Compositions: ceramic – Ceramic compositions – Refractory
Patent
1990-11-08
1997-09-09
Bell, Mark L.
Compositions: ceramic
Ceramic compositions
Refractory
505782, 505121, 505125, 505501, C01F 1102, H01L 3912
Patent
active
056656629
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention is directed to a high-temperature superconductor of the system Bi--Sr--Ca--Cu--O.
Bednorz and Mueller disclosed superconductors based on lanthanum-strontium-copper oxide that have a high transition temperature of the transition from normal conduction into superconduction that was hitherto never achieved. Transition temperatures achieved for yttrium-barium-copper oxide systems lie at 70 through 90 K. Another system, bismuth-strontium-calcium-copper oxide recently has been disclosed and is currently under intensive investigations. The influence of the sintering parameters such as sintering temperature, sintering duration and partial oxygen pressure during the sintering process have been investigated.
The manufacture of the material cited second above proceeds based on the pulverization of initial nominal materials that are mixed, ground and cold-pressed. The sintering ensues in microprocessor-controlled furnaces, whereby the material is placed on zirconium oxide plates. Sintering temperatures that are applied when sintering in air lie at 800.degree., 860.degree., 880.degree., 900.degree. C., whereby the sintering is performed for a duration of ten hours.
Gold contacts are applied to the resultant materials for measuring the electrical properties. The magnetic properties of a respective material are identified by measuring the inductivity of a coil that surrounds the material.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a the chemical composition of high-temperature superconductor material that has a high transition temperature above 90 K.
This object is achieved with a material based on the Bi--Sr--Ca--Cu--O system having the nominal composition: O.sub.10+d (d=delta)
BRIEF DESCRIPTION OF THE DRAWINGS
The FIGURE illustrates a portion of the layer sequence of a superconducting structure of the present invention.
DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS
The present invention is based on the following observations: the system BiSrCaCu.sub.2 O.sub.x -(-) (this formula represents the nominal composition. The dependency of the zero resistance on the temperature was measured between 55 and 175 K. The curve of the dependency between zero resistance and temperature exhibited two stages of the drop in resistance for the material, that had been sintered for ten hours in air at temperatures from 860 through 880.degree. C. Appropriate linear extrapolation yielded values of between 100 and 105 K. for a superconducting phase transition.
This result was reproducible and was also very pronounced for specimens having longer sintering time. Semiconductor behavior was observed for specimens having sintering temperatures of 900.degree. C. and above.
Other investigations were performed pursuant to the present invention and were directed to developing a material from the investigated material having two-phase or a multi-phase structure whose composition provided a transition temperature between 100 and 105 K.
The invention is based on the further observation that the above-recited material is multi-phase and a co-existence of two superconductor materials is present therein, whereof the one material has the recited, high transition temperature.
The inventor has succeeded in discovering that such a material having a transition temperature of approximately 105 K. is that material that is at least composed of a high majority of only one phase of the system bismuth-strontium-calcium-copper oxide, particularly having a partial bismuth substitution by lead. It is known from Science, Volume 239 (February 1988), pages 1015/1016, particularly FIG. 3, that the superconducting material of the system having a nominal composition of bismuth oxide-strontium-calcium-copper oxide has a layer structure with alternating bismuth oxide layers on the one hand and sequences of layers of strontium/copper/calcium(strontium)/copper/strontium oxide on the other hand.
The inventor has found that a phase having the lattice constants of a=0.54 nm and
REFERENCES:
patent: 4880771 (1989-11-01), Cava et al.
Liu, et al, "Crystal Growth and Superconductivity in the Bi-Ca-Sr-Cu-O System", Physics Letters A, vol. 127 No. 8.9, Mar. 14, 1988, pp.444-446.
Kang, et al, "Superconductivity in Thin Films of the Bi-Ca-Sr-Cu-O System" Physics Letters A, vol. 128, No. 1.2, Mar. 21, 1988, pp.102-104.
Anil Khurana, "The T.sub.c to Beat is 125 K", Search & Discovery, Apr. 1988, pp. 21-25.
Tarascon, et al "Crystal Substructure and Physical Properties of the Superconducting Phase Bi.sub.4 (Sr,Ca).sub.6 Cu.sub.4 O.sub.16+x " Physical Review B, vol. 37,No. 16, pp.9382-9388.
Kijima, et al "Identification of a High T.sub.c Superconducting Phase, et al," Japanese Jornal of Applied Physics, vol. 27, No. 3, Mar. 1988, pp. L369-L371.
Muromachi, et al "Identification of the Superconducting Phase, etc", Japanese Journal of Applied Physics, vol. 27, No. 3, Mar. 1988, pp. L365-L368.
Komatsu, et al "Preparation of High T.sub.c Superconducting, etc.," Japanese Jornal of Applied Physics, vol. 27, No. 4, Apr. 1988, pp. L533-L535.
Matsui, et al "High-Resolution Electron Microscopy, etc", Japanese Jornal of Applied Physics, vol. 27, No. 3, Mar. 1988, pp. L361-L364.
Nach. Chem. Tech. Lab. vol. 36-No. 4, Apr. 1988.
Cava, et al "Studies of Oxygen Deficient, etc", North Holland Physics, pp. 560-565. *no date.
Chu, et al "Superconductivity up to 114 K, etc", Physical Review Letters, vol. 60, No. 10, Mar. 7, 1988, pp. 941-943.
Adachi et al. "Superconductivity Properties in a Bi-Sr-Ca-Cu-O System", Jap. J. App. Phy., vol. 27, Mar. 1988, pp. L344-46.
Chu et al, "Superconductivites up to 114k in the Bi-Al-Ca-Sr-Cu-O Compound" Phy Rev Lett. vol. 60, #10, 7 Mar. 1988.
Bell Mark L.
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