CA1341621C - Superconductivity in an oxide compound system without rare earth - Google Patents

Abstract

Described is a superconducting composition comprising a metal oxide of the formula T d M* e Cu f O g wherein "T" is a trivalent transition metal such as Bi, Tl, In, Sb, or mixtures thereof; "M*" is a mixture of alkaline earth metals such as Sr and Ca, Sr and Mg, and Ca and Mg in ratio of the alkaline earth metal of larger atomic radius (M L) to the alkaline earth metal of smaller atomic radius (M S) of from about 1:1 to about 3:1; "d" is a number from about 1 to about 3; "e" is a number from about 1 to about 6; "f" is a number from about 1 to about 6; "g" is a number between from about (3d + 2e + 2f)/2 to about (3d + 2e + 3f)/2 that provides the metal oxide with zero electrical resistance at a temperature of 77°K or higher. Preferably "T" is bismuth; "M*" is Ca and Sr at ratio of 1:2; "d" is 2; "e" is 3; "f" is 2 and "g" is a number between about 8 to about 9 which provides said composition with zero electrical resistance at a temperature of 77°K or higher.

Description

APPLICATION FOR PATENT
Inventor: CHING-WU CHU

Title: SUPERCONDUCTIVITY IN AN OXIDE
COMPOUND SYSTEM WITHOUT RARE EARTH
Background of the Invention This invention relates to superconducting compositions, i.e., compositions offering no electrical resistance at a temperature below a critical temperature;
to processes for their production and to methods for their use.
Superconductivity was discovered in 1911.
Historically, the first observed and most distinctive property of a superconductive material is the near total loss of electrical resistance by the material when at or below a critical temperature that is a characteristic of the material. This critical temperature is referred to as the superconducting transition temperature of the material, Tc.
The history of research into the superconductivity of specific materials began with the discovery in 1911 that mercury superconducts at a transition temperature of about 4 K. In the late 1920's, NbC was found to superconduct at a higher temperature, namely up to about 10.5 K.
Thereafter other compounds and alloys of Nb were examined and various Nb compositions were discovered with progressively, but only slightly higher, superconducting transition temperatures. In the early 1940's NbN was observed with a transition temperature of about 14 K;
Nb3Sn was reported in the early 1950's; Nb3(Al-Ge) was reported in the late 1960's; and Nb3Ge was reported in the early 1970's to have a transition temperature of up to 21 K. Careful optimization of Nb3Ge thin films led to an increase of the critical temperature for such material up to 23.3 K. While this work led to progress the maximum temperature at which superconductivity could occur was raised to only 23.3 K since research started three-quarters of a century ago. The existing theories explained the superconductivity of these materials, but did not predict superconductivity of higher than 40 K.
Significant progress in finding materials which superconduct at higher transition temperatures than that of Nb3Ge thin films was not made until 1986.
In 1986, specially prepared coprecipitated and heat treated mixtures of lanthanum, barium, copper and oxygen, that have an abrupt decrease in resistivity "reminiscent of the onset of percolative superconductivity" were reported by J.G. Bednorz and R.A. Muller, "Possible High Tc Superconductivity In The Ba-La-Cu-O System,"
Z.Phys.B.-Condensed Matter, 64, pp. 189-193 (1986). Under atmospheric pressure conditions, the abrupt change in resistivity for these compositions -- i.e., that temperature at which a portion of the material begins to show properties reminiscent of percolative superconductivity -- were reported to approach the 30 K range. The authors refer to this phenomenon as a "possible" case of superconductivity. The compositions reported by Bednorz et al to have such properties at a temperature as high as 30 K
comprise La5_xBaxCu5O5(3_Y) where X = 0.75 to 1 and Y > 0.
Superconductivity is a potentially very useful phenomenon. It reduces heat losses to zero in electrical power transmission, magnets, leviated monorail trains and many other modern devices. However, superconductivity of a material occurs only at very low temperatures. Originally, and until the inventions outlined herein, liquid helium was the required coolant to provide the conditions necessary for superconductivity to occur.
It would be desirable to produce a superconducting composition that has a transition temperature which exceeds those of superconducting compositions previously described.
It would be particularly desirable to develop a superconducting composition that has a TC of 77 K or higher. Such a composition would enable the use of liquid nitrogen instead of liquid helium to cool the superconducting equipment and would dramatically decrease the cost of operating and insulating superconducting equipment and material.
The prior art teaches a mixed phase oxide prepared according to a nominal formulation of Y1.2Bao.8Cu0Y ( "y" is a number from 2 to 4) that superconducts at a temperature of 80 K or greater. The mixed phase oxide can comprise a green and black phase with the black phase being the phase responsible for the high temperature (i.e., TC = 77 K or greater) superconduction and being of the formula YBa2Cu3O6+a (a is a number between 0.1 to 1.0).

A high temperature superconducting composition of the general formula LM2A30 6+a may be prepared wherein "L" is scandium, yttrium, a rare earth element (atomic numbers 51 to 71) or mixtures thereof; "M" is barium, strontium, calcium, magnesium, mercury or mixtures thereof; "A" is copper, bismuth, titanium, tungsten, zirconium, tantalum, niobium, vanadium or mixtures thereof; and "M" is preferably barium or strontium and "A" is preferably copper.
Confirmation by other workers in the field of species LBa2Cu3O6+a as a high temperature superconductive composition has been widespread since disclosure of the high temperature superconducting mixed phase oxide prepared to the nominal formula Y,.2Bao.8CuOY.
The objective of a superconducting composition having TC of 77 K or higher has been achieved with the LM2A3O6+a compositions as mentioned above. It is, however, still desirable to develop other compositions which do not require the presence of a rare earth element and which will superconduct at a temperature of 77 K or higher. The prior art acknowledges the possibility of such materials in the context of the general formula [L1_XMx]aAbOY wherein the value of "x" may be 1.0 maximum, in which case the rare earth element "L" is removed and the general formula becomes MaAb0Y.
Michel et al has recently described the observance of superconductivity in a Bi2Sr2Cu2O7 composition up to a TC of 22 K. The TC of such composition was reported to be highly sensitive to impurities. Additionally, a brief news report of an observation of superconductivity in a Bi-Sr-Ca-Cu-O system between 75 and 120 K recently appeared in Japan Economic News on January 22, 1988, but no details were given concerning the composition, processing or structure of the material.

Summary of the Invention In accordance with one aspect of the invention there is provided a material which is superconductive at a temperature of 77 K or higher, said material comprising a multiphase oxide of nominal composition M*aA*bOy wherein M*
is a mixture of divalent alkaline earth metals selected from the group consisting of Ba, Sr, Ca and Mg wherein the ratio of the alkaline earth metal of larger atomic radius to the alkaline earth metal of smaller atomic radius is from about 1:1 to about 3:1; A* is a mixture of Cu and a trivalent metal selected from the group consisting of Bi and Ti wherein the molar ratio of Cu to said trivalent metal is from about 1:1 to about 3:1; "a" is 1 to 2; "b" is 1; and "y" is 2 to 4.
In accordance with another aspect of the invention there is provided a material which is superconductive at a temperature of 77 K or higher, said material comprising a multiphase oxide of nominal composition BiCaSrCuO2y wherein "y" is 2 to 4 and having a sufficient quantity of a crystalline phase composition of a formula Bi2CaSr2Cu2Og wherein "g" is a value from about 8 to about 9 which provides said crystalline phase composition with zero electrical resistance at a temperature of 77 K or higher to cause the material to exhibit zero electrical resistance at a temperature of 77 K or higher.
In accordance with yet another aspect of the invention there is provided an oxide composition of nominal formula TdM*eCufOg wherein "T" is Bi or TI; "M*" is a mixture of divalent alkaline earth metals selected from the group consisting of Ba, Sr, Ca and Mg wherein the ratio of the alkaline earth metal of larger atomic radius to the alkaline earth metal of smaller atomic radius is from about 1 to about 3; "d" is a number from about 1 to about 3; "e" is a number from about 1 to about 6; "f" is a number from about 1 to about 6; and "g" is a number from about 0.5 (3d + 2e +
2f) to about 0.5 (3d + 2e + 3f) that provides the oxide composition with zero electrical resistance at a temperature of 77 K or higher.
In accordance with yet another aspect of the invention there is provided a crystalline phase composition comprising 134 1 6[1 -5a-cations of Bi, Ca, Sr, and Cu approximating the ratio of 2:1:2:2 for Bi:Ca:Sr:Cu and which exhibits zero electrical resistance at a temperature of 77 K or higher.
In accordance with yet another aspect of the invention there is provided a superconducting oxide composition of nominal formula TaM*eCufO9 wherein "T" is Bi or TI ; "M*" is a mixture of divalent alkaline earth metals selected from the group consisting of Ba, Sr, Ca and Mg wherein the ratio of the alkaline earth metal of larger atomic radius (M') to the alkaline earth metal of smaller atomic radius (MS) is from about 1 to about 3; "d" is a number from about 1 to about 3;
"e" is a number from about 1 to abut 6; "f" is a number from about 1 to about 6; and "g" is a number from about 0.5 (3d + 2e + 2f) to about 0.5 (3d + 2e + 3f) that provides the oxide composition with zero electrical resistance at a temperature of 77 K or higher, wherein said composition is made by a process comprising the steps of: compressing a mixture of solid powdered compounds comprising: (a) T203, (b) MLCO3 or MLO, (c) M8C03 or MSO, and (d) CuO in proportions appropriate to yield said formula; heating the compressed powder mixture to a temperature of from about 800 C to about 910 C fro a time sufficient to complete the solid state reaction; and quenching said reacted compressed mixture to room temperature.
More specifically, an embodiment of the present invention describes a superconducting composition comprising a metal oxide of the formula TaM*eCufOg wherein "T" is a trivalent transition metal such as Bi, Tl, In, Sb, or mixtures thereof; "M*" is a mixture of alkaline earth metals such as Sr and Ca, Sr and Mg, and Ca and Mg in ratio of the alkaline earth metal of larger atomic radius (ML) to the alkaline earth metal of smaller atomic radius (MS) of from about 1:1 to about 3:1; "d" is a number from about 1 to about 3; "e" is a number from about 1 to about 6; "f" is a number from about 1 to about 6; "g" is a number between from about (3d + 2e + 2f)/2 to about (3d + 2e + 3f)/2 that provides the metal oxide with zero electrical resistance at a temperature of 77 K or higher. Preferably "T" is bismuth;
"M*" is Ca and Sr at a ratio of 1:2; "d" is 2; "e" is 3; "f"
is 2 and "g" is a number between about 8 to about 9.
The trivalent element "T" and the selection of an alkaline earth metal pair in appropriate ratio in view of -5b-their atomic radius to correspond the alkaline earth metal pair to the atomic radius size of the trivalent element "T"
employed, is crucial to obtaining a metal oxide composition that will crystallize to a form favorable to high temperature superconduction. A crystalline form in which Cu-atoms are in planar configuration is required for high Tc. The crystalline form that provides for high T, is a perovskite related structure with substantial deviations from the ideal perovskite arrangement of metal atoms. Hence in the high Tc species of Bi2Ca1Sr2Cu2Og (g = 8 to 9) bismuth appears to be concentrated in layers similar to the Bi2O2 slabs of phases such as BaBi4Ti4O15 discussed by B.
Aurivailius, Arkiv Kemi 1, 499 (1950). For the species Bi2CaSr2Cu2Og (g = 8 to 9) the weak electron density associated with every fourth layer of the crystalline structure suggests interlayers region of weak bonding. In the new structure that provides Tc > 77 K, copper-oxygen layers appear to be continuous over hundreds of unit cells.

Brief Description of the Drawings Fig. 1 illustrates DTA, TGA, and DTG results for BCSCO-a and -b in air with compositions Bi:Ca:Sr:Cu being 1:1:1:1 and 1:1:1:2. The scan speed for temperature is 20 /min. TM is the meling point.
Fig. 2 illustrates the temperature dependence of resistance for Bi-Ca-Sr-Cu oxide superconductor compositions prepared of nominal formula 1:1:1:1 (BCSCO-a); 1:1:1:2 (BCSCO-b); and 1:1:1:3 (BCSCO-c).
Fig. 3 illustrates the temperature dependence of magnetization for the Bi-Ca-Sr-Cu oxide superconductor species BCSCO-a and BCSCO-c.
Fig. 4 illustrates selected-area electron diffraction pattern of the Bi-Ca-Sr-Cu oxide superconductor showing hk0 diffraction spots. Strong spots correspond to 2.7 x 2.7 A subcell, while superlattice reflections along a' and b' indicate spacings of 5.4 and 27.2 A
respectively.
Fig. 5 illustrates selected-area electron diffraction pattern of the 002 diffraction row, which is streaked but show's a strong 15.4 A periodicity. The 004 difraction is indicated. Also illustrated is a high-resolution image taken parallel to the layers shows the 15.4 A spacing, with subspacings of 3.8 A. The contrast of these layers differs, suggesting a possible ABAC-ABAC type stacking of perovskite units. A structural defect (arrowed) may correspond to a Bi-free region of Ca-Sr-Cu perovskite.
Fig. 6 illustrates the selected-area OkQ electron diffraction pattern as characterized by an A-centered 27 x 31 A lattice. Also illustrated is a high-resolution image of the (100) plane revealing numerous stacking faults and defects as well as the A-centered layered structure. Though most of the structure appears to be orthogonal, locally inclined blocks may indicate a fine-scale twinning or may represent "monoclinic" regions of related but different structure.
Fig. 7 illustrates X-ray results for BCSCO-b synthesized at different temperatures: a - 820 C, b - 864 C, c - 880 C, d - the superconducting phase. Curve e is for BCSCO-c with composition ratio of 1:22:14:6.2 synthesized at 850 C.
Fig. 8 illustrates resistance (R) vs. temperature (T) for BCSCO-b synthesized at different temperatures:
a - 820 C, b - 864 C, c - 880 C. Curve d is for BCSCO-c.
Fig. 9 illustrates magnetization (M) vs. T for BCSCO-b synthesized at different temperatures: a - 820 C, b - 864 C, c - 880 C. Curve d is for BCSCO-c.
Fig. 10 illustrates R - T for BCSCO-b in different magnetic fields.

Detailed Description of the Preferred Embodiments It is known to make superconducting compositions of the formula [L1-XMX]aAbOY wherein "L" is scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holminum, erbium, thulium, ytterbium, or lutetium, and preferably "L" is yttrium, lanthanum, neodynium, samarium, europium, gadolinium, erbium or lutetium; "A" is copper, bismuth, titanium, tungsten, zirconium, tantalum, niobium, vanadium or mixtures thereof and "A" preferably is copper; "M" is barium, strontium, calcium, magnesium, mercury or mixtures thereof and "M" is preferably barium or strontium; and "a"
is 1 to 2; "b" is 1; and "y" is about 2 to about 4; "x" is 0.01 to 1.0 maximum and "x" is preferably from about 0.60 to about 0.90 and most preferably from about 0.65 to about 0.80 and when "a" is 2 "x" is preferably from about 0.01 to about 0.5 and most preferably from about 0.07 to about 0.5.

Production of an oxide complex of Y-Ba-Cu-O wherein x = 0.4 and a = 2 produced a multiphase oxide material of nominal formula Y1.2Bao.8CuOy which exhibited zero electrical resistance at a temperature of 77 K or greater.
The phase within that material determined to be the crystalline phase composition responsible for such high temperature superconduction was isolated and identified to be YBa2Cu3O6+8; wherein 8 is a value between 0.1 to 1.0 that provides the crystalline phase composition with zero electrical resistance at a temperature of 77 K or higher.
Accordingly, a new class of compostions of formula LM2A3O6+0; preferably LM2Cu3O6+8; was disclosed which had zero electrical resistance at a temperature of 77 K or higher.
Another species of materials within the formula [L1-xMx]aAb0y has been found which has zero electrical resistance at a temperature of 77 K or higher. The species comprises that class of compositions wherein "x"
equals 1, to yield a formula of M*aA*bOy wherein the M* constituent comprises a mixture of divalent alkaline earth metals and the A* constituent comprises a mixture of copper with at least one other "A", preferably bismuth. In a preferred composition the M* constituent is a 1:1 mixture of Ca and Sr, the A* constituent is a 1:1 mixture of Cu and Bi and "a" is 1. Accordingly, an oxide material prepared to a nominal formula of (Cao=sSro=5)1(Cuo=sBio=5)iOy yields a multiphase material which exhibits zero electrical resistance at a temperature of 77 K or higher. The material does not contain a rare earth metal. In this regard it is believed that bismuth, a trivalent element, serves a similar function to that of a trivalent rare earth with regards to creating a perovskite related crystalline form favorable to the occurrance of high temperature (i.e., Tc >_77 K) superconduction. Hence, for convenience the nominal formulation may be rewritten as follows:

Bi1CaiSrlCu1O2y (1:1:1:1) It has been found that the production of such high temperature superconducting material may be facilitated by employing copper in an excess up to about six times the amount required to produce a material of the 1:1:1:1 nominal formulation described above. A material produced to a nominal composition of:
BilCalSriCu3Oh (1:1:1:3) wherein "h" is a number between 6.5 to 8.0, is a multiphase material which exhibits zero electrical resistance at 77 K
or higher. In the sense of the ratio of trivalent constituent to alkaline earth constituent to copper, the 1:1:1:3 nominal composition is analogous to the LMCu3O6+a class of high temperature superconductor materials.
As before noted, whether prepared as a 1:1:1:1 or a 1:1:1:3 nominal composition, or even as a (1:1:1:2) Bi1Ca1Sr1Cu2O,, where "j" is between 5.5 and 6.5, each high temperature superconducting material comprises a multiphase oxide.
Examination of the multiphase oxide material reveals at least four distinct phase compositions. The nominal composition of that phase determined to be the phase responsible for the high temperature superconduction has been determined to be as follows:
Bi2Ca1Sr2Cu2O8+a (2:1:2:2) where a is a value between 0.1 to 1.0 that provides the phase composition with zero electrical resistance at a temperature of 77 K or higher.
Trivalent metals ("T") other than bismuth may be employed in the production of a high temperature superconductive oxide material of the formula M*aA*bOY.
Desirably such other trivalent metals should have an atomic radius no smaller than 1.5 A and no larger than 2.1 A.

The trivalent element "T" and the selection of an alkaline earth metal pair in appropriate ratio in view of their atomic radius to correspond the alkaline earth metal pair to the atomic radius size of the trivalent element "T" employed, is crucial to obtaining a metal oxide composition in which a phase will crystallize to a form favorable to high temperature superconduction. A
crystalline form in which Cu-atoms are in planar configuration is required for high Tc. The crystalline form that provides for high Tc is a perovskite related structure with substantial deviations from the ideal perovskite arrangement of metal atoms. Hence in the high Tc bismuth species, bismuth appears to be concentrated in layers similar to the Bi2O2 slabs of phases such as BaBi4Ti4O15 discussed by B. Aurivilius, Arkiv Kemi 1, 499 (1950). For the species Bi2CaSr2Cu2Og (g = 8 to 9) the weak electron density associated with every fourth layer of the crystalline structure suggests interlayers region of weak bonding. High resolution transmission electron microscopy (TEM) images show that the compound has a four-layer structure and that the bonding between every fourth layer is weak. In the new structure that provides a Tc of 77 K or greater, copper-oxygen layers appear to be continuous over hundreds of unit cells.
For convenience the phase composition within a multiphase material prepared with a nominal composition Bi:Ca:Sr:Cu of 1:1:1:1; 1:1:1:2; or 1:1:1:3 may be represented as a metal oxide of the formula TdM*eCuf0g wherein "T" is a trivalent transition metal such as Bi, Al, Ba, T1, In, Sb, or mixtures thereof; "M*" is a mixture of alkaline earth metals such as Sr and Ca, Ba and Sr, Ba and Ca, Sr and Mg, and Ca and Mg in a ratio of the alkaline earth metal of larger atomic radius (ML) to the alkaline earth metal of smaller atomic radius (Ms) of from about 1:1 to about 1:3; "d" is a number from about 1 to about 3; "e" is a number from about 1 to about 6; "f" is a -11- 134 1 621 number from about 1 to about 6; "g" is a number between from about (3d + 2e + 2f)/2 to about (3d + 2e + 3f)/2 that provides the metal oxide with zero electrical resistance at a temperature of 77 K or higher. Preferably "T" is bismuth; "M*" is Ca and Sr at ratio of 1:2; "d" is 2; "e"
is 3; "f" is 2 and "g" is a number between about 8 to about 9.
A method for making such TdM*eCuf0g containing superconductive composition oxide materials, includes the following steps, and for convenience is referred to as the compressed powder reaction method. Selected amounts of solid powdered compounds containing T, ML, Ms, A, and 0 are thoroughly mixed preferably by selecting appropriate amounts of T203, MLCO3, MsCO3 (or MLO and MSO)and AO. The thoroughly mixed powder mixture is compressed into pellets which are thereafter reacted at a temperature between about 800 C and about 910 C, preferably about 850 C to about 890 C, for a time sufficient to complete the solid state reaction. Thereafter the reacted pellets are rapidly quenched to room temperature. Mixing is preferably accomplished by an intensive mixer such as a jar mill or more preferably a ball mill. Pelletization of the oxide mixture is carried out at an applied pressure of from about 100 to about 30,000 psi and preferably at an applied pressure of from about 100 to about 500 psi, most preferably at about 500 psi. Reaction of the pelletized mixture may be conducted in air for about 5 minutes to about 24 hours, and most preferably in a reduced oxygen atmosphere of about 2000 p for about 5 to about 30 minutes preferably for about 5 to about 15 minutes. Following the completion of the reaction step the reacted pellet composition is rapidly quenched to room temperature in air.
Sample preparation parameters can affect the electronic and magnetic properties of the TdM*eCufOg class of oxide compounds drastically. It has been observed that the formation conditions for TdM*eCufOg for different "T's" are different. The reaction time, the reaction temperature, the quenching rate, the reaction atmosphere and the compositions are all inter-related. For instance, oxide complexes within this class can be made insulating, partially superconducting or completely superconducting by varying the reaction temperature and the quenching rate while keeping the compositions unchanged. The reaction temperature can be reduced by increasing the "d"
parameter, reducing the "f" parameter, increasing the "T"
component with greater atomic radius or doping the composition with monovalent alkaline elements.
Generally wherein the reaction atmosphere is a reduced oxygen atmosphere of about 2000 p the reaction may be conducted at a lower temperature than where the reaction is carried out under atmospheric conditions.
Under a reduced oxygen atmosphere of about 2000 p the reaction temperature required to produce an oxide complex having superconducting properties is from about 800 to about 950 C and preferably from about 820 to about 910 C.
For a reaction under atmospheric conditions the temperature required to produce superconducting properties is from about 800 C to about 910 C preferably from about 850 C to about 890 C. For either type of reaction atmosphere higher temperatures, up to the melting point of the lowest melting component of the starting materials in eutectic admixture, could be employed; however it is sometimes preferred to use such higher reaction temperatures since they may tend to promote the formation of the oxide complex compared to that optimum attainable by use of lower reaction temperatures. The optimum reaction temperature is dependent upon the elemental composition of the oxide complex being prepared and the optimum reaction temperature for a particular oxide complex may be established without undue experimentation.
Reactions carried out at temperatures significantly lower than as discussed above generally result in an oxide complex that has only insulating or semiconducting electrical properties rather than superconducting properties.
The reaction atmosphere employed also influences the time of reaction to completion. Generally, reaction under a reduced oxygen atmosphere of about 2000 p requires a significantly shorter reaction, on the order of about 3 to 45 minutes for gram size reactions, compared to an atmospheric reaction, which generally requires from about 5 minutes to 8 hours for gram size reactions. A similar trend would be expected for larger scale reactions, although the optimum reaction time for such larger scale reaction would have to be determined by observation. One method for determination of the completion of reaction is to monitor samples by X-ray diffraction for depletion of diffraction peaks that correspond to the starting material and growth to maximum intensity of diffraction peaks which correspond to the desired TdM*eCuf09 phase. The optimum reaction time is dependant upon the elemental composition of the oxide complex being prepared and the reaction temperature and may be established by observation without undue experimentation. Optimum superconducting properties are obtained by timing the reaction to that point wherein the maximum amount of starting materials have been converted to the desired TdM*eCufO9 phase.
When the reaction has proceeded to the point of maximum attainable TdM*eCuf09 phase content, it is desirable to then rapidly quench the reaction material to room temperature. This generally produces a narrower temperature transition range between Tco and Tc for the i oxide complex so produced and also terminates any side reaction that may occur which would otherwise convert the TdM*eCuf09 phase content to an inferior superconducting phase structure. For material produced under atmospheric conditions rapid quenching is conveniently obtained by immediately transferring the reacted material from the heated reaction vessel to a heat sink. For gram quantities of material an aluminum plate adequately functions as a suitable heat sink for rapid quenching.
Wherein the reacted material has been prepared in a reduced oxygen atmosphere, upon completion of the reaction the sample may be rapidly quenched by passing oxygen at ambient temperature over the reacted sample.
The superconducting compositions of the present invention have the potential for being used in a wide variety of applications. For example, when used in a wire or conductor form, they may be used in electrical power transmission, energy storage, controlled fusion reaction, electricity generation, mass transportation and magnets.
In a thin film form, they may be used in ultra-sensitive detectors and in ultra-fast computers. In addition, they may be used in a superconducting-magnetic-superconducting multi-layer form for use in ultra-sensitive ultra-fast-electromagnetic micro devices.
The following discussion of Bi-Ca-Sr-Cu-oxide systems is representative of the TdM*eCuf09 oxide complexes and methods of producing the oxide complexes of the invention.
Generally, the standard 4-probe technique was used to measure resistivity, and an inductance bridge was employed for ac magnetic susceptibility X-determination and a magentometer was used for dc magnetization measurements.
The temperature was measured using the Au+0.07%Fe-chromel, and chromel-alumel thermocouples in the absence of a magnetic field, and a carbon-glass thermometer in the presence of a field. The latter was calibrated against the former without a field. Magnetic fields up to 6T were generated by a superconducting magnet.
Three Bi-Ca-Sr-Cu-O (hereafter BCSCO) samples were synthesized by the described solid-state reaction techniques from appropriate amounts of Bi2O3i CuO, SrCO3, and CaCO3. The BCSCO samples were prepared according to a nominal composition of 1:1:1:1 for BCSCO-a; 1:1:1:2 for BCSCO-b, and 1:1:1:3 for BCSCO-c. The starting ingredients used were Bi2O3, (99-99.999%), Bi(NO3)3.5H2O
(99.99%), CaCO3 (99-99.995%), SrCO3 (99-99.999%) and CuO

(99-99.999%). The initial powder materials of appropriate amounts were thoroughly mixed. The mixture was then heated and cooled in air. The heat treatment conditions were different for samples BCSCO-a and -b. The DTA, TGA, and DTG results are shown in Fig. 1 for BCSCO-a and -b, with compositions of Bi:Ca:Sr:Cu = 1:1:1:1 and 1:1:1:2, respectively. Three reaction peaks at T1, T2, and T3 are are clearly evident below melting. This observation is typical for all compositions examined, provided that the Sr/Ca ratio is greater than 0.7. The increase of Cu tends to change T1, T2, and T3 somewhat and to enhance the temperature difference between T3 and melting. After the complete reaction of BCSCO, heating to or cooling from the melting temperature did not result in any weight loss, in contrast to the 90K LM2Cu3O6+0 superconductors. This suggests possible greater chemical stabilities of BCSCO
than LM2Cu3O6+0 superconductors.
Bar samples were cut from sintered BCSCO pellets. A
four-lead method was employed for the resistance measurements and a PAR Model M155 vibrating sample magnetometer was used for investigating magnetization.
The temperature dependence of resistance (R) for these samples and magnetization (M) for BCSCO-a and -c appear in Figures 2 and 3, respectively.
Only one superconducting transition was observed in BCSCO-a, but two occur in BCSCO-b and BCSCO-c (Figure 2).
The magnetization measurements represented in Figure 3 show that 12% of the Meissner effect in these samples is associated with a 115K transition. The total Meissner effect of the samples is about 40% compared to a Pb sample of similar size. The only partial Meissner effect may be attributed to the multiphase nature and/or low flux trapping of the BCSCO sample. Greater Meissner effects (up to 60%) have been detected in other BCSCO samples; in some specimens as much as two-thirds of the effect is associated with the 115K transition.
X-ray powder diffraction patterns of the Cu-rich BCSCO-c sample revealed a substantial amount of unreacted copper oxide, which was not present in BCSCO-a or -b.
Samples were examined by optical and electron microscopy, x-ray powder and single-crystal diffraction, and electron microanalysis. Powder x-ray diffration patterns were made on a Rigaku DMAX-3B automated diffractometer.
Single-crystal x-ray diffraction was performed on a Rigaku automated four-circle diffractometer with monochromated rotating anode Mo source. Electron microanalyses were obtained on a JSM 35 scanning electron microscope, operated at 20 KV and 0.01 pm spot size. Standards included pure Bi and Cu metal, Sr-bearing glass and a diopside jadeite pyroxene. A Phillips EM420 transmission electron microscope with EDAX, Si-Li detector, and a Princeton Gamma-Tech 4 data analysis system was employed. TEM samples were mounted on holey-carbon Be-mesh grids to avoid Cu-contaimination during qualitative analysis.
The BCSCO samples comprised at least four phases, two phases were alkaline earth copper oxides, another phase was a bismuth alkaline earth oxide, and the four phase was the superconductor phase. Elongated subhedral to euhedral crystals of a tranparent, birefringent, pleochroic (red to colorless) phase was prominent in grain mounts of all three of the BCSCO (a,b, and c) samples examined with a polarizing microscope. Needle-like crystals up to 100 Iim long, though abundant in some samples, constitute a small fraction (probably less than 5%) of the sample volume.
Electron microanalysis of five different crystals of this insulating phase yields an average composition of (Ca Sr )2(Cu Bi )03. Some or all of the bismuth 0.92 0.08 0.96 0.3 may represent background secondary scattering from adjacent Bi-rich phases; therefore, this crystalline phase may be bismuth free. A 90 x 10 x 5 pim crystal was selected for single-crystal x-ray diffraction study and was found to have orthohombic symmetry with a = 12.234, b = 3.777 and c = 3.257 A. These values are almost identical to those reported for stoichiometric Ca2CuO3 by *trade mark Teske and Mtlller-Buschbaum Z. Anorg. Alle. Chem., 379, 234 (1970).
A second bismuth-poor phase, distinguished in grain mounts as black, opaque, elongated euhedral to subhedral grains up to 60 pm long, was found in samples BCSCO-b and BCSCO-c to have a composition of approximately (Cao.6Sro.4)Cu1.7503 based on microanalysis of four grains.
Approximately 0.03 atoms of bismuth were also detected per one alkaline earth cation. Three crystals of this phase were examined by single-crystal x-ray techniques. Though the stoichiometry is similar to CaCu203r the unit cell and structure differ from those reported by Teske and Moller-Buschbaum, Z. Anorg. Alle. Chem., 370, 134 (1969) for the pure calcium copper oxide. Standard indexing procedures yielded an F-centered orthorhombic unit cell-o with a = 11.328, b = 12.774 and c = 3.896 A for all three crystals. Striations characteristic of twinning and peak splittings were observed for these grains, however, and it is likely that the symmetry is monoclinic.
A third minor phase, distinguished by a composition enriched in bismuth and lacking in copper, was observed by electron microanalysis in sample BCSCO-a. The composition, based on analyses of three different equant grains and normalized to one Bi, is (Ca Sr )BiO
0.45 0.39 3-a Two poorly-resolved electron diffraction patterns were obtained for this phase; one revealed an orthogonal net approximately 10.5 x 3.0 A and the other shows a 9.5 A
spacing with faint intermediate supercell reflections, possibly characteristic of a 19.0 A repeat. The structure of this phase may be related to strontium bismuth oxide Sro=9Bi1.102=55, a tetragonal phase with a = 13.329 and c = 4.257 A which was described by Guillermo et al Rev. Chim. Miner., 15, 153 (1978). That phase displayed characteristic spacings of 9.30 A (110 and 3.06 A (301).
The fourth phase, which is the superconducting compound, was abundant in all three samples. It was _18- 1341621 distinguished by a layered structure probably related to the class of layered bismuth compounds described by Aurivillus Arkiv. Kemi, 1, 463 and 499 (1950). These structures incorporate both perovskite-type layers and unusual Bi202 layers of bismuth in distorted four coordination. Transmission electron microscopy (TEM) revealed that the grains possessed a perfect basal (hereafter termed 001) cleavage, similar to that of clay minerals. The structure, therefore, must consist of a layered atomic arrangement with planes of weak bonding.
Electron diffraction in the TEM of the (001) layers is facilitated by the tendency of almost every grain to lie flat on the holey carbon film. Numerous (hkO) electron diffraction patterns were obtained (Figure 4), all of which show a prominent perovskite-like 2.7 x 2.7 A subcell and a distinctive 5.41 x 27.2 A supercell. A few grains, lying near the edge of the grid, were found to be oriented with (001) layers perpendicular to the grid. From these crystallites a stacking periodicity of 15.39 A was observed (Figure 5). High-resolution images of these grains clearly revealed a four-layer structure with a 3.86 A subcell (Figure 5). The image contrast of these layers suggests a possible ABAC-ABAC repeat pattern.
A single grain oriented with a perpendicular to the gird yielded an electron density pattern corresponding to a 5.44 x 30.78 A centered lattice with a 5-repeat (27.2 A) superlattice parallel to b (Figure 6). High-resolution images of this plane showed a "brick-like pattern characteristic of the A-centered structure, as well as numerous stacking faults and other defects. Many of these defects are probably associated with interfaces between perovskite and the Bi202 modules, both of which display approximately 3.8 A layer spacings.
The TEM initial cell parameters were used to index 26 lines in the complex x-ray powder pattern (Table 1). Note that the moderately strong 001 line at 15.4 A provides a useful marker for this phase. Refined orthorhombic lattice constants based on the powder diffraction lines were a = 5.410 0.003.b = 5.439 0.005 (x 5), and c =

30.78 0.03 A. These parameters are related to the simple cubic perovskite cell (a cube with a = 3.85 A) by the ratios ,/2 x 5V2 x 8.
The superconductor phase occurs in fine-grained masses of black, opague flattened crystallites. The' average diameter of these thin plates is less than 5 pm and the thickness is usually less than 0.1 pm. Polished scanning electron microscopy (SEM) mounts revealed that this phase forms a matrix of randomly-oriented interlocking flakes in which the other single-crystal phases "float." This texture implies that the superconducting phase crystallized last, at a lower temperature than the other phases. The average composition of the superconductor was determined from 15 analyses from three different samples. The ratio of cations approximates 2:1:2:2 for Bi:Ca:Sr:Cu. The average formula may be represented more precisely as Bi2(Sr 0 56 Ca 0 39 Bi 0 05 ) 3 Cu2O8+8. Note that bismuth can form a solid solution with strontium and calcium in some structures. Analysis totals, based on oxides and assuming divalent copper and trivalent bismuth, totaled approximately 97%. It is likely, therefore, that some of the copper or bismuth are in higher oxidation states.
Considerable variability of composition is observed from grain to grain. The ratio of total (Cu + Bi) to total (Ca + Sr) is relatively constant at 1:00:0.68 0.02.
The ratio of Cu to Bi, however, ranges from 40:60 to 49:51, with most compositions closer to the latter value.
The Sr:Ca ratio ranges from 38:30 to 43:25 with an average value of 40:28. Some of these variations may result from microscopic inclusions of other phases or from secondary scattering from adjacent grains. It seems likely, however, that the superconducting phase has a variable composition with Bi-Ca-Sr solid solution. Furthermore, the presence of numerous defects and stacking faults provides an additional mechanism for incorporating composition variation. These variations may account for the differences between the superconductivity behavior displayed by the three samples.
The new structure high temperature superconductor Bi2CaSr2Cu20g (g is 8 to 9) is closely related to the 22 K
superconducting phase described by Michel et al, Z. Phys., B.68, 421 (1987) which has an approximate formula Bi2Sr2Cu2O7 and unit cell parameters 5.32 x 26.6 x 48.8 A.
Both the Michel material and the new phase structure display a distinctive b superlattice behavior, both have a prominent layered habit, and both possess long c-axis repeats. The new phase structure appears to be distinct, however, based on the different c-axis repeat and differences in the x-ray powder diffraction patterns.
A detailed description of the complex perovskite related structure of the new material will not be possible without improved powder diffration data, coupled with high-resolution imaging of the lattice by TEM. Such studies are now in progress. Nevertheless, several structural inferences can be drawn from the compositional, powder X-ray and TEM data already obtained. A
one-dimensional electron density profile is calculated based on the observed powder diffraction intensities of 001 reflections. This analysis indicates a pronounced layering of cations in (001), with substantial deviations from the ideal perovskite arrangement of metal atoms.
Bismuth appears to be concentrated in layers, perhaps similar to the Bi202 slabs of phases such as BaBi4Ti4015.
Weak electron density associated with every fourth layer of the structure suggests interlayer regions of weak bonding. It may be speculated that copper and oxygen adopt the planar configuration common to the other known high-temperature oxide superconductors, but there is not yet any direct evidence to support this supposition.
Superstructures parallel to the a and b axes may be the result of cation and oxygen ordering. Note, that electron diffraction patterns reveal extensive streaking along c and b, as well as spot splitting, twinning, stacking faults and other defects that will likely disrupt most linear structures, if the latter exist. If these features affect superconductivity then annealing conditions and oxygen content should have an important effect on the temperature and sharpness of the superconducting transitions. The numerous structural defects provide a mechanism for incorporating compositional variations, as well as for generating numerous closely-related homologous structures with slightly larger or smaller superstructure.
In spite of the extremely fine-grained texture and high density of defects, the copper-oxygen layers appear to be continuous over hundreds of unit cells. This layered structure may possess one significant advantage in terms of processing and applications. Fabrication of the superconductor by compression into planes yield superconductor components with enhanced properties (e.g., critical current) in a specific plane. Similarly, fabrication by rolling could produce wires more flexible than those of ordinary ceramic materials.
Table II below gives the data obtained by a powder x-ray analysis of the superconducting Bi-Ca-Sr-Cu oxide phase. Patterns were obtained with filtered Cu radiation.
Pure silicon (NBS Standard References material 640) was used as an internal standard.

TABLE II

Powder diffraction pattern for the Bi-Ca-Sr-Cu oxide superconductor, based on a subcell 5.410 x 4.439 x 30.78 A
h k 1 dohs dcacl I/10 0 0 2 15.66 15.39 12 0 1 1 5.361 5.359 5 0 0 8 3.857 3.847 23 1 0 6 3.736 3.723 3 1 1 3 3.593 3.594 41 1 1 5 3.257 3.256 100 0 0 10 3.085 3.080 24 1 1 7 2.890 2.891 62 2 0 0 2.709 2.705 91 2 0 2 2.668 2.664 19 0 0 12 2.556 2.565 18 2 1 1 2.413 2.415 5 2 0 8 2.214 2.213 4 0 0 14 2.200 2.199 3 2 0 10 2.033 2.032 26 1 1 13 2.013 2.015 11 2 1 9 1.978 1.977 4 2 2 0 1.915 1.918 31 2 2 4 1.862 1.862 9 1 1 15 1.809 1.809 13 0 3 3 1.787 1.786 3 3 1 3 1.687 1.689 5 3 1 5 1.648 1.649 13 3 0 8 1.634 1.633 7 3 1 7 1.595 1.595 13 3 1 9 1.531 1.531 10 Figure 4 illustrates selected-area electron diffraction pattern of the Bi-Ca-Sr-Cu oxide superconductor showing hk0 diffraction spots. Strong spots correspond to 2.7 x 2.7A subcell, while superlattice reflections along a and b indicate spacings of 5.4 and 27.1 A respectively.
Figure 5 illustrates selected-area electron diffraction pattern of the 00k diffraction row, which is streaked but shows a strong 15.4 A periodicity. The 004 diffraction is indicated.
Figure 5 also illustrates a high-resolution image taken parallel to the layers shows the 15.4 A(001) spacing, with subspacings of 3.8 A. The contrast of these layers differs, suggesting a possible ABAC-ABAC type stacking of perovskite units. A structural defect (arrowed) may correspond to a Bi-free region of CaSr-Cu perovskite.
Figure 6 illustrates the selected-area Ok2 electron diffraction pattern is characterized by an A-centered 27 x 31 A lattice.
Figure 6 also illustrates a high-resolution image of the (100) plane reveals numerous stacking faults and defects as well as the A-centered layered structure.
Though most of the structure appears to be orthogonal, locally inclined blocks may indicate a fine-scale twinning or may represent "monoclinic" regions of related but different structure.
BCSCO is a quinary superconducting compound system, consisting of the trivalent Bi. Structural data shows that the 90K-transition in BCSCO is associated with the Bi2CaSr2Cu2O8+0 (2:1:2:2) phase. A single phase BCSCO
sample with a TC-120K has yet to be obtained for detailed physical characterization.
X-ray powder diffraction was carried out on more than 45 BCSCO samples of different compositions prepared under different conditions. By comparing the X-ray data with the electrical and magnetic results, the diffraction -24- 1 3 4 1 f1 2 1 pattern for the superconducting phase was isolated as shown in Fig. 7. No difference has been detected yet within the resolution limits of the instrument used between samples with Tc's between 60K and 120K. Results for BCSCO-b synthesized at various temperatures slightly higher than T1, T2, and T3 are also displayed in Figure 7.
It is clear that the superconducting phase starts to grow slowly at temperatures above T1, then rapidly above T1.
The basic pattern of the superconducting phase appears in samples for Cu to Bi ratio varying from -0.8 to 6.0 in the fashion mentioned above. For example, when the insulating Ca2CuO3 was doped with only a few percent of Bi and Sr, the sample became completely superconducting resistively below 60K and the superconducing phase appeared in the X-ray diffraction pattern. A Cu-rich sample BCSCO-c (with a composition ration of 1:22:14:6.2) synthesized at 850 C
was also studied. The X-ray data showed that a great majority of the sample belonged to the superconducting phase, in spite of the samll amount of Bi. Synthesis in a pure oxygen atmosphere was found to be detrimental to the superconducting properties of BCSCO, probably due to the conversion of Bi+3 to Bi+S. It even made the sample paramagnetic.
Typical resistance (R) and magnetization (M) results are shown respectively in Figs. 8 and 9 for BCSCO-b, synthesized at different temperatures. It is clear that both the Tc and the Meissner effect grow as the synthesis temperature increases. The 120K transition occurs only when the sample is synthesized above -850K, although lower Tc happens in samples prepared at lower temperatures.
However, the superconducting properties deteriorate when the sample is heated above the melting point. In these two figures, results for BCSCO-c are also shown. A trace of the 120K-transition is evident although the bulk of the sample is superconducting at -85K. It should be noted that the porosity of the samples can be rather different.
This is particularly true for samples displaying a large transition at -120K, i.e., it is very fluffy. Therefore no effort was made to extract resistivity or to calculate M per volume.
The magnetic field effect of R for a BCSCO-b sample is shown in Fig. 10. The transition is clearly suppressed to lower temperature and broadened in the presence of magnetic field. The broadening is similar to that observed in LBa2Cu3O6+0 polycrystalline compounds due to the weak coupling between the highly anisotropic structure of the compounds. The upper critical field at 0 K for the 120K transition is estimated to be -187T.
From the above R-and M-results, samples with a single superconducting transition at -90K or below can be obtained rather easily. However, no sample has exhibited only one complete transition at -120K. In view of the-large fraction of the Meissner effect associated with this 120K transition, the failure to achieve a complete resistive transition at this high temperature suggests that the 120K Tc material must be enclosed by the 90K Tc material. This is in strong contrast to the LBa2Cu3O6+M
compounds or even the low Tc BCSCO superconductors. On the other hand, the appearance of two resistive superconducting transitions is similar to the A-15 superconducting compounds. The drastic difference between the morphologies of the high Tc BCSCO compounds and the 22K Bi2Sr2Cu2O7 compound mentioned earlier indicate that there exists a difference between their growth processes.
Careful studies on the reaction kinetics and the phase diagram of BCSCO is needed to achieve single transition sample with Tc-120K. High temperature annealing for more than 24 hours has not enhanced the signal size.
The structure study showes that the BCSCO material with compositions 2:1:2:2 superconduct at -90K have a four-layer structure, although the exact atomic arrangement is yet to be determined. Numerous structural defects have been observed in microcrystalites of this compound and have been suggested to be responsible for the existence of a large homogeneity range in BCSCO. The high Tc phase, i.e. -120K, may have a homologous structure closely related to the 2:1:2:2 phase. This is consistent with the observation of similar X-ray diffraction patterns of samples with Tc ranging from 40 to 120K. Single crystals with a Tc-90K have been obtained and investigated.
The Tc of BCSCO compositions depends sensitively on the synthesis temperature but not on the Cu to Bi ratio.
High Tc phase appears only for samples prepared at temperatures above 850 C but below melting. The present study also demonstrates that there exists a large homogeneity range for the superconducting phase to form, preferably in a Cu-rich environment. This raises questions concerning the essential role of planar configuration of Cu-ions in BCSCO. The 120K-transition phase may possess a homologous structure of the newly identified 2:1:2:2 90K phase. Even higher Tc may be achievable in this system with increasing complexity in crystal chemistry.

Claims (23)

1. A material which is superconductive at a temperature of 77°K or higher, said material comprising a multiphase oxide of nominal composition M*a A*b O y wherein M*
is a mixture of divalent alkaline earth metals selected from the group consisting of Ba, Sr, and Ca wherein the,ratio of the alkaline earth metal of larger atomic radius to the alkaline earth metal of smaller atomic radius is from about 1:1 to about 3:1; A* is a mixture of Cu and a trivalent metal selected from the group consisting of Bi and Ti wherein the molar ratio of Cu to said trivalent metal is from about 1:1 to about 3:1; "a" is 1 to 2; "b" is 1; and "y" is 2 to 4.

2. The material of claim 1 wherein M* is a 1:1 mixture of Ca and Sr and "a" is 1.

3. A material which is superconductive at a temperature of 77°K or higher, up to about 90°K, said material comprising a multiphase oxide of nominal composition BiCaSrCuO2y wherein "y" is 2 to 4 and having a sufficient quantity of a crystalline phase composition of a formula Bi2CaSr2Cu2Og wherein "g" is a value from about 8 to about 9 which provides said crystalline phase composition with zero electrical resistance at a temperature of 77°K or higher, up to about 90°K, to cause the material to exhibit zero electrical resistance at a temperature of 77°K or higher, up to about 90°K.

4. An oxide composition of nominal formula T d M* e Cu f O g wherein "T" is Bi or T1; "M*" is a mixture of divalent alkaline earth metals selected from the group consisting of Ba, Sr, and Ca wherein the ratio of the alkaline earth metal of larger atomic radius to the alkaline earth metal of smaller atomic radius is from about 1 to about 3; "d" is a number from about 1 to about 3; "e" is a number from about 1 to about 6; "f" is a number from about 1 to about 6; and "g"
is a number from about 0.5 (3d + 2e + 2f) to about 0.5 (3d + 2e + 3f) that provides the oxide composition with zero electrical resistance at a temperature of 77°K or higher.

5. The oxide composition of claim 4 wherein "T" is Bi; "M*" is a 1:2 mixture of Ca and Sr; "d" is 2; "e" is 3;
"f" is 2 and "g" is a value between about 8 to about 9.

6. The material of claim 1 wherein M* is a 1:1 mixture of Ca and Sr; A* is a 1:1 mixture of Cu and Bi and a is 1.

7. The material of claim 1 wherein A* is T1.

8. The material of claim 1 wherein A* is Bi.

9. The material of claim 1 wherein said material is of a perovskite crystalline form.

10. The material of claim 1 wherein said trivalent metal has an atomic radius between about 1.5 A and about 2.1 A.

11. A crystalline phase oxide composition comprising cations of Bi, Ca, Sr, and Cu approximating the ratio of 2:1:2:2 for Bi:Ca:Sr:Cu and which exhibits zero electrical resistance at a temperature of 77°K or higher.

12. The composition of claim 11 wherein said crystalline phase composition is of the formula Bi2Ca1Sr2Cu2O g wherein g is 8 to 9.

13. A superconducting oxide composition of nominal formula T dM*eCu fO g wherein "T" is Bi or T1 ; "M*" is a mixture of divalent alkaline earth metals selected from the group consisting of Ba, Sr, and Ca wherein the ratio of the alkaline earth metal of larger atomic radius (M L) to the alkaline earth metal of smaller atomic radius (M S) is from about 1 to about 3; "d" is a number from about 1 to about 3;
"e" is a number from about 1 to about 6; "f" is a number from about 1 to about 6; and "g" is a number from about 0.5 (3d +
2e + 2f) to about 0.5 (3d + 2e + 3f) that provides the oxide composition with zero electrical resistance at a temperature of 77°K or higher, wherein said composition is made by a process comprising the steps of:
compressing a mixture of solid powdered compounds comprising:

(a) T2O3 (b) M LCO3 or M LO
(C) M SCO3 or M SO and (d) CuO
in proportions appropriate to yield said formula;
heating the compressed powder mixture to a temperature of from about 800°C to about 950°C for a time sufficient to complete the solid state reaction; and quenching said reacted compressed mixture to room temperature.

14. The oxide composition of claim 13 wherein "T" is Bi; "M*" is a 1:2 mixture of Ca and Sr; "d" is 2: "e" is 3;
"f" is 2 and "g" is a value between about 8 and 9.

15. A material which is superconductive at a temperature of 77°K or higher, said material comprising a multiphase oxide of nominal composition M*aA*bO y wherein M*
is a mixture of divalent alkaline earth metals selected from the group consisting of Ba, Sr, and Ca wherein the,ratio of the alkaline earth metal of larger atomic radius to the alkaline earth metal of smaller atomic radius is from about 1:1 to about 3:1; A* is a mixture of Cu and a trivalent metal, Bi wherein the molar ratio of Cu to said trivalent metal is from about 1:1 to about 3:1; "a" is 1 to 2; "b" is 1;
and "y" is 2 to 4.

16. The material of claim 15 wherein M* is 1:1 mixture of Ca and Sr and "a" is 1.

17. An oxide composition of nominal formula T dM*Cu fO g wherein "T" is Bi; "M*" is a mixture of divalent alkaline earth metals selected from the group consisting of Ba, Sr, and Ca wherein the ratio of the alkaline earth metal of larger atomic radius to the alkaline earth metal of smaller atomic radius is from about 1 to about 3; "d" is a number from about 1 to about 3; "e" is a number from about 1 to about 6; "f" is a number from about 1 to about 6; and "g"
is a number from about 0.5 (3d + 2e + 2f) to about 0.5 (3d + 2e + 3f) that provides the oxide composition with zero electrical resistance at a temperature of 77°K or higher.

18. The oxide composition of claim 17 wherein "M*" is "d" is 2; "e" is 3; "f" is 2 a 1:2 mixture of Ca and Sr;
and "g" is a value between about 8 to about 9.

19. The material of claim 15 wherein M* is a 1:1 mixture of Ca and Sr; A* is a 1:1 mixture of Cu and Bi and a is 1.

20. The material of claim 15 wherein said material is of a perovskite crystalline form.

21. The material of claim 15 wherein said trivalent:
metal has an atomic radius between about 1.5 A and about 2.1 A.

22. A superconducting oxide composition of nominal.

formula T dM*eCu fO g wherein "T" is Bi; "M*" is a mixture of divalent alkaline earth metals selected from the group consisting of Ba, Sr, and Ca wherein the ratio of the alkaline earth metal of larger atomic radius (M L) to the alkaline earth metal of smaller atomic radius (M S) is from about 1 to about 3; "d" is a number from about 1 to about 3;
"e" is a number from about 1 to about 6; "f" is a number from about 1 to about 6; and "g" is a number from about 0.5 (3d +
2e + 2f) to about 0.5 (3d + 2e + 3f) that provides the oxide composition with zero electrical resistance at a temperature of 77°K or higher, wherein said composition is made by a process comprising the steps of:
compressing a mixture of solid powdered compounds comprising:

(a) T2O3 (b) M LCO3 or M LO
(C) M SCO3 or M SO and (d) CuO
in proportions appropriate to yield said formula;
heating the compressed powder mixture to a temperature of from about 800°C to about 950°C for a time sufficient to complete the solid state reaction; and quenching said reacted compressed mixture to room temperature.

23. The oxide composition of claim 22 wherein "M*" is a 1:2 mixture of Ca and Sr; "d" is 2; "e" is 3;
"f" is 2 and "g" is a value between about 8 and 9