A Bi-Pb-Sr-Ca-Cu-O system superconductor having a composition of EQU Bi.sub.n Pb.sub.m Sr.sub.x Ca.sub.y Cu.sub.2 O.sub..delta. wherein n is a number from 0.76 to 1.05, m is a number from 0.01 to 0.20, x is a number from 0.85 to 1.35 and y is a number larger than 1.00 and not larger than 1.35; or n is a number larger than 1.06 and not larger than 1.15, m is a number from 0.12 to 0.25, x is a number from 1.20 to 1.35 and y is a number from 1.20 to 1.30; or n is a number larger than 0.75 and not larger than 1.15, m is a number from 0.25 to 0.35, x is a number from 1.20 to 1.35 and y is a number from 1.20 to 1.35, when they are normalized with the Cu mole number of 2, which has t.sub.c of at least 110 K.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to Bi-Pb-Sr-Ca-Cu-O system superconductors 
which have a zero resistance critical temperature (T.sub.c) of at least 
107 K. or 108 K., in some cases, at least 110 K. 
2. Description of the Related Art 
In 1988, the researchers in the National Institute for Metals, Japan found 
a Bi-Sr-Ca-Cu-O system superconductor having T.sub.c of 105 K. which was 
obtained by extrapolation of the measured date. However, hitherto, it has 
been believed that it is very difficult to produce a Bi-Sr-Ca-Cu=O system 
superconductor which has T.sub.c of 105 K. or higher and contains a high 
T.sub.c phase in a large volume percentage with good reproducibility. 
The present inventors synthesized a superconductor comprising a 
Bi-Sr-Ca-Cu-O system to which Pb is added and found that such new 
Bi-Pb-Sr-Ca-Cu-O system superconductor had T.sub.c of 107 K. However, it 
is still difficult to produce the Bi-Pb-Sr-Ca-Cu-O system superconductor 
having T.sub.c of 107 or higher and containing the high T.sub.c phase in a 
larger volume percentage with good reproducibility. Very few scientists 
have been able to synthesize such superconductor. 
The Y-Ba-Cu-O system superconductor which was found in 1987, the 
Bi-Sr-Ca-Cu-O system superconductor and the Bi-Pb-Sr-Ca-Cu-O system 
superconductor have T.sub.c higher than the liquid nitrogen temperature, 
namely 77 K. and attract great attention worldwidely. But, it is still 
desired to provide a superconductor having higher T.sub.c since when 
difference between the liquid nitrogen temperature and T.sub.c is greater, 
the superconductor has better and more stable superconductive 
characteristics. 
SUMMARY OF THE INVENTION 
One object of the present invention is to provide a Bi-Pb-Sr-Ca-Cu-O system 
superconductor having T.sub.c of at least 110 K. 
Another object of the present invention is to provide a Bi-Pb-Sr-Ca-Cu-O 
system superconductor which can be synthesized with good reproducibility. 
These and other objects are achieved by a Bi-Pb-Sr-Ca-Cu-O system 
superconductor having T.sub.c of at least 110 K. and a composition of 
EQU Bi.sub.n Pb.sub.m Sr.sub.x Ca.sub.y Cu.sub.2 O.sub..delta. 
wherein n is a number from 0.76 to 1.05, m is a number from 0.01 to 0.20, x 
is a number from 0.85 to 1.35 and y is a number larger than 1.00 and not 
larger than 1.35, or 
n is a number larger than 1.06 and not larger than 1.15, m is a number from 
0.12 to 0.25, x is a number from 1.20 to 1.35 and y is a number from 1.20 
to 1.30, or 
n is a number larger than 0.75 and not larger than 1.15, m is a number from 
0.25 to 0.35, x is a number from 1.20 to 1.35 and y is a number from 1.20 
to 1.35, when they are normalized with the Cu mole number of 2.

DETAILED DESCRIPTION OF THE INVENTION 
In the first embodiment, the Bi-Pb-Sr-Ca-Cu-O system superconductor of the 
present invention has a composition of 
EQU Bi.sub.n Pb.sub.m Sr.sub.x Ca.sub.y Cu.sub.2 O.sub..delta. 
wherein n is a number from 0.76 to 1.05, m is a number from 0.01 to 0.20, x 
is a number from 0.85 to 1.35 and y is a number larger than 1.00 and not 
larger than 1.35. With this composition, the Bi-Pb-Sr-Ca-Cu-O system 
superconductor has T.sub.c of 110 K. or higher and contains the high 
T.sub.c phase in a larger volume percentage and can be synthesized with 
good reproducibility. When n is a number from 0.80 to 0.95, m is a number 
from 0.04 to 0.20, x is a number from 0.90 to 1.30 and y is a number 
larger than 1.00 and not larger than 1.30, the superconductor has T.sub.c 
of 110K or higher easily and contains the high T.sub.c phase in a large 
volume percentage. 
In the second embodiment, the superconductor of the present invention has a 
composition of 
EQU Bi.sub.n Pb.sub.m Sr.sub.x Ca.sub.y Cu.sub.2 O.sub..delta. 
wherein n is a number larger than 1.06 and not larger than 1.15, m is a 
number from 0.12 to 0.25, x is a number from 1.20 to 1.35 and y is a 
number from 1.20 to 1.30. With this composition, the Bi-Pb-Sr-Ca-Cu-O 
system superconductor has T.sub.c of 110K or higher and contains the high 
T.sub.c phase in a larger volume percentage and can be synthesized with 
good reproducibility. Preferably, n is a number larger than 1.05 and not 
larger than 1.12, m is a number from 0.15 to 0.23, x is a number from 1.25 
to 1.35 and y is a number from 1.25 to 1.30. 
In the third embodiment, the superconductor of the present invention has a 
composition of 
EQU Bi.sub.n Pb.sub.m Sr.sub.x Ca.sub.y Cu.sub.2 O.sub..delta. 
wherein n is a number larger than 0.76 and not larger than 1.15, m is a 
number from 0.25 to 0.35, x is a number from 1.20 to 1.35 and y is a 
number from 1.20 to 1.35. 
The superconductive compound of the present invention can be produced as 
follows: 
First, as raw materials, Bi.sub.2 O.sub.3, SrCO.sub.3, CaCO.sub.3, CuO and 
PbO are weighed in a desired molar ratio and mixed, or carboxylates such 
as oxalates containing Bi, Pb, Sr, Ca and Cu in a desired molar ratio are 
synthesized by a coprecipitation method. In this step, the molar ratio of 
Bi, Sr, Ca and Cu may be almost the same as that in the final product, 
while Pb may be used in a ratio more than that in the final product since 
a part of Pb is evaporated during thermal treatment. 
When the mole number of Cu is 2, the preferred molar ratios of other 
elements in the raw material are, in the first embodiment, 
EQU 0.76&lt;n&lt;1.15, 
EQU 0.25&lt;m&lt;0.60, 
EQU 1.00&lt;x&lt;1.40 and 
EQU 1.00&lt;y&lt;1.40, 
in the second embodiment, 
EQU 1.06&lt;n&lt;1.20, 
EQU 0.15&lt;m&lt;0.60, 
EQU 1.15&lt;x&lt;1.40 and 
EQU 1.15&lt;y&lt;1.35, 
or in the third embodiment, 
EQU 0.76&lt;n&lt;1.20, 
EQU 0.25&lt;m&lt;0.80, 
EQU 1.15&lt;x&lt;1.40 and 
EQU 1.15&lt;y&lt;1.40. 
Then, the oxide mixture or the carboxylate mixture is heated and reacted in 
the air at about 800.degree. C. When the carboxylates are used, preferably 
the mixture is thermally decomposed at about 250.degree. C. and then 
reacted at about 800.degree. C. The heated mixture is ground and 
pelletized under pressure of about 500 to 1000 kg/cm.sup.2. Finally, the 
pellet is sintered at a temperature of 845.degree. to 865.degree. C. 
PREFERRED EMBODIMENTS OF THE INVENTION 
The present invention will be illustrated by following Examples. 
Example 1 
To a solution of nitrates of Bi, Pb, Sr, Ca and Cu, ammonium oxalate was 
added to coprecipitate oxalates in which the molar ratio of Bi:Pb:Sr:Ca:Cu 
was 0.90:0.51:1.18:1.18:2.00. The coprecipitated oxalates were dried at 
100.degree. C., heated at 250.degree. C. to decompose them and ground 
followed by heating with an electric furnace in the air at 800.degree. C. 
for 12 hours. Thereafter, the mixture was again ground and pressed under 
pressure of about 1000 kg/cm.sup.2 to produce a pellet of 20 mm in 
diameter and 2 mm in thickness. The pellet was sintered with the electric 
furnace in the air at 855.degree. C. for 120 hours. 
With the sintered sample, the molar ratio of the component elements was 
examined with ICAP to find that the molar ratio of Bi:Pb:Sr:Ca:Cu was 
0.85:0.10:1.15:1.13:2.00 when normalized with the mole number of Cu of 2. 
The temperature dependence of the electrical resistance of this sample is 
shown in FIG. 1, from which it is understood that the electrical 
resistance quickly dropped from about 130K and reached 0 (zero) at about 
115K. The A.C. magnetic susceptibility of this sample is shown in FIG. 2, 
which confirms that this sample could be superconductive at about 115K or 
higher. The X-ray diffraction pattern of this sample is shown in FIG. 3, 
which indicates that the percentage of the high T.sub.c phase with the c 
axis of 37 .ANG. in this sample was substantially 100%. 
Example 2 
To a solution of nitrates of Bi, Pb, Sr, Ca and Cu, ammonium oxalate was 
added to coprecipitate oxalates in which the molar ratio of Bi:Pb:Sr:Ca:Cu 
was 0.88:0.45:1.20:1.20:2.00. The coprecipitated oxalates were dried at 
100.degree. C., heated at 500.degree. C. to decompose them and ground 
followed by heating with an electric furnace in the air at 800.degree. C. 
for 12 hours. Thereafter, the mixture was again ground and pressed under 
pressure of about 600 kg/cm.sup.2 to produce a pellet of 20 mm in diameter 
and 2 mm in thickness. The pellet was sintered with the electric furnace 
in the air at 844.degree. C. for 192 hours. 
With the sintered sample, the molar ratio of the component elements was 
examined with ICAP to find that the molar ratio of Bi:Pb:Sr:Ca:Cu was 
0.81:0.07:1.16:1.15:2.00 when normalized with the mole number of Cu of 2. 
The temperature dependence of the electrical resistance of this sample is 
shown in FIG. 4, from which it is understood that the electrical 
resistance quickly dropped from about 130K and reached 0 (zero) at about 
114K. The A.C. magnetic susceptibility of this sample is shown in FIG. 5, 
which confirms that this sample could be superconductive at about 114K or 
higher. The X-ray diffraction pattern of this sample is shown in FIG. 6, 
which indicates that the percentage of the high T.sub.c phase with the c 
axis of 37 .ANG. was about 90%. 
Example 3 
In the same manner as in Example 2 but sintering the pressed pellet at 
855.degree. C. for 120 hours, the sample was prepared in which the molar 
ratio of Bi:Pb:Sr:Ca:Cu was 0.82:0.09:1.17:1.15:2.00. 
The zero resistance critical temperature of this sample was 112K, and the 
A.C. magnetic susceptibility of this sample confirmed that this sample was 
superconductive at about 114K or higher. The X-ray diffraction pattern of 
this sample indicated that the percentage of the high T.sub.c phase was 
about 80%. 
Example 4 
In the same manner as in Example 2 but coprecipitating the oxalates in the 
molar ratio of Bi:Pb:Sr:Ca:Cu of 1.02:0.57:1.30:1.30:2.00, the sample was 
prepared. According to the ICAP analysis, the molar ratio of 
Bi:Pb:Sr:Ca:Cu in the sample was 0.95:0.09:1.25:1.24:2.00. 
The electric resistance of this sample sharply dropped from about 130K and 
reached 0 (zero) at 112K. The X-ray diffraction pattern of this sample 
indicated that the percentage of the high T.sub.c phase was larger than 
about 80%. 
Example 5 
In the same manner as in Example 3 but coprecipitating the oxalates in the 
molar ratio of Bi:Pb:Sr:Ca:Cu of 0.92:0.50:1.20:1.20:2.00, the sample was 
prepared. According to the ICAP analysis, the molar ratio of 
Bi:Pb:Sr:Ca:Cu in the sample was 0.87:0.07:1.17:1.15:2.00. 
The electric resistance of this sample sharply dropped from about 130K and 
reached 0 (zero) at 112K. The X-ray diffraction pattern of this sample 
indicated that the percentage of the high T.sub.c phase was larger than 
about 80%. 
Examples 6 and 7 
Bi.sub.2 O.sub.3, PbO, SrCO.sub.3, CaCO.sub.3 and CuO were weighed in a 
molar ratio of Bi:Pb:Sr:Ca:Cu of 
1.08:0.50:1.30:1.30:2.00 (Example 6) or 
0.85:0.40:1.15:1.15:2.00 (Example 7) 
and ground and mixed in an agate mortar. Then, the ground mixture was 
placed in an alumina boat and heated and reacted with an electric furnace 
in the air at 800.degree. C. for 24 hours. The mixture was again ground in 
the mortar and pressed under pressure of about 600 kg/cm.sup.2 to produce 
a pellet of about 20 mm in diameter and 2 mm in thickness. The pellet was 
sintered with the electric furnace in the air at 855.degree. C. for 120 
hours. 
With the sintered sample, the molar ratio of the component elements was 
examined with ICAP to find that the molar ratio of Bi:Pb:Sr:Ca:Cu was 
1.01:0.18:1.27:1.25:2.00 (Example 6), or 
0.80:0.14:1.10:1.09:2.00 (Example 7) 
when normalized with the mole number of Cu of 2. 
The electrical resistance of each sample quickly dropped from about 130K 
and reached 0 (zero) at about 112K, about 111K and about 110K in Examples 
6, 7 and 8, respectively. The A.C. magnetic susceptibility of each sample 
confirmed that this sample could be superconductive at the respective 
critical temperature or higher. The X-ray diffraction pattern of each 
sample indicated that the percentage of the high T.sub.c phase was about 
80%. 
Example 8 
To a solution of nitrates of Bi, Pb, Sr, Ca and Cu, ammonium oxalate was 
added to coprecipitate oxalates in which the molar ratio of Bi:Pb:Sr:Ca:Cu 
was 1.15:0.30:1.30:1.30:2.00. The coprecipitated oxalates were dried at 
100.degree. C., heated at 500.degree. C. to decompose them and ground 
followed by heating with an electric furnace in the air at 800.degree. C. 
for 12 hours. Thereafter, the mixture was again ground and pressed under 
pressure of about 600 kg/cm.sup.2 to produce a pellet of 20 mm in diameter 
and 2 mm in thickness. The pellet was sintered with the electric furnace 
in the air at 850.degree. C. for 24 hours. The grinding and pressing were 
repeated and the pellet was again sintered with the electric furnace in 
the air at 850.degree. C. for 48 hours. 
With the sintered sample, the molar ratio of the component elements was 
examined with ICAP to find that the molar ratio of Bi:Pb:Sr:Ca:Cu was 
1.098:0.153:1.266:1.243:2.00 when normalized with the mole number of Cu of 
2. 
The temperature dependence of the electrical resistance of this sample is 
shown in FIG. 7, from which it is understood that the electrical 
resistance quickly dropped from about 130K and reached 0 (zero) at about 
111K. The X-ray diffraction pattern of this sample is shown in FIG. 8, 
which indicates that the percentage of the high T.sub.c phase with the c 
axis of 37 .ANG. was about 98%. 
Example 9 
To a solution of nitrates of Bi, Pb, Sr, Ca and Cu, ammonium oxalate was 
added to coprecipitate oxalates in which the molar ratio of Bi:Pb:Sr:Ca:Cu 
was 1.10:0.35:1.32:1.32:2.00. The coprecipitated oxalates were dried at 
100.degree. C., heated at 500.degree. C. to decompose them and ground 
followed by heating with an electric furnace in the air at 800.degree. C. 
for 12 hours. Thereafter, the heated mixture was again ground and pressed 
under pressure of about 1000 kg/cm.sup.2 to produce a pellet of 20 mm in 
diameter and 2 mm in thickness. The pellet was sintered with the electric 
furnace in the air at 850.degree. C. for 120 hours. 
With the sintered sample, the molar ratio of the component elements was 
examined with ICAP to find that the molar ratio of Bi:Pb:Sr:Ca:Cu was 
1.075:0.165:1.298:1.285:2.00 when normalized with the mole number of Cu of 
2. 
The temperature dependence of the electrical resistance of this sample is 
shown in FIG. 9, from which it is understood that the electrical 
resistance quickly dropped from about 130 K. and reached 0 (zero) at about 
112 K. The A.C. magnetic susceptibility of this sample is shown in FIG. 
10, which confirms that this sample could be superconductive at about 112 
K. or higher. The X-ray diffraction pattern of this sample is shown in 
FIG. 11, which indicates that the percentage of the high T.sub.c phase 
with the c axis of 37 .ANG. was about 90%. 
Example 10 
To a solution of nitrates of Bi, Pb, Sr, Ca and Cu, ammonium oxalate was 
added to coprecipitate oxalates in which the molar ratio of Bi:Pb:Sr:Ca:Cu 
was 0.77:0.55:1.24:1.33:2.00. The coprecipitated oxalates were dried at 
100.degree. C., heated at 500.degree. C. to decompose them and ground 
followed by heating with an electric furnace in the air at 800.degree. C. 
for 12 hours. Thereafter, the mixture was again ground and pressed under 
pressure of about 600 kg/cm.sup.2 to produce a pellet of 20 mm in 
diameter and 2 mm in thickness. The pellet was sintered with the electric 
furnace in the air at 850.degree. C. for 24 hours. Then, grinding, 
pressing and formation of a pellet were repeated and again the pellet was 
sintered with the electric furnace in the air at 850.degree. C. for 80 
hours. 
With the sintered sample, the molar ratio of the component elements was 
examined with ICAP to find that the molar ratio of Bi:Pb:Sr:Ca:Cu was 
0.725:0.332:1.218:1.295:2.00 when normalized with the mole number of Cu of 
2. 
The temperature dependence of the electrical resistance of this sample is 
shown in FIG. 12, from which it is understood that the electrical 
resistance quickly dropped from about 130 K. and reached 0 (zero) at about 
112 K. The A.C. magnetic susceptibility of this sample is shown in FIG. 
14, which confirms that this sample could be superconductive at about 112 
K. or higher. The X-ray diffraction pattern of this sample is shown in 
FIG. 13, which indicates that the percentage of the high T.sub.c phase 
with the c axis of 37 .ANG. in this sample was about 70%. 
Example 11 
In the same manner as in Example 10 but coprecipitating oxalates in which 
the molar ratio of Bi:Pb:Sr:Ca:Cu was 1.19:0.41:1.24:1.34:2.00 and 
carrying out the last sintering at 850.degree. C. for 72 hours, a 
superconductive oxide in which a molar ratio of Bi:Pb:Sr:Ca:Cu was 
1.140:0.261:1.223:1.288:2.00 was produced. This sample had a zero 
resistance critical temperature of about 110 K., the X-ray diffraction 
pattern of this sample indicated that the percentage of the high T.sub.c 
phase was about 70%.