in parallel to each other contained in a porous alumina template with a pore size of 50-60 nm. An ordered array composed of ₇ nanometer wires, the lattice is an orthogonal structure, and has high-temperature superconductivity.

The method in the present invention utilizes ethylenediaminetetraacetic acid as a complexing agent, and ethylene glycol as a crosslinking agent to obtain a uniform and stable sol. The equipment used is simple and easy to operate; controlling the heating rate and time can regulate ethylene glycol and ethylene glycol The speed and degree of the polymerization reaction of amine tetraacetic acid can grasp the sol-gel transition process; the viscosity of the sol can be adjusted to perfuse alumina templates with different pore sizes, so that nanowires with different diameters can be obtained; since alumina starts at 800 ° C Crystallization, the crystallized alumina is insoluble in acid and alkali, so the obtained nanowires cannot be processed for characterization, so the upper limit of the sintering temperature is 800°C; traditional sol-gel preparation methods mostly use organometallic salts as precursors It is expensive, complicated to operate, and cannot effectively control the transformation process of sol-gel, and cannot realize the regulation of the viscosity of the sol, so that the sol obtained by the traditional method is not suitable for perfusion of porous alumina templates to prepare nanowires; and the traditional solid-state reaction Compared with the synthetic temperature of the co-precipitation method being above 900°C, the sol precursor in the method of the present invention is a molecular-level uniform mixing system, and the reaction activation energy is greatly reduced, so that the temperature of the synthesis of YBa ₂ Cu ₃ O ₇ by the method of the present invention is reduced to 700°C ℃; the traditional solid-state reaction method can only obtain micron-sized random particle powder, but in the method of the present invention, a large-area nanowire ordered array can be obtained by using a porous alumina template as a hard template constraint. This method is currently known in the world as a relatively simple, cheap, and easy method for synthesizing an ordered array of high-temperature superconducting material YBa ₂ Cu ₃ O ₇ nanowires.

YBa ₂ Cu ₃ O ₇ in the present invention is an ordered array of nanowires composed of polycrystalline compounds with a diameter of 50-60nm and parallel and vertical arrangements. It is the first time in the world to successfully synthesize a large-area, dense, continuous and The ordered array of YBa ₂ Cu ₃ O ₇ one-dimensional nanowires with high-temperature superconducting properties is conducive to further understanding the origin of high-temperature superconductivity, for the development of high-sensitivity infrared detection devices, Josephson Festival ultra-high-speed computers, and high-resolution superconductivity Quantum interferometers provide an important material basis.

Description of drawings:

Figure 1 is a photo of the surface morphology of the porous alumina template observed by the JSM-6700F field emission scanning electron microscope (FE-SEM);

Figure 2 is a photo of the cross-sectional morphology of the porous alumina template observed by the JSM-6700F field emission scanning electron microscope.

Fig. 3 is a copper target X-ray diffraction pattern diagram of a YBa ₂ Cu ₃ O _7-δ nanowire array filled in a porous alumina template.

Figure 4 is a photo of the surface morphology of the nanowire array contained in the porous alumina template observed by the JSM-6700F field emission scanning electron microscope;

Figure 5, Figure 6 and Figure 7 are photos of the surface topography of the YBa ₂ Cu ₃ O _7-δ nanowire array at different magnifications observed by the JSM-6700F field emission scanning electron microscope after removing part of the alumina template.

Fig. 8 is a photograph of the morphology of YBa ₂ Cu ₃ O _7-δ nanowires observed by H-800 transmission electron microscope (TEM) after removing all the alumina templates.

Fig. 9 is a single YBa ₂ Cu ₃ O _7-δ nanowire and its corresponding selected area electron diffraction pattern observed by JEOL-2010 high-resolution transmission electron microscope (HRTEM).

Fig. 10 is a graph showing the relationship between magnetization and temperature of YBa ₂ Cu ₃ O ₇ nanowire arrays measured on a superconducting quantum interference device (SQUID).

Detailed ways:

Example 1: Preparation of ordered array of YBa ₂ Cu ₃ O ₇ nanowires

1) Preparation of porous alumina template by secondary anodic oxidation method:

Put the aluminum sheet with a purity of not less than 99.9% (the purity of the aluminum sheet used in this example is 99.999%) through ultrasonic cleaning, polishing and annealing into the electrolytic cell, using 0.3mol/L oxalic acid as the electrolyte, At a temperature of 0--5°C, apply an oxidation voltage of 40V for primary oxidation for 8-10 hours; soak the aluminum sheet after primary oxidation in a mixed acid composed of H ₃ PO4 and H ₂ CrO ₄ for 10-20 hours Then take it out, and carry out secondary oxidation for 20 hours under the same conditions as the primary oxidation; seal one side of the oxide film of the aluminum sheet after secondary oxidation, and immerse the other side in 1mol/L CuCl ₂ solution until no Take out when air bubbles are generated to remove the aluminum matrix on this side;

Its chemical process can be expressed as:

2Al+3CuCl ₂ →3Cu+2AlCl ₃

Finally, the aluminum sheet is floated in 5±1wt% phosphoric acid solution until water droplets seep out from the upper surface. This step is used to remove the barrier layer of the aluminum oxide film.

2), the sol solution required for preparation by sol-gel method:

According to the composition of compound YBa ₂ Cu ₃ O ₇ , weigh 0.4516g (0.002mol) Y ₂ O ₃ , 2.0904g (0.008mol) Ba(NO ₃ ) ₂ , 0.9546g ( _0.012mol ) CuO; ₃ and CuO were dissolved in HNO ₃ solution to obtain 20ml of a mixed solution of Y(NO ₃ ) ₃ and Cu(NO ₃ ) ₂ ; weigh 7.02g (0.024mol) ethylenediaminetetraacetic acid, dissolve it in 30ml of distilled water, and use Adjust the pH value to 7-8 with ethylenediamine; add Ba(NO ₃ ) ₂ that has been weighed and stir until it is completely dissolved; pour the above 20ml mixed solution of Y(NO ₃ ) ₃ and Cu(NO ₃ ) ₂ , and add ethylenediamine to neutralize excess nitric acid in the process of dissolving Y ₂ O ₃ and CuO to keep the pH value of the solution at 7-8, stir to obtain a uniform and stable blue solution; add 50ml of - 150ml of ethylene glycol and stirring to make it uniformly mixed with the solution, and heating the obtained mixed solution for 40-60 minutes to obtain a uniform and stable sol solution of brown color. The greater the volume of ethylene glycol, the greater the viscosity of the obtained sol solution and the less heating time required.

3), Preparation of YBa ₂ Cu ₃ O ₇ nanowire arrays:

Submerge the porous alumina template in the jar containing the sol solution prepared in step 2, and keep it for 10-30 minutes under the condition that the vacuum degree is not lower than 10 ^-1 Pa; fill the holes with the alumina of the sol solution After the template is incubated in air at 700° C. for 12 hours, an ordered array of YBa ₂ Cu ₃ O _7-δ nanowires filled in the holes of the alumina template is obtained.

4), sample processing

First use tweezers to take a cotton ball dipped in a small amount of absolute ethanol and gently wipe the surface of the template, and then use a cotton ball to dip a small amount of Al ₂ O ₃ ultrafine powder to wipe the surface of the template for 5-10 minutes to remove the YBa ₂ Cu adhered to the surface ₃ O _7-δ powder, and then use small tweezers to separate the aluminum oxide film from the surrounding aluminum substrate; grind 8-10 alumina templates that have been treated above into powder for XRD testing. In a pure oxygen atmosphere, the procedure is as follows: After 30 hours of heating from 300°C to 500°C, and then 30 hours of annealing treatment from 500°C to 300°C, the magnetization can be measured on a superconducting quantum interference instrument (SQUID). The relationship curve with temperature.

FE-SEM, TEM, and HRTEM tests can be carried out after the alumina templates that have been wiped on the surface and filled with YBa ₂ Cu ₃ O _7-δ nanowires are corroded to varying degrees with 6mol/L NaOH solution.

Figure 1 is the FE-SEM image of the surface of the self-made porous alumina template. It can be seen from the figure that the holes of the prepared porous alumina template have uniform diameter, regular shape and highly ordered arrangement;

Figure 2 is a cross-sectional FE-SEM image of the porous alumina template. It can be seen from the figure that the pores of the prepared porous alumina template are vertical to the membrane surface and arranged parallel to each other.

Fig. 3 is the X-ray diffraction pattern after grinding the aluminum oxide template filled with YBa ₂ Cu ₃ O _7-δ nanowire arrays prepared in the example, the abscissa is the diffraction angle (2θ), and the ordinate is is the relative diffraction intensity; all the diffraction peaks in the figure are consistent with JCPDS-89-5842 in the international standard powder XRD diffraction card, and can be converted into (103), (102), (103), (110) according to the orthogonal lattice index ...Since the alumina template used in this example is an oxygen-deficient structure, the YBCO samples fired in a general air atmosphere will show different degrees of oxygen-deficient structures, and the result indicators in Figure 3 Chloride YBa ₂ Cu ₃ O _6.94 is an oxygen-deficient structure. Annealing the sample in a pure oxygen atmosphere can obtain YBCO nanowires without oxygen deficiency, that is, YBa ₂ Cu ₃ O ₇ nanowires.

Figure 4 is the FE-SEM image of the surface observed after wiping off the attachments on the surface of the alumina template filled with YBa ₂ Cu ₃ O _7-δ nanowires. This figure intuitively reflects that high filling can be obtained by using the method in the embodiment rate of YBa ₂ Cu ₃ O _7-δ nanowire arrays, which is consistent with the results in Fig. 4 and Fig. 5.

Figure 5, Figure 6 and Figure 7 are FE-SEM images of different magnifications of the YBa ₂ Cu ₃ O _7-δ nanowire array after removing part of the alumina template, and Figure 4 and Figure 5 reflect the method used in the embodiment The prepared nanowire has a large area, and its filling rate is very high; Figure 6 shows that the prepared nanowire has the characteristics of fullness, uniform diameter, and relatively large length and diameter, and its length is on the order of microns.

Figure 8 is the TEM morphology image observed after removing all the alumina templates. It can be seen from the figure that the YBa ₂ Cu ₃ O _7-δ nanowires prepared by the method in practice have uniform diameter, smooth surface and nanowire Relatively dense, the length is on the order of microns.

Figure 9 is the topography of a YBa ₂ Cu ₃ O _7-δ single nanowire and its corresponding selected area electron diffraction pattern observed by a high-resolution transmission electron microscope (HRTEM). This figure further proves that the diameter of the nanowire is uniform, The surface is smooth and dense; its electron diffraction pattern is ring-shaped, which proves that the prepared YBa ₂ Cu ₃ O ₇ nanowires are polycrystalline, and can be indexed into (104), (020), (205) crystal planes. It is consistent with the XRD index results.

Figure 10 is a graph showing the relationship between the magnetization and temperature of the YBa ₂ Cu ₃ O ₇ nanowire array annealed in a pure oxygen atmosphere measured by a superconducting quantum interferometer. It can be seen that the sample exhibits diamagnetism below 91.8K; The book "Superconducting Physics" (Zhang Liyuan, Zhang Jinlong, p. 7, Electronic Industry Press) mentions that the surface shielding current surrounding the high-temperature superconductor causes the diamagnetism of the entire system; this is a characteristic of high-temperature superconductor materials One, the magnetic measurement result in this embodiment is that the system exhibits diamagnetism in the range of 10-91.8K, indicating that the shielding current of the system has been established at this time, and the superconductor has no resistance below the superconducting transition temperature (T _c ), The shielding current will always exist, so the samples in the examples will show diamagnetism at temperatures lower than 91.8K, which is consistent with the reported superconducting transition temperature of YBa ₂ Cu ₃ O ₇ bulk materials.

The measurement results of XRD, FE-SEM, TEM, HRTEM, SQUID and literature search show that: the high temperature superconducting material YBa ₂ Cu ₃ O ₇ polycrystalline nanowire ordered array was successfully prepared for the first time by adopting the method of the present invention, and the required equipment of the method The method is simple and the cost is low; the ordered array of YBa ₂ Cu ₃ O ₇ polycrystalline nanowires prepared has superconductivity, and has a certain role in promoting the further understanding of the mechanism of high-temperature superconductivity and the development and application of nanometer devices.

Claims (3)

1, a kind of YBa ₂Cu ₃O ₇The preparation method of nanometer line ordered array is characterized in that: getting the pH value is the edta solution of 0.6-1.2M for 7-8, volumetric molar concentration, and by Y: Ba: the Cu mol ratio is that adding in 1: 2: 3 is by nitric acid dissolve Y ₂O ₃Y (the NO that obtains with CuO ₃) ₃And Cu (NO ₃) ₂Mixing solutions and Ba (NO ₃) ₂Powder, the molar weight that makes wherein contained ethylenediamine tetraacetic acid (EDTA) is the twice of CuO; Add this liquor capacity 1-3 ethylene glycol doubly, the system that is heated to becomes the Vandyke brown sol solution by blue solution; Purity is not less than 99.9% aluminium flake and is not less than 10 in vacuum tightness ^-3Pa, temperature is annealing after 4-7 hour in 500-600 ℃ the environment, place the electrolyzer anode place of the oxalic acid electrolytic solution that 0.3M ± 0.05M is housed, the one side of aluminium flake is contacted with electrolytic solution, another side contacts with the anode copper sheet, at 30-45V, corrosion is 8-10 hour under the 0-5 ℃ of condition, aluminium flake after the corrosion is placed in the mixed acid solution of 6 ± 1wt% phosphoric acid and 1.5 ± 0.5wt% chromic acid composition, soaked 10-20 hour at 40-60 ℃, then this aluminium flake is placed on the anode place of the electrolyzer that 0.3 ± 0.05M oxalic acid solution is housed, the one side that was corroded is contacted with electrolytic solution, another side contacts with the copper sheet anode, at 30-45V, carried out corroding the second time 18-24 hour under the 0-5 ℃ of condition; With removing the remaining aluminium lamination of the side that does not contact with the solution of aluminium generation replacement(metathesis)reaction with electrolytic solution; To face down except that this of intact aluminium, float on 2-4 hour through hole on the 4-6wt% phosphoric acid solution; Porous alumina formwork behind the through hole is placed above-mentioned sol solution, be evacuated to and be not less than 10 ^-1Pa; Take out the porous alumina formwork that this has filled colloidal sol, more than 10 hours, obtain being included in the YBa in the template 700-800 ℃ of insulation ₂Cu ₃O _7-δNanometer line ordered array; Through the pure oxygen atmosphere anneal, promptly obtain YBa again ₂Cu ₃O ₇Nanometer line ordered array.

2, YBa according to claim 1 ₂Cu ₃O ₇The preparation method of nanometer line ordered array is characterised in that described energy comprises CuCl with aluminium generation replacement(metathesis)reaction with the solution of removing the side residue aluminium lamination that does not contact with electrolytic solution ₂Or SnCl ₂

3, adopt the YBa of the described method preparation of claim 1 ₂Cu ₃O ₇Nanometer line ordered array is characterised in that it is to be contained in polycrystalline YBa in the porous alumina formwork that the aperture is 50-60nm, that be arranged parallel to each other ₂Cu ₃O ₇The oldered array that nano wire is formed, lattice is an orthohormbic structure, it is electrical to possess high-temperature superconductor.

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