KR910001306B1 - Superconductive compound of k2nif4 structural type having high transition temperature and method for fabricating same - Google Patents

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Superconducting Compound of K2NiF4 Structure with High Transition Temperature and Its Manufacturing Method

1 is a representative circuit diagram used by measuring the dc conductivity of a superconductor having a high Tc (critical temperature) of the present invention.

2 shows X (Ba) = 1 (two upper curves, left scale) and X (Ba) = 0.75 (lower curve, right scale) for composition Ba _x La _5-x Cu ₅ O _{5 (3-y)} . Shows the effect of temperature correlation resistance and residual density flowing through the composition on a sample having:

3 shows low temperature correlation resistance for different annealing conditions (ie, temperature and partial pressure of oxygen) for compositions Ba _x La _5-x Cu ₅ O _{5 (3-y)} with X (Ba) = 1.

4 shows the low temperature resistance of composition Ba _x La _5-x Cu ₅ O _{5 (3-y)} with X (Ba) = 0.75 measured for different current densities flowing through the composition.

The present invention relates to a novel class of superconductors, in particular components of the K ₂ NiF ₄ structure with superconductor properties under relatively high transition temperatures and methods of preparing these compounds.

Superconductivity is usually defined as the complete loss of electrical resistance of a material at defined temperatures. This phenomenon is known to occur in many materials. About one quarter of the elements, and more than 1000 alloys and components, have been found to be superconductors. Superconductivity is considered to be a property of materials in the metallic state, and all known superconductors are metallic under the conditions of superconducting them. Some conventional non-metallic materials become superconducting under very high pressures, for example, before they become superconductors and convert them into metal.

Superconductors are strong magnet coil-forming materials for use in connection with plasma and nuclear physics, nuclear resonance medical diagnostics, and magnetic levitation of high-speed trains. In the case of transportation, it is a very interesting material. For example, generating power by atomic fusion requires a very large magnetic field that can only be provided by superconducting a magnet. Superconductors also find application in computers and high-speed signal processing and data communications. The advantages of superconductors are quite obvious, but the common disadvantage of all the superconducting materials known so far is a very low transition temperature (commonly referred to as "critical temperature": Tc), which is almost similar to low Kelvin (absolute temperature: ° K). Is in. The element with the highest Tc is niobium (9.2 ° K) and the highest known Tc is 23 ° K for Nb ₃ Ge at atmospheric pressure. Thus, most known conductors require liquid helium for cooling and also sophisticated techniques and require significant investment in cost and energy as a major problem.

Therefore, it is an object of the present invention to propose a method for preparing a composition for a high Tc superconductor and a compound having a high critical temperature such that it does not need to be cooled with liquid helium to significantly reduce the required cost and save energy. .

The present invention relates to novel compositions that exhibit superconductivity at temperatures higher than those in previously known superconductor materials, and to methods of using and preparing these compositions. These compositions are capable of flowing a superconducting current (i.e., current in the composition with almost zero resistance) at temperatures above 26 ° K. Typically, this composition is characterized as a mixed transition metal oxide system in that the transition metal oxide can exhibit multifunctional action. These modifiers contain layer-type crystalline structures, often ash titanium, and may contain rare earth or rare earth elements. Rare earth elements (sometimes called elements close to rare earth elements) are elements that have the property of making themselves rare earth elements. For example, it is a group IIIB element of the periodic table such as La. The rare earth (or rare earth) moiety or transition metal moiety in the composition may be substituted. For example, the clay site may contain alkaline earth elements selected from the group IIA of the periodic table, or a combination of rare earth or rare earth elements and alkaline earth elements. Examples of suitable alkapito elements are Ca, Sr and Ba. The transition metal moiety may contain a transition metal exhibiting mixed valence action and may contain one or more transition metals. Particularly good examples of suitable transition metals are copper. As will be apparent below, the copper oxide base system provides unique and excellent properties as a high Tc superconductor.

An example of a superconducting composition having a high Tc is a composition of the general formula RE-TM-O, where RE is a histo or rare earth element, TM is a nonmagnetic transition metal and O is oxygen. Examples of transition metal elements include Cu, Ni, and Cr. In particular, transition metals which can exhibit a polyvalent state are very suitable. Rare earth elements are typically elements 58 to 71 of the periodic table, including Ce, Nd and the like. If alkaline earth elements (AE) are also present, the composition is represented by the general formula RE-AE-TM-O.

The ratio of (AE, RE): TM is about 1: 1 in total, but the ratio of (AE, RE): TM can be varied as can be seen by example when the ratio of 2: 1. Of course, the amount of oxygen present in the final composition can be adjusted to the processing conditions and is such that the valence conditions of the system are satisfied.

Processes capable of preparing the superconducting compositions of the present invention include known ceramics, including mixing rare earth or rare earth, alkaline earth and powders containing transition metal atoms, coprecipitation of these materials and heating in oxygen or air. The principle of manufacture can be used.

A particularly suitable superconducting material according to the invention is one containing copper as the transition metal. Copper may be present in Cu ²⁺ or Cu ³⁺ mixed valence state. The state assumed by copper in the overall composition depends on the amount of oxygen present and the particular substituents on the crystalline structure. Very high Tc was found in copper oxide systems exhibiting mixed valence states, as indicated by conductivity and other measurements. Copper oxide systems containing rare earth or rare earth elements and alkaline earth elements are the only examples of superconducting-multilayered copper oxides having a Tc higher than 26 ° K and a common class.

The present invention proposes the use of compounds having a layer-type structure of a kind known from potassium nickel fluoride K ₂ NiF ₄ . This structure is particularly present as an oxide of the conventional composition RE ₂ TMO ₄ , wherein RE represents a rare earth element (lanthanoid element and TM represents a so-called transition metal). It is a feature of the present invention that the RE moiety in the compound is partially substituted by a combination of metals of one alkaline earth group or elements of an alkali group and lacks oxygen content.

These compounds have the usual composition RE _2-x AE _x TMO _4-y (x <0.3 and y <0.5). Also preferred are the ranges x <0.3 and 0.1 ≦ y ≦ 0.5.

Superconducting compositions of the invention are typically transition metal oxides having mixed valences and layer-like crystalline structures, and exhibit a Tc higher than that of known superconducting materials. These compositions may also contain rare earth sites in layer-like structures, where rare earth and rare earth atoms, and alkaline earth substituents (eg, Ca, Sr and Ba) may be present. Oxygen may be present in an amount to satisfy the valence conditions of the system, and the amount of oxygen depends somewhat on the function of the processing steps used to make the superconducting composition. Oxygen may be present in these compositions in non-stoichiometric amounts. The valence state of the element in oxide form is measured as the final product in a manner well known to chemists. For example, the transition metal Cu may be present in both Cu ²⁺ and Cu ³⁺ states in some compositions.

An example of a superconducting compound having a layer-shaped structure according to the present invention is an oxide of the usual composition RE ₂ TMO ₄ wherein RE represents a rare earth (lanthanide) or rare earth element and TM represents a transition metal. In these compounds, the RE site may be partially substituted with one or more elements of alkaline earth groups. In these specific compounds, the oxygen content is insufficient.

One compound consistent with the above description is lanthanum copper oxide La ₂ CuO ₄ [wherein La belonging to group IIIB element is one neighboring group of IIA element, ie alkaline earth metal such as barium, (or group IIA element) Partly substituted). In addition, the oxygen content of the compound is insufficient for the compound to have a composition of La _2-x , Ba _x CuO _4-y (where x≤0.3 and y <0.5).

Another compound conforming to the general formula given above is lanthanum nickel oxide of the general formula La _2-x Sr _x NiO _4-Y in which lanthanum is partially substituted by strontium. Another example is cerium nickel oxide of the general formula Ce _2-x Ca _x NiO _4-y in which cerium is partially substituted by calcium. Still other examples include compounds in which the rare earth element is lanthanum and the transition metal is chromium and compounds in which the rare earth element is neodymium and the transition metal is copper. Also included are examples of compounds of the present invention wherein lanthanum (or cerium) is used as the rare earth element, nickel is used as the transition metal and barium is used to partially replace the lanthanum (or cesium).

In the following, barium as a partial substituent for lanthanum in La ₂ CuO ₄ will mainly be described, since Ba-La-Cu-O is the most controversial of all the systems available to date. Some of the compounds of the Ba-La-Cu-O system are described in C. Michel and B. Raveau, Rev. Chim Min. 21 (1984) 407 and C. Michel, L. Er-Rakh. and B. Raveau, Mat, Res. Bu Il., Vol. 20, (1985) 667-671. However, these documents do not disclose superconductivity, and no effort has been made to reveal the superconductivity.

Experiments conducted in accordance with the present invention have shown that compounds in which the rare earth element is partially substituted by one or more other elements of group IIA elements, namely alkaline earth metals, have high temperature Tc super-dryness. Indeed, the Tc of La ₂ CuO _4-y by Sr ²⁺ is higher than that found by Ba ²⁺ and Ca ²⁺ , and its superconductivity-induced diamagnetics are those found by Ba ²⁺ and Ca ²⁺ . Greater than

In fact, only a few oxides are known to exhibit superconductivity, among them DC Johnston. H. Pakash, WH Zachariasen and R. Visvanathan, Mat. Res. Bull. 8 (1973) 777, there is a Li-Ti-O system with a high superconductivity starting point, such as 13.7 ° K. Other known superconducting oxides are described in A. A. Baratoff and G. Binnig, Physics 108 B (1981) 1335, AW Sleight. JL Gillson and FE Bierstedt, Solid State Commun. 17 (1975) 27, including Nb-doped SrTiO ₃ and BaPb _1-x Bi _x O ₃ .

X-ray analysis by Johnston et al. Revealed that there are three different crystal phases (one of which have spinel structures) with high critical temperature theory in Li-Ti-O systems. The Br-La-Cu-O system also exhibits a number of crystal phases, i.e., mixed-atomic copper components having a polarized electron state between non-Jahn-Teller Cu ³⁺ and Jahn-Teller Cu ²⁺ ions. Have

The same applies to systems in which nickel is used instead of copper, where Ni ³⁺ is a Jahn-Teller component and Ni ²⁺ is a non-Jahn-Teller component.

The presence of Jahn-Teller Polaron in deciding the decision is K. H. K. H. Hoeck, H. H. Nickisch and H. By H. Thomas, Helv. Phys. Acta 56 (1983) 237 is theoretically assumed. Flarons have a large attraction between electron-phonons and therefore can easily exhibit superconductivity at high critical temperatures.

ller, Z. Phys. B-Condensed Matter 64(1986) 189-193]에 기록된 바와 같이 다음과 같은 3개의 개개의 결정상을 나타낸다 : -K₂NiF₄구조에 관계하며, 일반식 La_2-xBa_xCuO_4-y(여기에서, x≪1이고 y≥0이다)의 조성을 갖는 층-타입 회티탄석류인 제1상 ; -비-전도성 CuO인 제2상 ; 및 -출발조성이 엄격히 독립적인 것으로 나타나는 일반식 La_1-xBa_xCuO_3-y의 조성을 갖는 거의 입방형 회티탄석인 제3상.Typically, X-ray analysis shows that Ba-La-Cu-O systems are described in JG Bednorz and KA M.

ller, Z. Phys. B-Condensed Matter 64 (1986) 189-193, as shown in the following three individual crystalline phases: -K ₂ NiF ₄ structure, relating to the general formula La _2-x Ba _x CuO _4-y A first phase, which is a layer-type gray titanium pomegranate with a composition of x <1 and y ≧ 0; A second phase which is a non-conductive CuO; And-a third phase which is a substantially cubic gyrite titaniumite having a composition of the general formula La _1-x Ba _x CuO _3-y , in which the starting composition appears to be strictly independent.

Of these three phases, the first phase is shown to be related to high-Tc superconductivity, and the critical temperature is related to the barium concentration in the phase. Clearly, the Ba ²⁺ substitution causes the mixed-atom state of Cu ²⁺ and Cu ³⁺ to maintain a neutral charge. Oxygen deficiency (y) is assumed to be the same for both doped crystallites and undoped sperm.

Both La ₂ CuO ₄ and LaCuO ₃ become metallic conductors at high temperatures in the absence of barium. In reality, both are metals such as LaNiO ₃ . Although they have metallic properties, Ba-La-Cu-O type materials are ceramics like other compounds of RE ₂ TMO ₄ thyme, and their manufacturing methods follow somewhat known ceramic manufacturing principles. For example, a method for preparing Ba-La-Cu-O according to the present invention typically prepares an aqueous solution of each of gilsan strands of barium, lanthanum and copper, coprecipitates them in an appropriate ratio, and adds the coprecipitates to oxalic acid Each forms a sufficient mixture of oxalates, decomposes the precipitate and heats the precipitate to 500-1200 ° C. for 1-8 hours to cause a solid-phase reaction and the resulting product is compressed at a pressure of about 4 Kbar to form pellets. And then reheat to 500-900 ° C. for 30 minutes to 3 hours to sinter the pellets.

In the case of partial replacement of lanthanum with strontium or calcium, it will be apparent to those skilled in the art that certain nitrates thereof are used in place of the barium nitrate of the examples described above. In addition, nitrates thereof are used when copper is to be replaced with another transition metal.

Other precursors of metal oxides, for example carbonates or hydroxides, can be selected according to known principles. It has been found by experiment that the content of the individual compounds in the starting composition plays an important role in the formation of the phase present in the final product. As mentioned above, the final Ba-La-Cu-O system usually obtained contains these three phases, and the second phase is only present in very small amounts, the lanthanum by strontium or calcium (and possibly beryllium) Partial substitution results in only one phase each representing a final La _2-x Sr _x CuO _4-y or La _2-x Ca _x CuO _4-y , where X <0.3.

When each (Ba, La) and Cu content is 1: 1, it can be expected that the three phases are formed in the final product. Although the amount of the second phase, ie the CuO phase, can be neglected, the relative capacity of the other two phases depends on the content of barium in the La _2-x Ba _x CuO _4-y complex. In the case of a 1: 1 ratio and x = 0.02, the onset of the positional transition was observed, i.e. the resistance increased with decreasing temperature, and no superconductivity appeared.

For x = 0.1 at the same 1: 1 ratio, a resistance drop occurs at a very high critical temperature of 35 ° K.

When the ratio of (BA, La) to Cu in the starting composition is 2: 1, the composition of the La _2x CuO ₄ : Ba phase, which is assumed to be related to superconductivity, results from the absence of the CuO phase and only two phases. . When the barium content is x = 0.15, a resistive drop occurs at Tc = 26 ° K, respectively.

In the method for preparing the Ba-La-Cu-O complex, two times of heat treatment are performed at elevated temperature for precipitation for several hours. When experiments were carried out according to the invention it was found that the best results were obtained when they were decomposed at 900 ° C., reacted for 5 hours and sintered again at 900 ° C. for 1 hour.

In the case of a 2: 1 composition, rather high temperatures are allowed because the melting point of the composition is higher in the absence of excess copper oxide. However, it is not possible to obtain one-phase compounds by high temperature treatment.

The measurement of dc conductivity is performed between 300 and 4.2 ° K. In the case of barium-doped samples with x <0.3 at a current density of 0.5 A / cm ² , high temperature metallization is found with an increase in resistance at low temperatures. At still lower temperatures, a sharp drop in resistance (> 90%) occurs, which is partially suppressed for higher charge densities. This characteristic drop phenomenon is considered as a function of annealing conditions, ie temperature and oxygen partial pressure. For example, for samples annealed in air, the transition from initiator action to localized action has not been found to be very obvious, but annealing under a slight depressurization atmosphere results in increased resistance and a more pronounced ubiquitous effect. Cause. At the same time, the starting point of the resistance drop is moved toward a higher threshold temperature. However, longer annealing times completely destroy the superconductivity.

The dc conductivities of representative Ba-La-Cu-O compositions are measured to determine their low temperature action and they observe high Tc. This measurement is performed using the well-known four-point probe technique shown in FIG. Rectangular samples 10 of Ba _x , La _5-x , Cu ₅ O _{5 (3-y)} are cut from the sintered pellets and placed in gold-deposited electrodes 12A and 12B about 0.5 microns thick. . Indium wires 14A and 14B are in contact with electrodes 12A and 12B, respectively. The sample is placed in a continuous flow chiller (Leybold-Hereaus) 16 and measured at a temperature range of 300 to 412 ° K.

Electrodes 12A and 12B are connected to a circuit comprising a power source 18 and a variable resistor 20. Indium conductors 22A and 22B are pressed into contact with sample 10 and fixed with silver paint 24. The wires 22A and 22B are connected to the voltage reading system 26. By accurately measuring the current and voltage, the resistance of the sample 10 can be known. As the form used for such measurements, a computer is provided that provides a computer-controlled fully automatic system for temperature changes, data acquisition and processing.

In FIG. 2 the low temperature dependence of the resistance (ρ, Ω-cm units) in the composition Ba _x La _5-x Cu ₅ O _{5 (3-y)} is shown for two different values of x. For the upper two curves, the value of x (Ba) is 1 and uses the left vertical scale. For the lower curve, the value of x is 0.75 and the right resistance scale is used. Data were taken for current densities of different values: for the top curve and 0.25A / cm ² is 0.50A / cm ² for the middle and lower curves.

For barium-doped samples with X (Ba) <1.0, for example x <0.3, the high temperature metallic action with increasing resistance at low temperatures can be seen as shown in FIG. . At lower temperatures, a sharp drop in resistance (Figure 2 upper curve, left scale) occurs, which is partially suppressed for high current densities. This characteristic drop is considered as a function of the annealing conditions, ie the temperature and oxygen partial pressure shown in FIG. For samples annealed in air, the transition from biasing to localization was not found to be very obvious, as indicated by the minimum resistance in the 80 ° K range. However, slightly reduced annealing in the atmosphere leads to increased resistance and more pronounced local effects. At the same time, the starting point of the resistance drop moves toward the 30 ° K part. Curves 4 and 5 (FIG. 3) recorded for samples treated at 900 ° C. show the occurrence of shoulders at lower temperatures, more pronounced in curve 6. At the annealing temperature of 1040 ° C., the high conducting phase almost disappears. Long annealing times and / or high temperatures typically destroy superconductivity.

The mixed-atomic state of copper is important for electron-phonon bonds. Therefore, the concentration of electrons is changed by the Ba / La ratio. Representative curves for samples with lower Ba concentrations of 0.75 are shown in FIG. 2 (right scale). Its resistance is reduced by more than three times, demonstrating that the main part starts at around 35 ° K and has superconductivity below 13 ° K, as shown on the extended temperature scale of FIG. Figure 4 also shows the effect of typical current densities on granular compounds. Current densities of 7.5, 2.5 and 0.5 A / cm ² are passed through the superconducting composition.

Upon cooling the sample from room temperature, the resistance data first shows a metal-type decrease. The change from low temperature to increase occurs for Ca compounds and for Ba-substituted samples. This increase is accompanied by a drop in resistance and shows the initiation of superconductivity at 22 ± 2 ° K and 33 ± 2 ° K for Ca and Ba compounds, respectively. For the Sr compound, the resistivity remains a metal-type decrease with respect to the resistive drop at 40 ± 1 ° K. However, the presence of local effects depends a lot on the alkaline-earth ion concentration and the method of preparing the sample, ie the annealing conditions, and also on the ultimate concentration. All samples with low concentrations of Ca, Sr and Ba show a strong tendency of localization before resistance drops occur.

Clearly, the starting point of superconductivity, i.e. the critical temperature value Tc, depends on the oxygen content of the final compound, among other factors. Specific oxygen deficiency seems to be essential for the material to have a high Tc action. According to the present invention, the above-described method for making La ₂ CuO ₄ : Ba complex can be supplemented by an annealing step during which the oxygen content of the final product can be controlled. Of course, what is mentioned in connection with the production of La ₂ CuO ₄ : Ba compounds applies equally to other compounds of the general formula RE ₂ TMO ₄ : AE (eg Nd ₂ NiO ₄ : Sr).

When the heat treatment for decomposition and reaction and / or sintering is carried out at relatively low temperatures, ie below 950 ° C., the final product is annealed at about 900 ° C. for about 1 hour under reduced pressure atmosphere. It is assumed that the net effect of this annealing step is to remove oxygen atoms from specific positions in the matrix of the RE ₂ TMO ₄ complex to cause distortion in its crystalline structure. In this case the O ₂ partial pressure for annealing will range from 10 ⁻¹ to 10 ⁻⁵ bars.

When using relatively high temperatures for heat treatment, the annealing step is advantageously carried out in a slightly oxidizing atmosphere. This is to compensate for the estimated excessive removal of oxygen atoms from the system by high temperature or causing too much distortion of the crystalline structure of the system.

As a function of temperature, the resistivity and susceptibility measurements of Sr ²⁺ and Ca ²⁺ -doped La ₂ CuO _4-y ceramics show the same general trend as Ba ²⁺ -doped samples: resistance drop ρ ( T), and crossover for diamagnetics at slightly lower temperatures. Substantially Sr ²⁺ containing samples get a higher starting point than Ba ²⁺ and Ca ²⁺ containing samples. Moreover, the diamagnetic mass ratio is about three times larger than that for Ba samples. Since the ion radius of Sr ²⁺ closely matches that of La ³⁺ , the size effect does not seem to cause superconductivity. Conversely, this may be the opposite case as the data for Ba ²⁺ and Ca ²⁺ show.

The highest Tc 'for each of the dopant ions to be irradiated occurs for their concentration at room temperature, with the RE _2-x TM _x O _4-y structure being substantially electron-phonon interaction enhanced by substitution. It is closely related to the tetragonal to tetragonal structural transitions associated with the action. Alkaline earth substitution of rare earth metals is very important and seems to virtually produce TM ions without the e _g Jahn-Teller trajectory. Thus, such J.-T. Orbit, i.e. J.-T. The absence of holes probably plays an important role in Tc enhancement. Examples of the present invention are given using different transition metal elements in superconducting compositions, while copper oxide compositions with mixed valences exhibit unique and particularly important properties, having superconducting properties at temperatures above 26 ° K. These mixed valence copper compositions may contain rare earth elements, and / or rare earth elements that may be substituted with alkaline earth elements. The amount of oxygen in these compositions can vary depending on the method of preparation and is an amount that meets the valence requirements of the composition. Compositions based on these coppers often have a layer-like structure in the form of gray titanium. For a more detailed description of some of the crystal structure types that may occur, reference is made to Michel and Raveau in Rev. Chim. Min. 21, 407 (1984) and in C. Michel et al, Mat. Res. Bull., Vol. 20, 667-671 (1985).

While the present invention describes certain embodiments of the composition, it will be apparent to those skilled in the art that changes may be made without departing from the spirit and scope of the invention. For example, the compositions within the scope of the present invention contain rare earth elements and transition metal elements, but the ratio of these elements because the crystalline structure can adjust the valences of these elements and also maintain a layer-like structural phase exhibiting superconductivity Can change.

In addition, the oxygen content (i.e., oxygen deficiency or excess) in these compositions in stoichiometric or non-stoichiometric amounts can be reduced or doped to rare earth and transition metal sites in the crystal structure while producing compounds. It can be changed by using different amounts. Many of the forms that can be distorted and encompassed by this type of crystalline structure are readily apparent by reference to the aforementioned Michael and Raveau publications. Accordingly, the present invention relates broadly to mixed (doped) transition metal oxides having a layer-like structure exhibiting superconducting action at temperatures above 26 ° K. Among these materials, mixed copper oxides having a polyatomic state provide high Tc and desirable superconducting properties.

Claims (6)

The rare earth element (RE) is partially substituted by one or more elements of the alkaline earth group (AE), and the oxygen content is distorted in the resulting crystal structure. General formula RE _2-x AE _x TMO _4-y , where TM represents a transition metal and has a transition temperature of at least 26 ° K adjusted to an amount to include a phase having a composition of X <0.3 and y <0.5. Superconducting compound in the form of RE ₂ TMO ₄ . The compound of claim 1, wherein the rare earth element (RE) is lanthanum and the transition metal (TM) is copper. The compound of claim 1 wherein barium is used as a partial substituent for the rare earth element and X <0.3 and 0.1 ≦ y ≦ 0.5. The compound of claim 1 wherein calcium is used as a partial substituent for rare earth elements and x <0.3 and 0.1 ≦ y ≦ 0.5. 2. A compound according to claim 1 wherein strontium is used as a partial substituent to the rare earth element and x <0.3 and 0.1 ≦ y ≦ 0.5. Preparing an aqueous solution of rare earth and transition metal nitrates, and one or more alkaline earth metals and coprecipitation them in an appropriate proportion; Co-precipitate is added to oxalic acid to form an intimate mixture of each oxalate; Destroying the precipitate and causing the solid-phase reaction by heating the precipitate to a temperature of 500 to 1200 ° C. for 1 to 8 hours; Cooling the resulting powder product; The powder is pressed at a pressure of 2-10 Kbar to form pellets; Readjust the temperature to 500-1000 ° C. for 30 minutes to 3 hours to dissipate the pellets; The pellet was placed in a protected atmosphere to adjust the oxygen content of the final product having a final composition in the form of RE _2-x TMO _4-y (where x <0.3 and 0.1 <y <0.5). Superconducting compounds of the form RE ₂ TMO ₄ (where RE is a rare earth element and TM is a transition metal), characterized by further annealing for 30 minutes to 5 hours at How to prepare.

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