Process for making superconductors using barium hydroxide

There is disclosed an improved process for preparing a superconducting composition having the formula M.sub.w A.sub.z Cu.sub.v O.sub.x wherein M is selected from the group consisting if Bi, Tl, Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm Yb and Lu; A is at least one alkaline earth metal selected from the group consisting of Ba, Ca and Sr; x is at least 6; w is at least 1; z is at least 2 and v is at least 1; said composition having a superconducting transition temperature of above 77 K, preferably above about 90 K; said process consisting essentially of (a) forming a suspension having an M:A:Cu atomic ratio of w:z:v by mixing A(OH).sub.2, AO or AO.sub.2 and M.sub.2 O.sub.3 with an aqueous solution of cupric carboxylate or cupric nitrate at a temperature from about 50.degree. C. to about 100.degree. C., or mixing A(OH).sub.2 with an aqueous solution of Cu carboxylate, nitrate or a mixture thereof and M carboxylate, nitrate or a mixture thereof at a temperature from about 50.degree. C. to about 100.degree. C.; (b) drying the suspension formed in step (a) to obtain a precursor powder; and (c) heating and cooling the powder under specified conditions to form the desired superconducting composition. Shaped articles thereof are also disclosed.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an improved process for making copper 
oxide-containing superconductors. 
2. Description of Related Art 
Bednorz and Muller, Z. Phys. B64, 189-193 (1986), disclose a 
superconducting phase in the La-Ba-Cu-O system with a superconducting 
transition temperature of about 35 K. Samples were prepared by a 
coprecipitation method from aqueous solutions of Ba-, La- and Cu-nitrate 
in their appropriate ratios. An aqueous solution of oxalic acid was used 
as the precipitant. Chu et al., Phys. Rev. Lett. 58, 405-407 (1987), 
report detection of an apparent superconducting transition with an onset 
temperature above 40 K. under pressure in the La-Ba-Cu-O compound system 
synthesized directly from a solid-state reaction of La.sub.2 O.sub.3, CuO 
and BaCO.sub.3 followed by a decomposition of the mixture in a reduced 
atmosphere. Chu et al., Science 235, 567-569 (1987), disclose that a 
superconducting transition with an onset temperature of 52.5 K. has been 
observed under hydrostatic pressure in compounds with nominal compositions 
given by (La.sub.0.9 Ba.sub.0.1).sub.2 CuO.sub.4-y, where y is 
undetermined. They state that the K.sub.2 NiF.sub.4 layer structure has 
been proposed to be responsible for the high-temperature superconductivity 
in the La-Ba-Cu-O system (LBCO). They further state that, however, the 
small diamagnetic signal, in contrast to the presence of up to 100% 
K.sub.2 NiF.sub.4 phase in their samples, raises a question about the 
exact location of superconductivity in LBCO. Cava et al., Phys. Rev. Lett. 
58, 408-410 (1987), disclose bulk superconductivity at 36 K. in La.sub.1.8 
Sr.sub.0.2 CuO.sub.4 prepared from appropriate mixtures of high purity 
La(OH).sub.3, SrCO.sub.3 and CuO powders, heated for several days in air 
at 1000.degree. C. in quartz crucibles. Rao et al., Current Science 56, 
47-49 (1987), discuss superconducting properties of compositions which 
include La.sub.1.8 Sr.sub.0.2 CuO.sub.4, La.sub.1.85 Ba.sub.0.15 
CuO.sub.4, La.sub.1.8 Sr.sub.0.1 CuO.sub.4, (La.sub.1-x Pr.sub.x).sub.2-y 
Sr.sub.y CuO.sub.4, and (La.sub.1.75 Eu.sub.0.25)Sr.sub.0.2 CuO.sub.4. 
Bednorz et al., Europhys. Lett. 3, 379-384 (1987), report that 
susceptibility measurements support high-T.sub.c superconductivity in the 
Ba-La-Cu-O system. In general, in the La-Ba-Cu-O system, the 
superconducting phase has been identified as the composition La.sub.1-x 
(Ba,Sr,Ca).sub.x CuO.sub.4-y with the tetragonal K.sub.2 NiF.sub.4 -type 
structure and with x typically about 0.15 and y indicating oxygen 
vacancies. 
Wu et al., Phys. Rev. Lett. 58, 908-910 (1987), disclose a superconducting 
phase in the Y-Ba-Cu-O system with a superconducting transition 
temperature between 80 and 93 K. The compounds investigated were prepared 
with nominal composition (Y.sub.1-x Ba.sub.x).sub.2 CuO.sub.4-y and x=0.4 
by a solid-state reaction of appropriate amounts of Y.sub.2 O.sub.3, 
BaCO.sub.3 and CuO in a manner similar to that described in Chu et al., 
Phys Rev. Lett. 58, 405-407 (1987). Said reaction method comprises more 
specifically heating the oxides in a reduced oxygen atmosphere of 
2.times.10.sup.-5 bars (2 Pa) at 900.degree. C. for 6 hours. The reacted 
mixture was pulverized and the heating step was repeated. The thoroughly 
reacted mixture was then pressed into 3/16 inch (0.5 cm) diameter 
cylinders for final sintering at 925.degree. C. for 24 hours in the same 
reduced oxygen atmosphere. The material prepared showed the existence of 
multiple phases. 
Hor et al., Phys. Rev. Lett. 58, 911-912 (1987), disclose that pressure has 
only a slight effect on the superconducting transition temperature of the 
Y-Ba-Cu-O superconductors described by Wu et al., supra. 
Sun et al., Phys. Rev. Lett. 58, 1574-1576 (1987), disclose the results of 
a study of Y-Ba-Cu-O samples exhibiting superconductivity with transition 
temperatures in the 90 K. range. The samples were prepared from mixtures 
of high-purity Y.sub.2 O.sub.3, BaCO.sub.3 and CuO powders. The powders 
were premixed in methanol or water and subsequently heated to 100.degree. 
C. to evaporate the solvent. Two thermal heat treatments were used. In the 
first, the samples were heated in Pt crucibles for 6 hours in air at 
850.degree. C. and then for another 6 hours at 1000.degree. C. After the 
first firing, the samples were a dark-green powder, and after the second 
firing, they became a very porous, black solid. In the second method, the 
powders were heated for 8-10 hours at 1000.degree. C., ground and then 
cold pressed to form disks of about 1 cm diameter and 0.2 cm thickness. 
The superconducting properties of samples prepared in these two ways were 
similar. X-ray diffraction examination of the samples revealed the 
existence of multiple phases. 
Cava et al., Phys. Rev. Lett. 58, 1676-1679 (1987), have identified this 
superconducting Y-Ba-Cu-O phase to be orthorhombic, distorted, 
oxygen-deficient perovskite YBa.sub.2 Cu.sub.3 O.sub.9-.delta. where 
.delta. is about 2.1, and have presented the X-ray diffraction powder 
pattern and lattice parameters for the phase. The single-phase YBa.sub.2 
Cu.sub.3 O.sub.9-.delta. was prepared in the following manner. BaCO.sub.3, 
Y.sub.2 O.sub.3 and CuO were mixed, ground and then heated at 950.degree. 
C. in air for 1 day. The material was then pressed into pellets, sintered 
in flowing O.sub.2 for 16 hours and cooled to 200.degree. C. in O.sub.2 
before removal from the furnace. Additional overnight treatment in O.sub.2 
at 700.degree. C. was found to improve the observed properties. 
Takita et al., Jpn. J. Appl. Phys. 26, L506-L507 (1987), disclose the 
preparation of several Y-Ba-Cu compositions with superconducting 
transitions around 90 K. by a solid-state reaction method in which a 
mixture of Y.sub.2 O.sub.3, CuO, and BaCO.sub.3 was heated in an oxygen 
atmosphere at 950.degree. C. for more than 3 hours. The reacted mixture 
was pressed into 10 mm diameter disks for final sintering at 950.degree. 
or 1000.degree. C. for about 3 hours in the same oxygen atmosphere. 
Takabatake et al., Jpn. J. Appl. Phys. 26, L502-L503 (1987), disclose the 
preparation of samples of Ba.sub.1-x Y.sub.x CuO.sub.3-z (x=0.1, 0.2, 
0.25, 0.3, 0.4, 0.5, 0.6, 0.8 and 0.9) from the appropriate mixtures of 
BaCO.sub.3, Y.sub.2 O.sub.3 and CuO. The mixture was pressed into a disc 
and sintered at 900.degree. C. for 15 hours in air. The sample with x=0.4 
exhibited the sharpest superconducting transition with an onset near 96 K. 
Syono et al., Jpn. J. Appl. Phys. 26, L498-L501 (1987), disclose the 
preparation of samples of superconducting Y.sub.0.4 Ba.sub.0.6 
CuO.sub.2.22 with T.sub.c higher than 88 K. by firing mixtures of 4N 
Y.sub.2 O.sub.3, 3N BaCO.sub.3 and 3N CuO in the desired proportions. The 
mixtures were prefired at 1000.degree. C. for 5 hours. They were ground, 
pelletized and sintered at 900.degree. C. for 15 hours in air and cooled 
to room temperature in the furnace. They also disclose that almost 
equivalent results were also obtained by starting from concentrated 
nitrate solution of 4N Y.sub.2 O.sub.3, GR grade Ba(NO.sub.3).sub.2 and 
Cu(NO.sub.3).sub.2. 
Takayama-Muromachi et al., Jpn. J. Appl. Phys. 26, L476-L478 (1987), 
disclose the preparation of a series of samples to try to identify the 
superconducting phase in the Y-Ba-Cu-O system. Appropriate amounts of 
Y.sub.2 O.sub.3, BaCO.sub.3 and CuO were mixed in an agate mortar and then 
fired at 1173.+-.2 K. for 48-72 hours with intermediate grindings. X-ray 
diffraction powder patterns were obtained. The suggested composition of 
the superconducting compound in Y.sub.1-x Ba.sub.x CuO.sub.y where 
0.6&lt;.times.&lt;0.7. 
Hosoya et al., Jpn. J. Appl. Phys. 26, L456-L457 (1987), disclose the 
preparation of various superconductor compositions in the L-Ba-Cu-O 
systems where L=Tm, Er, Ho, Dy, Eu and Lu. Mixtures of the proper amounts 
of the lanthanide oxide (99.9% pure), CuO and BaCO.sub.3 were heated in 
air. The obtained powder specimens were reground, pressed into pellets and 
heated again. 
Hirabayashi et al., Jpn. J. Appl. Phys. 26, L454-L455 (1987), disclose the 
preparation of superconductor samples of nominal composition Y.sub.1/3 
Ba.sub.2/3 CuO.sub.3-x by coprecipitation from aqueous nitrate solution. 
Oxalic acid was used as the precipitant and insoluble Ba, Y and Cu 
compounds were formed at a constant pH of 6.8. The decomposition of the 
precipitate and the solid-state reaction were performed by firing in air 
at 900.degree. C. for 2 hours. The fired products were pulverized, 
cold-pressed into pellets and then sintered in air at 900.degree. C. for 5 
hours. The authors found that the sample was of nearly single phase having 
the formula Y.sub.1 Ba.sub.2 Cu.sub.3 O.sub.7. The diffraction pattern was 
obtained and indexed as having tetragonal symmetry. 
Ekino et al., Jpn. J. Appl. Phys. 26, L452-L453 (1987), disclose the 
preparation of a superconductor sample with nominal composition Y.sub.1.1 
Ba.sub.0.9 CuO.sub.4-y. A prescribed amount of powders of Y.sub.2 O.sub.3, 
BaCO.sub.3 and CuO was mixed for about an hour, pressed under 6.4 
ton/cm.sup.2 (14 MPa) into pellet shape and sintered at 1000.degree. C. in 
air for 3 hours. 
Akimitsu et al., Jpn. J. Appl. Phys. 26, L449-L451 (1987), disclose the 
preparation of samples with nominal compositions represented by (Y.sub.1-x 
Ba.sub.x).sub.2 CuO.sub.4-y. The specimens were prepared by mixing the 
appropriate amounts of powders of Y.sub.2 O.sub.3, BaCO.sub.3 and CuO. The 
resulting mixture was pressed and heated in air at 1000.degree. C. for 3 
hours. Some samples were annealed at appropriate temperatures in O.sub.2 
or CO.sub.2 for several hours. The authors noted that there seemed to be a 
tendency that samples annealed in O.sub.2 showed a superconducting 
transition with a higher onset temperature but a broader transition than 
non-annealed samples. 
Semba et al., Jpn. J. Appl. Phys. 26, L429-L431 (1987), disclose the 
preparation of samples of Y.sub.x Ba.sub.1-x CuO.sub.4-d where x=0.4 and 
x=0.5 by the solid state reaction of BaCO.sub.3, Y.sub.2 O.sub.3 and CuO. 
The mixtures are heated to 950.degree. C. for several hours, pulverized, 
and then pressed into disk shape. This is followed by the final heat 
treatment at 1100.degree. C. in one atmosphere O.sub.2 gas for 5 hours. 
The authors identified the phase that exhibited superconductivity above 90 
K. as one that was black with the atomic ratio of Y:Ba:Cu of 1:2:3. The 
diffraction pattern was obtained and indexed as having tetragonal 
symmetry. 
Hatano et al., Jpn. J. Appl. Phys. 26, L374-L376 (1987), disclose the 
preparation of the superconductor compound Ba.sub.0.7 Y.sub.0.3 Cu.sub.1 
O.sub.x from the appropriate mixture of BaCO.sub.3 (purity 99.9%), Y.sub.2 
O.sub.3 (99.99%) and CuO (99.9%). The mixture was calcined in an alumina 
boat heated at 1000.degree. C. for 10 hours in a flowing oxygen 
atmosphere. The color of the resulting well-sintered block was black. 
Hikami et al., Jpn. J. Appl. Phys. 26, L347-L348 (1987), disclose the 
preparation of a Ho-Ba-Cu oxide, exhibiting the onset of superconductivity 
at 93 K. and the resistance vanishing below 76 K., by heating a mixture of 
powders Ho.sub.2 O.sub.3, BaCO.sub.3 and CuO with the composition 
Ho:Ba:Cu=0.246:0.336:1 at 850.degree. C. in air for two hours. The sample 
was then pressed into a rectangular shape and sintered at 800.degree. C. 
for one hour. The sample looked black, but a small part was green. 
Matsushita et al., Jpn. J. Appl. Phys. 26, L332-L333 (1987), disclose the 
preparation of Ba.sub.0.5 Y.sub.0.5 Cu.sub.1 O.sub.x by mixing appropriate 
amounts of BaCO.sub.3 (purity 99.9%), Y.sub.2 O.sub.3 (99.99%) and CuO 
(99.9%). The mixture was calcined at 1000.degree. C. for 11 hours in a 
flowing oxygen atmosphere. The resultant mixture was then pulverized and 
cold-pressed into disks. The disks were sintered at 900.degree. C. for 4 
hours in the same oxygen atmosphere. The calcined powder and disks were 
black. A superconducting onset temperature of 100 K. was observed. 
Maeno et al., Jpn. J. Appl. Phys. 26, L329-L331 (1987), disclose the 
preparation of various Y-Ba-Cu oxides by mixing powders of Y.sub.2 
O.sub.3, BaCO.sub.3 and CuO, all 99.99% pure, with a pestle and mortar. 
The powders were pressed at 100 kgf/cm.sup.2 (98.times.10.sup.4 Pa) for 
10-15 minutes to form pellets with a diameter of 12 mm. The pellets were 
black. The heat treatment was performed in two steps in air. First, the 
pellets were heated in a horizontal, tubular furnace at 800.degree. C. for 
12 hours before the heater was turned off to cool the pellets in the 
furnace. The pellets were taken out of the furnace at about 200.degree. C. 
About half the samples around the center of the furnace turned green in 
color, while others away from the center remained black. The strong 
correlation with location suggested to the authors that this reaction 
occurs critically at about 800.degree. C. The pellets were then heated at 
1200.degree. C. for 3 hours and then allowed to cool. Pellets which turned 
light green during the first heat treatment became very hard solids 
whereas pellets which remained black in the first heat treatment slightly 
melted or melted down. Three of the samples exhibited an onset of 
superconductivity above 90 K. 
Iguchi et al., Jpn. J. Appl. Phys. 26, L327-L328 (1987), disclose the 
preparation of superconducting Y.sub.0.8 Ba.sub.1.2 CuO.sub.y by sintering 
a stoichiometrical mixture of Y.sub.2 O.sub.3, BaCO.sub.3 and CuO at 
900.degree. C. and at 1000.degree. C. in air. 
Hosoya et al., Jpn. J. Appl. Phys. 26, L325-L326 (1987), disclose the 
preparation of various superconducting specimens of the L-M-Cu-O systems 
where L=Yb, Lu, Y, La, Ho and Dy and M=Ba and a mixture of Ba and Sr by 
heating the mixtures of appropriate amounts of the oxides of the rare 
earth elements (99.9% pure), CuO, SrCO.sub.3 and/or BaCO.sub.3 in air at 
about 900.degree. C. Green powder was obtained. The powder samples were 
pressed to form pellets which were heated in air until the color became 
black. 
Takagi et al., Jpn. J. Appl. Phys. 26, L320-L321 (1987), disclose the 
preparation of various Y-Ba-Cu oxides by reacting mixtures containing the 
prescribed amounts of powders of Y.sub.2 O.sub.3, BaCO.sub.3 and CuO at 
1000.degree. C., remixing and heat-treating at 1100.degree. C. for a few 
to several hours. An onset temperature of superconductivity at 95 K. or 
higher was observed for a specimen with the nominal composition of 
(Y.sub.0.9 Ba.sub.0.1)CuO.sub.y. 
Hikami et al., Jpn. J. Appl. Phys. 26, L314-L315 (1987), disclose the 
preparation of compositions in the Y-Ba-Cu-O system by heating the powders 
of Y.sub.2 O.sub.3, BaCO.sub.3 and CuO to 800.degree. C. or 900.degree. C. 
in air for 2-4 hours, pressing into pellets at 4 kbars (4.times.10.sup.5 
Pa) and reheating to 800.degree. C. in air for 2 hours for sintering. The 
samples show an onset of superconductivity at 85 K. and a vanishing 
resistance at 45 K. 
Bourne et al., Phys. Letters A 120, 494-496 (1987), disclose the 
preparation of Y-Ba-Cu-O samples of Y.sub.2-x Ba.sub.x CuO.sub.4 by 
pressing finely ground powders of Y.sub.2 O.sub.3, BaCO.sub.3 and CuO into 
pellets and sintering the pellets in an oxygen atmosphere at 1082.degree. 
C. Superconductivity for samples having x equal to about 0.8 was reported. 
Moodenbaugh et al., Phys. Rev. Lett. 58, 1885-1887 (1987), disclose 
superconductivity near 90 K. in multiphase samples with nominal 
composition Lu.sub.1.8 Ba.sub.0.2 CuO.sub.4 prepared from dried Lu.sub.2 
O.sub.3, high-purity BaCP.sub.3 (BaCO.sub.3 presumably), and fully 
oxidized CuO. These powders were ground together in an agate mortar and 
then fired overnight in air at 1000.degree. C. in Pt crucibles. This 
material was ground again, pelletized, and then fired at 1100.degree. C. 
in air for 4-12 hours in Pt crucibles. Additional samples fired solely at 
1000.degree. C. and those fired at 1200.degree. C. show no signs of 
superconductivity. 
Hor et al., Phys. Rev. Lett. 58, 1891-1894 (1987), disclose 
superconductivity in the 90 K. range in ABa.sub.2 Cu.sub.3 O.sub.6+x with 
A=La, Nd, Sm, Eu, Gd, Ho, Er, and Lu in addition to Y. The samples were 
synthesized by the solid-state reaction of appropriate amounts of 
sesquioxides of La, Nd, Sm, Eu, Gd, Ho, Er, and Lu, BaCO.sub.3 and CuO in 
a manner similar to that described in Chu et al., Phys. Rev. Lett. 58, 405 
(1987) and Chu et al., Science 235, 567 (1987). 
Morgan, "Processing of Crystalline Ceramics", Palmoor et al., eds., Plenum 
Press, New York, 67-76 (1978), in discussing chemical processing for 
ceramics states that where direct synthesis is not immediately achieved, 
the use of co-precipitation, even if not completely homogeneous on a 
molecular scale is so vastly superior for uniform powder preparation to 
the use of ball milled oxides, that it should be the method of choice. He 
further discusses conditions for preparing perovskites or potassium nickel 
fluoride type structures using the oxides of Ca, Sr, Li, lanthanides, etc. 
and hot solutions of transition metal nitrates and acetates. 
C. Michel et al., Z. Phys. B - Condensed Matter 68, 421 (1987), disclose a 
novel family of superconducting oxides in the Bi-Sr-Cu-O system with 
composition close to Bi.sub.2 Sr.sub.2 Cu.sub.2 O.sub.7+.delta.. A pure 
phase was isolated for the composition Bi.sub.2 Sr.sub.2 Cu.sub.2 
O.sub.7+.delta.. The X-ray diffraction pattern for this material exhibits 
some similarity with that of perovskite and the electron diffraction 
pattern shows the perovskite subcell with the orthorhombic cell parameters 
of a=5.32 A (0.532 nm), b=26.6 A (2.66 nm) and c=48.8 A (4.88 nm). The 
material made from ultrapure oxides has a superconducting transition with 
a midpoint of 22 K. as determined from resistivity measurements and zero 
resistance below 14 K. The material made from commercial grade oxides has 
a superconducting transition with a midpoint of 7 K. In each case a 
mixture of Bi.sub.2 O.sub.3, CuO and SrCO.sub.3 was heated at 800.degree. 
C. for 12 hours in air, sintered at 900.degree. C. for 2 hours in air and 
quenched to room temperature. 
Akimitsu et al., Jpn. J. Appl. Phys. 26, L2080 (1987) disclose a Bi-Sr-Cu-O 
composition with a superconducting onset temperature of near 8 K. made by 
firing well-dried mixtures of Bi.sub.2 O.sub.3, SrCO.sub.3 and CuO powders 
at about 880.degree. C. in air for 12 hours. 
H. Maeda et al., Jpn. J. Appl. Phys. 27, L209 (1988), disclose a 
superconducting oxide in the Bi-Sr-Ca-Cu-O system with the composition 
near BiSrCaCu.sub.2 Ox and a superconducting transition temperature 
T.sub.c of about 105 K. The samples were prepared by calcining a mixture 
of Bi.sub.2 O.sub.3, SrCO.sub.3, CaCO.sub.3, and CuO powders at 
800.degree.-870.degree. C. for 5 hours. The material was reground, 
cold-pressed into pellets at a pressure of 2 ton/cm.sup.2, sintered at 
about 870.degree. C. in air or oxygen and furnace-cooled to room 
temperature. 
The commonly assigned application, "Superconducting Metal Oxide 
Compositions and Process For Making Them", Ser. No. 153,107, filed Feb. 8, 
1988, a continuation-in-part of Ser. No. 152,186, filed Feb. 4, 1988, 
disclose superconducting compositions having the nominal formula Bi.sub.a 
Sr.sub.b Ca.sub.c Cu.sub.3 O.sub.x wherein a is from about 1 to about 3, b 
is from about 3/8 to about 4, c is from about 3/16 to about 2 and x=(1.5 
a+b+c+y) where y is from about 2 to about 5, with the proviso that b+ c is 
from about 3/2 to about 5, said compositions having superconducting 
transition temperatures of about 70 K. or higher. It also discloses the 
superconducting metal oxide phase having the formula Bi.sub.2 Sr.sub.3-z 
Ca.sub.z Cu.sub.2 O.sub.8+w wherein z is from about 0.1 to about 0.9, 
preferably 0.4 to 0.8 and w is greater than zero but less than about 1. M. 
A. Subramanian et al., Science 239, 1015 (1988) also disclose the Bi.sub.2 
Sr.sub.3-z Ca.sub.z Cu.sub.2 O.sub.8+w superconductor and a method for 
preparing it. Single crystals were grown from a mixture of Bi.sub.2 
O.sub.3, CaCO.sub.3, SrO.sub.2 /Sr(NO.sub.3).sub.2 and CuO in proportions 
such that the atomic ratio Bi:Sr:Ca:Cu=2:2:1:3. The mixture was heated to 
850.degree. to 900.degree. C., held for 36 hours and cooled at the rate of 
1.degree. C. per minute. 
L. F. Schneemeyer et al., Nature 332, 422 (1988), disclose an alkali 
chloride flux method to grow superconducting single crystals in the 
Bi-Sr-Ca-Cu-O system. Pre-reacted Bi-Sr-Ca-Cu-O mixtures were prepared 
from high-purity Bi.sub.2 O.sub.3, SrCO.sub.3, Ca(OH).sub.2, and CuO by 
slowly heating to 800.degree.-850.degree. C. with intermediate grinding 
steps. Charges consisting of 10-50 wt % Bi-Sr-Ca-Cu-O mixtures thoroughly 
mixed with NaCl, KCl or other alkali halide salt or salt mixtures were 
placed in crucibles, heated above the melting temperature if the salt or 
salt mixture, and cooled at rates of 1.degree.-10.degree. C. per hour. 
S. Kondoh et al., Solid State Comm. 65, 1329 (1988), disclose a 
superconductor composition in the Tl-Ba-Cu-O system with an onset of 
superconductivity as high as 20 K. These superconductors were prepared by 
heating a mixture of Tl.sub.2 O.sub.3, BaO and CuO at about 650.degree. C. 
for 12 hours. The producy was reground, pressed into pellets and heated 
again at 700.degree. C. for about 20 hours. 
Z. Z. Sheng et al., Nature 332, 55 (1988) and Z. Z. Sheng et al., Phys. 
Rev. Lett. 60, 937 (1988) disclose superconductivity in the Tl-Ba-Cu-O 
system. These samples are reported to have onset temperatures above 90 K. 
and zero resistance at 81 K. The samples were prepared by mixing and 
grinding appropriate amounts of BaCO.sub.3 and CuO with an agate mortar 
and pestle. This mixture was heated in air at 925.degree. C. for more than 
24 hours with several intermediate grindings to obtain a uniform black 
oxide Ba-Cu oxide powder which was mixed with an appropriate amount of 
Tl.sub.2 O.sub.3, completely ground and pressed into a pellet with a 
diameter of 7 mm and a thickness of 1-2 mm. The pellet was then put into a 
tube furnace which had been heated to 880.degree.-910.degree. C. and was 
heated for 2-5 minutes in flowing oxygen. As soon as it had slightly 
melted, the sample was taken from the furnace and quenched in air to room 
temperature. It was noted by visual inspection that Tl.sub.2 O.sub.3 had 
partially volatilized as black smoke, part had become a light yellow 
liquid, and part had reacted with Ba-Cu oxide forming a black, partially 
melted, porous material. 
Z. Z. Sheng et al., Nature 332, 138 (1988) disclose superconductivity in 
the Tl-Ba-Ca-Cu-O system. Samples are reported to have onset temperatures 
at 120 K. and zero resistance above 100 K. The samples were prepared by 
mixing and grinding appropriate amounts of Tl.sub.2 O.sub.3, CaO and 
BaCuO.sub.4. This mixture was pressed into a pellet with a diameter of 7 
mm and a thickness of 1-2 mm. The pellet was then put into a tube furnace 
which had been heated to 880.degree.-910.degree. C. and was heated for 3-5 
minutes in flowing oxygen. The sample was then taken from the furnace and 
quenched in air to room temperature. 
R. M. Hazen et al., Phy. Rev. Lett. 60, 1657 (1988), disclose two 
superconducting phases in the Tl-Ba-Ca-Cu-O system, Tl.sub.2 Ba.sub.2 
Ca.sub.2 Cu.sub.3 O.sub.10 and Tl.sub.2 Ba.sub.2 CaCu.sub.2 O.sub.8 and 
the method of preparation. Appropriate amounts of Tl.sub.2 O.sub.3, CaO, 
and BaCu.sub.3 O.sub.4 or Ba.sub.2 Cu.sub.3 O.sub.4 were completely mixed, 
ground and pressed into a pellet. A quartz boat containing the pellet was 
placed in a tube furnace which had been preheated to 
880.degree.-910.degree. C. The sample was heated for 3 to 5 minutes in 
flowing oxygen and the furnace cooled to room temperature in 1 to 1.5 
hours. 
Subramanian et al., Nature 332, 420 (1988) disclose the preparation of 
superconducting phases in the Tl-Ba-Ca-Cu-O system by reacting Tl.sub.2 
O.sub.3, CaO.sub.2 or CaCO.sub.3, BaO.sub.2 and CuO at 
850.degree.-910.degree. C. in air or in sealed gold tubes for 15 minutes 
to 3 hours. 
SUMMARY OF THE INVENTION 
The present invention provides an improved process for preparing a 
precursor to a copper oxide-containing superconducting composition. The 
composition may be of a rare earth metal-, bismuth- or thallium-based 
alkaline earth metal-copper-oxide composition. The process for preparing 
the superconducting composition involves heating the precursor and in 
addition, in the case of the rare earth metal-based compositions, cooling 
the previously-heated precursor under prescribed conditions. The resulting 
superconducting powder can be pressed into a desired shape and then, under 
prescribed conditions, sintered, and for the rare earth metal-based 
compositions cooled, to provide a superconducting shaped article. This 
invention also includes providing the shaped articles prepared by the 
process of the invention. 
In its broadest sense, the invention involves preparing the precursor from 
an aqueous suspension by mixing an aqueous solution of a carboxylate e.g. 
an acetate or a nitrate of copper at a temperature of 
50.degree.-100.degree. C. with either (1) a hydroxide or an oxide or a 
peroxide of an alkaline earth metal, e.g. barium, calcium or strontium and 
bismuth oxide (Bi.sub.2 O.sub.3) or thallium oxide (Tl.sub.2 O.sub.3) or a 
rare earth oxide, e.g. Y.sub.2 O.sub.3, or (2) a hydroxide of the alkaline 
earth metal and a carboxylate or a nitrate of bismuth, thallium or the 
rare earth. The relative quantities of the compounds are selected to 
provide the atomic ratios of M (Bi, Tl or rare earth) -to- A (alkaline 
earth metal) -to- copper -to- oxygen that are known to provide 
superconducting compositions, e.g. M(rare earth)Ba.sub.2 Cu.sub.3 O.sub.x 
where x is 6.5-7.0, Bi.sub.2 Sr.sub.2 CuO.sub.x where x is 6-6.5, Bi.sub.2 
Sr.sub.2 CaCu.sub.2 O.sub.x where x is 8-9, Tl.sub.2 BA.sub. 2 CuO.sub.x 
where x is 6-6.5, Tl.sub.2 Ba.sub.2 CaO.sub.x where x is 8-9, Tl.sub.2 
Ba.sub.2 Cu.sub.2 Cu.sub.3 O.sub.x where x is 10-11.5. 
Thus, the invention as it relates to the rare earth metal-containing 
superconducting compositions involves a process for preparing a 
superconducting composition having the formula MBa.sub.2 Cu.sub.3 O.sub.x 
wherein M is selected from the group consisting of Y, Nd, Sm, Eu, Gd, Dy, 
Ho, Er, Tm, Yb and Lu; x is from about 6.5 to about 7.0; said composition 
having a superconducting transition temperature of about 90 K.; said 
process consisting essentially of (a) mixing Ba(OH).sub.2.8H.sub.2 O, BaO 
or BaO.sub.2 and M.sub.2 O.sub.3 with an aqueous solution of cupric 
carboxylate or cupric nitrate at a temperature from about 50.degree. C. to 
about 100.degree. C., or mixing Ba(OH).sub.2.8H.sub.2 O with an aqueous 
solution of Cu and M carboxylates or nitrates at a temperature from about 
50.degree. C. to about 100.degree. C., to obtain a suspension having 
M:Ba:Cu present in an atomic ratio of about 1:2:3; 
(b) drying the suspension formed in step (a) to obtain a powder precursor; 
(c) heating said precursor in an oxygen-containing atmosphere at a 
temperature from about 850.degree. C. to about 950.degree. C. for a time 
sufficient to form MBa.sub.2 Cu.sub.3 O.sub.y, where y is from about 6.0 
to about 6.4; and 
(d) maintaining the MBa.sub.2 Cu.sub.3 O.sub.y in an oxygen-containing 
atmosphere while cooling for a time sufficient to obtain the desired 
product. The MBa.sub.2 Cu.sub.3 O.sub.x powder can be pressed into a 
desired shape and then, under prescribed conditions sintered and cooled to 
provide a MBa.sub.2 Cu.sub.3 O.sub.x shaped article. 
The invention provides an improved process for preparing a superconducting 
composition of bismuth-based alkaline earth metal-copper-oxide wherein 
the alkaline earth metal is Sr or both Sr and Ca; 
the process consisting essentially of 
(a) mixing Sr(OH).sub.2.8H.sub.2 O, SrO or SrO.sub.2 and, if both Sr and Ca 
are to be present, Ca(OH).sub.2, CaO or CaO.sub.2 and Bi.sub.2 O.sub.3 
with an aqueous solution of cupric carboxylate or cupric nitrate at a 
temperature from about 50.degree. C. to about 100.degree. C. to obtain a 
suspension having Bi:Sr:Ca:Cu present in the desired atomic ratio; 
(b) drying the suspension formed in step (a) to obtain a powder precursor; 
and 
(c) heating said precursor in an oxygen-containing atmosphere at a 
temperature from about 850.degree. C. to about 875.degree. C. for a time 
sufficient to form the superconducting oxide. 
Preferred is the process in which Bi:Sr:Ca:Cu are in the atomic ratios 
2:2:0:1 or 2:2:1:2 and the respective superconducting oxide has the 
nominal formula Bi.sub.2 Sr.sub.2 CuO where x is from about 6 to about 6.5 
or the nominal formula Bi.sub.2 Sr.sub.2 CaCu.sub.2 O.sub.x, where x is 
from about 8 to about 9, both with orthorhombic symmetry. 
The invention also provides an improved process for preparing a 
superconducting composition of thallium-based alkaline earth 
metal-copper-oxide wherein 
the alkaline earth metal is Ba or both Ba and Ca; 
the process consisting essentially of 
(a) mixing Ba(OH).sub.2.8H.sub.2 O, BaO or BaO.sub.2 and, if both Ba and Ca 
are to be present, Ca(OH).sub.2, CaO or CaO.sub.2 and Tl.sub.2 O.sub.3 
with an aqueous solution of cupric carboxylate or cupric nitrate at a 
temperature from about 50.degree. C. to about 100.degree. C., or mixing 
Ba(OH).sub.2.8H.sub.2 O and, if both Ba and Ca are to be present, 
Ca(OH).sub.2 with an aqueous solution of Cu and Tl carboxylates or 
nitrates at a temperature from about 50.degree. C. to about 100.degree. 
C., to obtain a suspension having Tl:Ba:Ca:Cu present in the desired 
atomic ratio; 
(b) drying the suspension formed in step (a) to obtain a powder precursor; 
and 
(c) heating said precursor in an oxygen-containing atmosphere at a 
temperature from about 850.degree. C. to about 920.degree. C. for a time 
sufficient to form the superconducting oxide. 
Preferred is the process in which Tl:Ba:Ca:Cu are in the atomic ratios 
2:2:0:1, 2:2:1:2 or 2:2:2:3 and the respective superconducting oxide has 
the nominal formula Tl.sub.2 Ba.sub.2 CuO.sub.x where x is from about 6 to 
about 6.5, the nominal formula Tl.sub.2 Ba.sub.2 CaCu.sub.2 O.sub.x where 
x is from about 8 to about 9 or the nominal formula Tl.sub.2 Ba.sub.2 
Ca.sub.2 Cu.sub.3 O.sub.x where x is from about 10 to about 11.5, all with 
tetragonal symmetry.

DETAILED DESCRIPTION OF THE INVENTION 
The various products of the process of this invention is a nearly 
single-phase superconducting oxide. No additional grinding, annealing or 
refining is necessary to produce the superconducting oxide composition. 
The use of a suspension to form a very finely divided precursor powder 
assures a high degree of homogeneity of the reactant cations relative to 
conventional solid state techniques and results in the preparation of a 
uniform, nearly single-phase superconducting oxide composition by a 
process in which this precursor is heated in air or oxygen. 
In the process, a suspension is prepared which is then used to generate a 
precursor powder for later heating. The suspension is prepared by using, 
as the source of the alkaline earth metal, the alkaline earth metal 
hydroxide, the alkaline earth metal peroxide or the alkaline earth metal 
oxide. Preferably, the alkaline earth metal hydroxide is used. To 
facilitate mixing, particularly when preparing large size batches, the 
alkaline earth metal hydroxide can be added as an aqueous solution. If the 
alkaline earth metal peroxide is used, it should be added slowly to the 
solution of the copper compound because of the evolution of oxygen. The 
copper compound used in preparing the suspension is an aqueous, preferably 
concentrated, solution of cupric carboxylate or cupric nitrate. 
Preferably, the source of copper is cupric carboxylate. Suitable 
carboxylates include the formate, acetate, and other water soluble 
carboxylates, but the acetate is preferred. 
In one embodiment of the invention, the suspension is prepared by mixing 
either M.sub.2 O.sub.3 as a source of the rare earth metal, Bi.sub.2 
O.sub.3 as a source of bismuth, or Tl.sub.2 O.sub.3 as a source of 
thallium and the alkaline earth metal compound with an aqueous solution of 
cupric carboxylate or cupric nitrate at a temperature from about 
50.degree. C. to about 100.degree. C. Preferably, the rare earth metal, 
bismuth or thallium compound and the alkaline earth metal compound are 
mixed together prior to addition to the aqueous solution. 
In another embodiment of the invention, the suspension is prepared by 
mixing the alkaline earth metal compound with an aqueous solution of 
copper carboxylate, nitrate or a mixture thereof and either a rare earth 
metal or a thallium carboxylate, nitrate or a mixture thereof at a 
temperature from about 50.degree. C. to about 100.degree. C. In this 
embodiment, first as in the previous embodiment, the preferred source of 
copper is a cupric carboxylate and of these the acetate is preferred. 
Preferably, the source of the rare earth metal is a rare earth metal 
carboxylate. Suitable carboxylates include the acetate and other water 
soluble carboxylates, but the acetate is preferred. This latter embodiment 
of the invention can also be used to prepare the bismuth-based oxide. 
However, the low solubilities of the bismuth salts such as bismuth 
nitrate, bismuth acetate and the other bismuth carboxylates offer no 
significant advantage regarding homogeneity of the suspension formed over 
that obtained by using Bi.sub.2 O.sub.3 as in the previous embodiment. 
In either embodiment, the concentration of the aqueous solution is below 
saturation, and heating can be effected before, during or after the solids 
are added. 
The resulting suspension is then dried to remove the solvent and form the 
powder precursor. Drying can be effected by conventional techniques. For 
instance, drying can be accomplished by continued heating of the 
suspension at a temperature from about 50.degree. C. to about 100.degree. 
C. while the suspension is stirred. As the solvent is removed from the 
suspension, the viscosity of the suspension increases until a thick paste 
is formed. This paste is further heated at a temperature from about 
100.degree. C. to about 200.degree. C. to produce the precursor solid 
which is then gently milled to form a powder precursor. Alternatively, the 
suspension can be spray-dried or freeze-dried using conventional 
techniques to produce a powder precursor without milling. 
The powder precursor can be heated in an oxygen-containing atmosphere at a 
temperature appropriate for the specific metal-based oxide, where for the 
rare earth metal-based oxide the temperature is from about 850.degree. C. 
to about 950.degree. C., for the bismuth-based oxide the temperature is 
from about 850.degree. C. to about 875.degree. C., and for the 
thallium-based oxide the temperature is from about 850.degree. C. to about 
920.degree. C., for a time sufficient to form the superconducting oxide 
except in the case of the rare earth metal-based oxide where the product 
formed is during the heating is maintained in an oxygen-containing 
atmosphere while cooling for a time sufficient to form the superconducting 
oxide. For heating, the powder precursor is placed in a non-reactive 
container, e.g., an alumina or gold crucible or tray. 
The superconducting product powder can be pressed into a desired shape and 
then sintered in an oxygen-containing atmosphere at a temperature as 
indicated above for the preparation of the specific metal-based oxide, 
i.e., for the rare earth metal-based oxide the temperature is from about 
850.degree. C. to about 950.degree. C., for the bismuth-based oxide the 
temperature is from about 850.degree. C. to about 875.degree. C., and for 
the thallium-based oxide the temperature is from about 850.degree. C. to 
about 920.degree. C., with the proviso that in the case of the rare earth 
metal-based oxide the shaped article is maintained in an oxygen-containing 
atmosphere while cooling. 
The process of this invention provides a method for preparing a 
superconducting composition that requires no special atmosphere during the 
heating step, no subsequent grinding, reheating or annealing, no extended 
heating times and no refining of the product to separate the desired 
superconducting composition from other phases. 
The product of the process of the invention involving the use of the rare 
earth metal is essentially a single-phase, superconducting compound with 
orthorhombic symmetry. No additional grinding, annealing or refiring is 
necessary to produce the MBa.sub.2 Cu.sub.3 O.sub.x composition. The 
process of the invention is an improved process for preparing 
superconducting compositions having the formula MBa.sub.2 Cu.sub.3 
O.sub.x, M being selected from the group consisting of Y, Nd, Sm, Eu, Gd, 
Dy, Ho, Er, Tm, Yb and Lu, preferably Y. The parameter x is from about 6.5 
to about 7.0, but is preferably from about 6.8 to 7.0. The use of a 
suspension to form a precursor powder assures a high degree of mixing of 
the starting materials relative to conventional solid state techniques and 
results in the preparation of a uniform, practically single-phase 
superconducting MBa.sub.2 Cu.sub.3 O.sub.x composition by a process in 
which this precusor is heated in air at a temperature of about 850.degree. 
C. to about 950.degree. C. 
In the process of the invention a suspension is prepared which is then used 
to generate a precursor powder for later heating. The suspension is 
prepared by using, as the source of barium, Ba(OH).sub.2.8H.sub.2 O, 
BaO.sub.2 or BaO. Preferably, Ba(OH).sub.2.8H.sub.2 O is used. If 
BaO.sub.2 is used, it should be added slowly to the Cu solution because of 
the evolution of oxygen. The second component used in preparing the 
suspension is an aqueous, preferably concentrated, solution of cupric 
carboxylate or cupric nitrate. Preferably, the source of copper is cupric 
carboxylate. Suitable carboxylates include the formate, acetate, and other 
water soluble cupric carboxylates, but the acetate is preferred. In one 
embodiment of the invention, the suspension is prepared by mixing M.sub.2 
O.sub.3 and the barium compound with an aqueous solution of cupric 
carboxylate or cupric nitrate at a temperature from about 50.degree. C. to 
about 100.degree. C. Preferably, the M.sub.2 O.sub.3 and barium compound 
are mixed together prior to addition to the aqueous solution. In another 
embodiment of the invention, the suspension is prepared by mixing the 
barium compound with an aqueous solution of Cu carboxylate, nitrate or a 
mixture thereof and M carboxylate, nitrate or a mixture thereof at a 
temperature from about 50.degree. C. to about 100.degree. C. In this 
embodiment the preferred Cu source is the same as for the other 
embodiment. Preferably, the rare earth metal source is an M carboxylate. 
Suitable carboxylates include the acetate, and other water-soluble 
carboxylates, but the acetate is preferred. In either embodiment, the 
concentration of the aqueous solution is below saturation, and heating of 
the aqueous solution can be effected before, during or after the solids 
are added. The relative amounts of the sources of M, Ba and Cu used in 
forming the suspension from which the precursor is prepared are chosen 
such that the atomic ratio of M:Ba:Cu is about 1:2:3. Preferably, the 
starting materials used in the process of the invention are of relatively 
high purity, e.g., 99.9% by weight for copper acetate, 99.99% by weight 
for copper nitrate, &gt;98% by weight for Ba(OH).sub.2.8H.sub.2 O, 99.5% by 
weight for BaO.sub.2 and 99.9% by weight for M.sub.2 O.sub.3. Less pure 
starting materials can be used; however, the product may then contain an 
amount of another phase material comparable to the amount of impurity in 
the starting materials. It is particularly important to avoid the presence 
of impurities containing iron and other transition, but non-rare earth, 
metals in the reactants. The resulting suspension is then dried to remove 
the solvent and form the powder precursor. Drying can be effected by 
conventional techniques. For instance, drying can be accomplished by 
continued heating of the suspension at a temperature from about 50.degree. 
C. to about 100.degree. C. while the suspension is stirred. As the solvent 
is removed from the suspension, the viscosity of the suspension increases 
until a thick paste is formed. This thick paste is further heated at a 
temperature from about 100.degree. C. to 200.degree. C. to produce the 
precursor solid which is then gently milled to form a powder precursor. 
Alternatively, the suspension can be spray dried or freeze-dried using 
conventional techniques to produce a powder precursor without milling. The 
powder precursor is then heated in an oxygen-containing atmosphere at a 
temperature from about 850.degree. C. to about 950.degree. C., preferably 
from about 875.degree. C. to about 900.degree. C., for a time sufficient 
to form MBa.sub.2 Cu.sub.3 O.sub.y, where y is from about 6.0 to about 
6.4. It has been determined by TGA that when the powder precursor is 
heated to 900.degree. C., y is from about 6.0 to about 6.4. For heating, 
the powder precursor is placed in a non-reactive container, e.g., an 
alumina or gold crucible or tray. The oxygen-containing atmosphere can be 
air or oxygen gas, but is preferably air. The container with the powder 
precursor is placed in a furnace and brought to a temperature of about 
850.degree. C. to about 950.degree. C. It is the total time that the 
powder precursor is at temperatures in this range that is important. For 
example, when a heating rate of 20.degree. C. per minute is used to raise 
the temperature of the furnace containing the sample from ambient 
temperature to a final heating temperature is 900.degree. C., 1/2 to 2 
hours at this temperature are sufficient to produce, after cooling as 
prescribed herein, practically single-phase superconducting MBa.sub.2 
Cu.sub.3 O.sub.x. Longer heating times can be used. At the end of the 
heating time, the furnace is turned off, and the resulting material is 
allowed to cool in the oxygen-containing atmosphere for a time sufficient 
to obtain the desired product. Preferably, the material is cooled to below 
about 100.degree. C. (a time interval of about 4-5 hours) before the 
sample container is removed from the furnace. During the cooling step, the 
oxygen content of the material increases to give the desired MBa.sub.2 
Cu.sub.3 O.sub.x product. The additional oxygen which enters into the 
crystalline lattice of the material during this cooling step to form the 
desired product does so by diffusion. The rate at which oxygen enters the 
lattice is determined by a complex function of time, temperature, oxygen 
content of the atmosphere, sample form, etc. Consequently, there are 
numerous combinations of these conditions that will result in the desired 
product. For example, the rate of oxygen uptake by the material at 
500.degree. C. in air is rapid, and the desired product can be obtained in 
less than an hour under these conditions when the sample is in the form of 
a loosely packed, fine particle powder. However, if the sample is in the 
form of larger particles, or densely packed powders, the times required to 
obtain the desired product at 500.degree. C. in air will increase. The 
MBa.sub.2 Cu.sub.3 O.sub.x powder can be pressed into a desired shape, 
sintered in an oxygen-containing atmosphere at a temperature from about 
900.degree. C. to about 950.degree. C., and maintained in the 
oxygen-containing atmosphere while cooling as prescribed above to obtain a 
MBa.sub.2 Cu.sub.3 O.sub.x shaped article. Well sintered, shaped articles 
will take longer to form the desired product while cooling than will more 
porous ones, and for larger, well sintered, shaped articles many hours may 
be required. A convenient procedure for obtaining the desired product when 
the material is in the form of a powder or a small shaped object is to 
turn off the furnace in which the heating was conducted and to allow the 
material to cool in the furnace to a temperature approaching ambient 
(about 22.degree. C.) which typically requires a few hours. In the 
examples, cooling in the furnace to below about 100.degree. C. was found 
to be sufficient. Increasing the partial pressure of oxygen in the 
atmosphere surrounding the sample during cooling increases the rate at 
which oxygen enters the lattice. If, in a particular experiment, the 
material is cooled in such a manner that the MBa.sub.2 Cu.sub.3 O.sub.x 
product is not obtained, the material can be heated to an intermediate 
temperature, such as 500.degree. C., between ambient temperature and the 
final temperature used in the heating step and held at this temperature 
for a sufficient time to obtain the desired product. 
The product formed is practically single-phase and has orthorhombic 
symmetry as determined by X-ray diffraction measurements. 
The process of this invention as it relates to the rare earth metal 
superconductor provides a method for preparing a superconducting MBa.sub.2 
Cu.sub.3 O.sub.x composition that does not require a special atmosphere 
during the heating step, subsequent grinding, reheating or annealing, 
extended heating times or refining of the product to separate the desired 
superconducting MBa.sub.2 Cu.sub.3 O.sub.x composition from other phases. 
As used herein the phrase "consisting essentially of" means that additional 
steps can be added to the process of the invention so long as such steps 
do not materially alter the basic and novel characteristics of the 
invention. The presence of superconductivity at any given temperature can 
be determined by the Meissner effect, i.e., the exclusion of magnetic flux 
by a sample when in the superconducting state. 
The invention is further illustrated by the following examples in which 
temperatures are in degrees Celsius unless otherwise indicated. The 
chemicals (with purity indicated) used in the following examples of the 
process of this invention were Ba(OH).sub.2.8H.sub.2 O--(&gt;98%) obtained 
from Morton Thiokol Inc. or Research Organic/Inorganic Chemical Corp., 
BaO.sub.2 --(99.5%) obtained from Atomergic Chemetals Corp., Cu(C.sub.2 
H.sub.3 O.sub.2).sub.2.H.sub.2 O--(99.9%) obtained from J. T. Baker 
Chemical Co., Cu(NO.sub.3).sub.2.6H.sub.2 O--(99.999%) obtained from 
Johnson and Matthey Chemicals Ltd., Y(C.sub.2 H.sub.3 
O.sub.2).sub.3.XH.sub.2 O (20.6% H.sub.2 O)--(99.9%) obtained from Morton 
Thiokol Inc., and Y.sub.2 O.sub.3 --(99.9%) obtained from Alfa Research 
Chemicals and Materials, Bi.sub.2 O.sub.3 --(99.8%) obtained from Alfa 
Research Chemicals and Materials, Sr(OH).sub.2.8H.sub.2 O--(Technical 
Grade) obtained from Alfa Research Chemicals and Materials, and 
Ca(OH).sub.2 --(&gt;96%) obtained from EM Science. 
EXAMPLE 1 
Cu(C.sub.2 H.sub.3 O.sub.2).sub.2.H.sub.2 O (14.37 g, 0.048 mole) was 
dissolved in 100 cc distilled water and the resulting solution was heated 
to about 75.degree.. Y(C.sub.2 H.sub.3 O.sub.2).XH.sub.2 O (8.04 g, 0.024 
mole) was dissolved in 25 cc distilled water and the resulting solution 
was heated to about 75.degree.. These two solutions were combined to give 
a mixed solution containing copper and yttrium acetates to which 15.14 g 
Ba(OH).sub.2.8H.sub.2 O was slowly added with stirring. The resulting 
reaction suspension slowly changed color from blue to greenish-black and 
finally to a blackish-brown. The suspension was kept stirred and heated at 
about 75.degree. until a paste was obtained. This paste was further heated 
until dry to obtain a solid which was placed in a vacuum oven at 
170.degree. for 1 hour. The solid was then converted to a dark brown 
powder by hand grinding in an agate mortar and pestle. The X-ray 
diffraction pattern of this precursor solid showed that it was 
predominantly amorphous with some very poorly crystalline CuO also evident 
in the x-ray diffraction pattern. The yield was 25.90 g. 
A 5.26 g portion of the above precursor was spread into a thin layer in an 
alumina tray and heated in air in a furnace from ambient temperature to a 
final heating temperature of 900.degree. at a rate of about 20.degree. per 
minute. The temperature was maintained at 900.degree. for 2 hours. The 
furnace was then turned off and allowed to cool to a temperature below 
100.degree. before the sample was removed. The resulting product was black 
and the yield was 3.14 g. An X-ray diffraction powder pattern of the 
product showed that it was YBa.sub.2 Cu.sub.3 O.sub.x. The indices of the 
observed reflections, the d-spacings and relative intensities are shown in 
Table I. These results indicate that the YBa.sub.2 Cu.sub.3 O.sub.x 
product has orthorhombic symmetry. A very slight trace amount of 
BaCuO.sub.2 is also evident in the pattern. 
Scanning electron micrographs of the powder revealed that it consisted of 
isotropic particles with dimensions ranging from about 0.2 .mu.m to about 
3 .mu.m, with relatively little agglomeration. 
Measurement of the Meissner effect showed the powder sample to have a 
T.sub.c, a superconducting transition temperature, onset of about 90 K. 
TABLE I 
______________________________________ 
X-ray diffraction data for YBa.sub.2 Cu.sub.3 O.sub.x 
hkl d(nm) Intensity* 
______________________________________ 
002 0.5786 vvw 
003 
0.3863 m 
100 
012 
0.3206 w 
102 
013 
103 0.2720 vs 
110 
111 0.2642 vw 
112 0.2460 w 
005 
0.2325 m 
104 
113 0.2225 m 
020 
0.1936 m 
006 
200 0.1905 m 
115 0.1770 w 
016 
023 
106 0.1732 w 
120 
203 
210 0.1711 vw 
121 
122 0.1660 vw 
123 
0.1579 ms 
116 
213 0.1567 m 
______________________________________ 
*Legend 
s--strong 
m--moderate 
w--weak 
v--very 
EXAMPLE 2 
A 1.08 g portion of the precursor powder prepared using a procedure very 
similar to that described in Example 1 was spread into a thin layer in an 
alumina tray and heated in air in a furnace from ambient temperature to a 
final heating temperature of 900.degree. at a rate of about 20.degree. per 
minute. The temperature was maintained at 900.degree. for 30 minutes. The 
furnace was turned off and allowed to cool below 100.degree. before the 
sample was removed. The product was black and the yield was 0.66 g. An 
X-ray diffraction powder pattern of the material showed that the product 
was orthorhombic YBa.sub.2 Cu.sub.3 O.sub.x. The results were very similar 
to those given in Table I. There were also slight traces of BaCuO.sub.2, 
Y.sub.2 Cu.sub.2 O.sub.5 and BaCO.sub.3. 
Scanning electron micrographs of the powder showed that it was very similar 
in morphology to that described in Example 1. Measurement of the Meissner 
effect showed the powder sample to have a T.sub.c onset of about 90 K. 
EXAMPLE 3 
Cu(C.sub.2 H.sub.3 O.sub.2).sub.2.H.sub.2 O (28.75 g, 0.144 mole) was 
dissolved in 200 cc distilled water. The resulting solution was then 
heated to about 75.degree.. Ba(OH).sub.2.8H.sub.2 O (30.28 g, 0.096 mole) 
and 5.40 g of Y.sub.2 O.sub.3 (0.024 mole) were then ground together, by 
hand, in an agate mortar with a pestle. The resulting solid mixture was 
then added to the heated copper acetate solution to obtain a suspension 
which was at first bright blue, but within 10 minutes had turned to dark 
greenish-black, and after another 10 minutes had turned a uniform black. 
The suspension was kept stirred and heated at about 75.degree. until a 
paste was obtained. This paste was further heated until dry and the 
resulting solid was placed in a vacuum oven at 170.degree. for 1 hour. The 
solid was then converted to a dark brown powder by hand grinding in an 
agate mortar using a pestle. The X-ray diffraction powder pattern of this 
precursor solid showed that the powder was amorphous with some poorly 
crystalline CuO and a small amount of a poorly crystalline unidentified 
phase also present. The yield was 46.51 g. 
A 21.2 g portion of this precursor powder was spread into a thin layer in 
an alumina tray and heated in air in a furnace from ambient temperature to 
a final heating temperature of 900.degree. at a rate of about 20.degree. 
per minute. The temperature was maintained at 900.degree. for 8 hours. The 
furnace was then turned off and allowed to cool to a temperature below 
100.degree. C. before the sample was removed. The product was black and 
the yield was 14.25 g. An X-ray diffraction powder pattern of the material 
showed that it was orthorhombic YBa.sub.2 Cu.sub.3 O.sub.x, and the 
results were very similar to those given in Table I. Trace amounts of 
BaCuO.sub.2 and Y.sub.2 Cu.sub.2 O.sub.5 are also evident in the pattern. 
Scanning electron micrographs of the powder showed that it was very similar 
in morphology to that described in Example 1. Measurement of the Meissner 
effect showed the powder sample to have a T.sub.c onset of about 90 K. 
EXAMPLE 4 
A 1.14 g of precursor powder made by a procedure very similar to that 
described in Example 3 was spread into a thin layer in an alumina tray and 
heated in air in a furnace from ambient temperature to a final heating 
temperature of 900.degree. at a rate of about 20.degree. per minute. The 
temperature was maintained at 900.degree. for 2 hours. The furnace was 
then turned off and allowed to cool to a temperature below 100.degree. C. 
before the sample was removed. The product was black. An X-ray diffraction 
powder pattern of the material showed that it was orthorhombic YBa.sub.2 
Cu.sub.3 O.sub.x, and the results were very similar to those given in 
Table I. Trace amounts of BaCuO.sub.2 and Y.sub.2 Cu.sub.2 O.sub.5 are 
also evident in the pattern. 
Measurement of the Meissner effect showed the powder sample to have a 
T.sub.c onset of about 90 K. 
EXAMPLE 5 
Cu(C.sub.2 H.sub.3 O.sub.2).sub.2.H.sub.2 O (14.37 g, 0.072 mole) was 
dissolved in 100 cc distilled water, and the resulting solution was heated 
to about 75.degree.. Y(C.sub.2 H.sub.3 O.sub.2).sub.3.XH.sub.2 O (8.04 g, 
0.024 mole) was dissolved in 25 cc distilled water, and the resulting 
solution was also heated to about 75.degree. . These two solutions were 
combined to give a mixed solution of copper and yttrium acetates to which 
15.14 g (0.048 mole) of Ba(OH).sub.2.8H.sub.2 O was slowly added with 
stirring. The resulting suspension slowly changed color from blue to 
greenish blue and finally to blackish-brown. The suspension was kept 
stirred and heated at about 75.degree. for a little less than one hour. 
The heated suspension was then sprayed through an air atomization nozzle 
into a covered beaker containing liquid nitrogen. The nozzle, manufactured 
by Spraying Systems Co., Wheaton, Ill., was Model 9265-1/4 J-LUC fitted 
with fluid cap #2850-LUC, liquid orifice diameter of 0.7 mm (0.028 in) and 
air cap #70-LUC. The nozzle was pressurized by 140 kPa (20 psi) of air. 
The resulting slurry of liquid nitrogen and finely divided frozen powder 
was then freeze dried. The powder obtained was medium grey and very 
fluffy. Its bulk density was 18 times lower than that of powder obtained 
by conventional evaporation of the solvent to dryness reflecting the 
extremely fine particle size and low degree of agglomeration in the 
freeze-dried powder. The yield was 23.9 g. An X-ray diffraction powder 
pattern of the material showed that the powder was almost totally 
amorphous with some very poorly crystalline CuO also present. 
A 1.05 g portion of this freeze-dried powder was spread in a thin layer in 
an alumina tray and heated in air in a furnace from ambient temperature to 
a final heating temperature of 900.degree. at a rate of about 20.degree. 
per minute. The temperature was maintained at 900.degree. for 2 hours. The 
furnace was turned off and allowed to cool below 100.degree. before the 
sample was removed. The resulting powder was black and the yield is 0.61 
g. An X-ray diffraction powder pattern of the material showed that the 
product was orthorhombic YBa.sub.2 Cu.sub.3 O.sub.x, and the results were 
very similar to those given in Table I. There were a minor impurity of 
Y.sub.2 Cu.sub.2 O.sub.5 and a trace amount of Y.sub.2 BaCuO.sub.5. 
Measurement of the Meissner effect showed the powder to have a T.sub.c 
onset of about 90 K. 
EXAMPLE 6 
Cu(C.sub.2 H.sub.3 O.sub.2).sub.2.H.sub.2 O (11.50 g, 0.058 mole) was 
dissolved in 80 cc of distilled water, and the resulting solution was 
heated to about 75.degree.. Y(C.sub.2 H.sub.3 O.sub.2).XH.sub.2 O (6.43 g, 
0.019 mole) was dissolved in 25 cc of distilled water, and the resulting 
solution was also heated to about 75.degree.. These two solutions were 
combined after which 12.11 g of Ba(OH).sub.2.8H.sub.2 O (0.038 mole) were 
slowly added with stirring. The resulting suspension turned from dark 
blue, to greenish black, to black, all within about 20 min. The suspension 
was kept stirred and heated at about 75.degree. for one hour. The heated 
suspension was then spray dried using a Buchi laboratory Model spray dryer 
operated with an inlet temperature of 215.degree. . The resulting powder 
was a medium grey, free-flowing powder made up of spherical agglomerates, 
characteristic of the spray-drying process. The yield was 13.03 g. 
A portion (1.25 g) of this precursor powder was spread into a thin layer in 
an alumina tray and then heated in air in a furnace from ambient 
temperature to a final heating temperature of 875.degree. at a rate of 
about 20.degree. per minute. The temperature was maintained at 875.degree. 
for 2 hours. The furnace was turned off and allowed to cool below 
100.degree. before the sample was removed. The resulting product was black 
and the yield was 0.72 g. An X-ray diffraction powder pattern of the 
material showed that the product was orthorhombic YBa.sub.2 Cu.sub.3 
O.sub.x, and the results were very similar to those given in Table I. 
There were trace amounts of BaCuO.sub.2 and Y.sub.2 Cu.sub.2 O.sub.5. 
EXAMPLE 7 
Cu(CHO.sub.2).sub.2 (11.06 g, 0.072 mole) was dissolved in 100 cc of 
distilled water with the aid of a few drops of formic acid. The resulting 
solution was heated to 75.degree.. (Ba(OH).sub.2.8H.sub.2 O (15.14 g, 
0.048 mole) and 2.70 g of Y.sub.2 O.sub.3 (0.012 mole) were ground 
together, by hand, using an agate mortar and pestle. The resulting solid 
mixture was then slowly added to the copper formate solution. The 
resulting suspension was kept stirred and heated at about 75.degree. until 
a paste was obtained. This paste was further heated until dry and the 
resulting solid was placed in a vacuum oven at 170.degree. for one hour. 
The solid was then converted to a black powder by hand-grinding using an 
agate mortar and pestle. The X-ray diffraction powder pattern of this 
precursor solid showed that it was a poorly crystalline unidentified phase 
or phases. 
A portion (1.04 g) of this presursor powder was spread into a thin layer in 
an alumina tray and heated in air in a furnace from ambient temperature to 
a final heating temperature of 900.degree. at a rate of about 20.degree. 
per minute. The temperature was maintained at 900.degree. for 2 hours. The 
furnace was turned off and allowed to cool below 100.degree. before the 
sample was removed. The resulting product was black and the yield is 0.67 
g. An X-ray diffraction powder pattern of the material showed that the 
product was orthorhombic YBa.sub.2 Cu.sub.3 O.sub.x, and the results were 
very similar to those given in Table I. There were minor impurity phases 
of BaCuO.sub.2 and Y.sub.2 Cu.sub.2 O.sub.5. 
EXAMPLE 8 
Cu(NO.sub.3).sub.2.6H.sub.2 O (10.65 g, 0.036 mole) was dissolved in 25 cc 
of distilled water. Y(NO.sub.3).sub.3.6H.sub.2 O (5.39 g, 0.012 mole) was 
dissolved in 25 cc of H.sub.2 O. These two solutions were added together 
to yield a mixed solution of copper and yttrium nitrates which was then 
heated to about 75.degree.. Ba(OH).sub.2.8H.sub.2 O (7.57 g, 0.024 mole) 
was then slowly added with stirring to the heated solution. A light blue 
suspension was obtained. This suspension was kept stirred and heated at 
about 75.degree. until a paste was obtained. This paste was further heated 
until dry and the resulting solid was placed in a vacuum oven at 
170.degree. for several hours. The solid was then converted to a light 
blue powder by grinding by hand using an agate mortar and pestle. An X-ray 
diffraction powder pattern of this precursor showed that it to consisted 
of a crystalline unidentified phase or phases. The yield was 14.69 g. 
A portion (1.12) g of this precursor powder was spread into a thin layer in 
an alumina tray and heated in air in a furnace from ambient temperature to 
a final heating temperature of 875.degree. at a rate of about 20.degree. 
per minute. The temperature was maintained at 875.degree. for 2 hours. The 
furnace was turned off and allowed to cool substantially as described in 
previous examples. The resulting powder was black and the yield was 0.62 
g. An X-ray diffraction powder pattern of the material showed that the 
product was orthorhombic YBa.sub.2 Cu.sub.3 O.sub.x, and the results were 
very similar to those given in Table I. There were minor amounts of 
BaCuO.sub.2 and CuO also present. Measurement of the Meissner effect 
showed the powder to have a T.sub.c onset of about 90 K. 
EXAMPLE 9 
Cu(C.sub.2 H.sub.3 O.sub.2).sub.2.H.sub.2 O (7.19 g, 0.036 mole) was 
dissolved in 50 cc of distilled water. The resulting solution was then 
heated to about 75.degree.. BaO.sub.2 (4.06 g, 0.024 mole) and 1.35 g of 
Y.sub.2 O.sub.3 (0.006 mole) were ground by hand using an agate mortar and 
pestle. The resulting solid mixture was slowly added to the heated copper 
acetate solution. Addition had to be extremely slow since it is 
accompanied by the evolution of gas and foaming of the suspension. The 
resulting suspension eventually changed to a blackish-brown color. The 
suspension was kept stirred and heated at about 75.degree. until a paste 
was obtained. This paste was further heated until dry to obtain a solid 
which was placed in a muffle furnace in air at 150.degree. for about 16 
hours. The solid was then converted to a dark brown powder by grinding it 
by hand using an agate mortar and pestle. The yield was 11.24 g. 
A portion (1.11 g) of this precursor powder was spread into a thin layer in 
an alumina tray and heated in air in a furnace from ambient temperature to 
a final heating temperature of 875.degree. at a rate of about 20.degree. 
per minute. The temperature was maintained at 875.degree. for 2 hours. The 
furnace was then turned off and allowed to cool substantially as described 
in the previous examples to give 0.76 g of a black product. An X-ray 
diffraction powder pattern of the product showed that it was orthorhombic 
YBa.sub.2 Cu.sub.3 O.sub.x, and the results were very similar to those 
given in Table I. There were trace amounts of BaCuO.sub.2, Y.sub.2 
Cu.sub.2 O.sub.5 and BaCO.sub.3. 
EXAMPLE 10 
Cu(C.sub.2 H.sub.3 O.sub.2).sub.2.H.sub.2 O (7 294 g, 0.036 mole) was 
dissolved in 100 cc distilled water. The resulting solution was then 
heated to about 75.degree. C. Bi.sub.2 O.sub.3 (8.387 g, 0.018 mole), 
Sr(OH).sub.2.8H.sub.2 O (9.007 g, 0.036 mole) and Ca(OH).sub.2 (1.363 g, 
0.018 mole) were ground by hand using an agate mortar and pestle. The 
resulting solid mixture was slowly added to the heated copper acetate 
solution. The resulting suspension was initially bright blue but within 
five minutes changed to a blackish-brown color. The suspension was kept 
stirred and heated at about 75.degree. C. until a dry solid was obtained. 
The solid was then converted to a dark brown powder by grinding it by 
using an agate mortar and pestle. The yield was 19.87 g. An X-ray 
diffraction powder pattern of this precursor solid showed that it was a 
crystalline unidentified phase or phases. 
A portion (1.11 g) of this precursor powder was heated in air in a furnace 
from ambient temperature to a final heating temperature of 875.degree. C. 
at a rate of about 20.degree. C. per minute. The temperature was 
maintained at 875.degree. C. for 2 hours. The furnace was then turned off 
and allowed to cool to a temperature below 100.degree. C. before the 
sample was removed. The product was black and the yield was 0.79 g. An 
X-ray diffraction powder pattern of the product showed that it was the 
orthorhombic phase with the nominal formula Bi.sub.2 Sr.sub.2 CaCu.sub.2 
O.sub.8+ y plus a small amount of orthorhombic Bi.sub.2 Sr.sub.2 
CuO.sub.6+x. Measurement of the Meissner effect showed the powder to have 
a T.sub.c onset of about 72 K. 
The sample was reground and then heated using essentially the same 
conditions used in the original heating described above. An X-ray 
diffraction powder pattern of the product showed even more orthorhombic 
phase with the nominal formula Bi.sub.2 Sr.sub.2 CaCu.sub.2 O.sub.8+ y 
plus a reduced amount of orthorhombic Bi.sub.2 Sr.sub.2 CuO.sub.6+x. 
Measurement of the Meissner effect showed the powder to have a T.sub.c 
onset of about 82 K. 
EXAMPLE 11 
Cu(C.sub.2 H.sub.3 O.sub.2).sub.2.H.sub.2 O (7.294 g, 0.036 mole) and 
Tl(C.sub.2 H.sub.3 O.sub.2).sub.3 (6.867 g, 0.018 mole) are dissolved in 
150 cc distilled water. The resulting solution was then heated to about 
75.degree. C. Ba(OH).sub.2.8H.sub.2 O (11.357 g, 0.036 mole) and 
Ca(OH).sub.2 (1.363 g, 0.018 mole) are ground by hand using an agate 
mortar and pestle. The resulting solid mixture is slowly added to the 
heated copper and thallium acetate solution. The suspension is kept 
stirred and heated at about 75.degree. C. until a dry solid was obtained. 
The solid is then converted to a powder by grinding it by using an agate 
mortar and pestle. This precursor powder can then be heated in air in a 
furnace to a final heating temperature of about 850.degree. C. to about 
915.degree. C. and maintained at that temperature for 15 minutes to 2 
hours. The product will be the tetragonal phase with the nominal formula 
Tl.sub.2 Ba.sub.2 CaCu.sub.2 O.sub.8+ y.