JPH03170335A - Oxide super conductor and its preparation - Google Patents

Abstract

PURPOSE:To improve the critical temperature of an oxide superconductor while depressing the production of Ca2PbO4 by calcining the molded product of a specific metal oxide in an oxide-containing atmosphere. CONSTITUTION:The powder of a mixture comprising the carbonates, etc., of respective elements is calcinated at 700-845 deg.C and subsequently molded into a molded product comprising the oxides of Bi, Pb, Sr, Ca, Cu and, Na and/or Li in a molar ratio of 2:(1.5-2.2):(0.1-0.5):(2.0-3.5):(3.0-4.5):(0.01-0.5). The molded product is calcined at 820-850 deg.C for 100 hours or more to provide an oxide superconductor having a critical temperature of 100K or higher.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field 1 The present invention is directed to Bi-Sr-
The present invention relates to a CaCu-0-based oxide superconductor and a method for producing the same.

[Prior art] Currently, as superconductors, NbTi, Nb+Sn
Metal-based superconductors represented by
However, in recent years, Physical Re
view. Letters 5B (197B) pp90
In B-910, a complex oxide made of transition metals, alkaline earth elements, and copper that exhibits superconductivity at temperatures above 77 K has been reported, and it has become possible to use it at inexpensive liquid nitrogen temperatures in place of expensive liquid helium. , its uses are expanding significantly.

For such an oxide superconductor, its critical temperature T
Research has been conducted to further increase c, and recently, Ja
p. J. App+. Letters 27 (1988)
At L209, the critical temperature Tc is IIOK or 8
A 0K Bi-Sr-Ca-Cu-0 superconducting oxide has been reported and has attracted attention.

[Problem to be Solved by the Invention 1] However, when producing the above-mentioned Bi-Sr-Ca-Cu-0 based superconductor as a sintered body (bulk body), the critical temperature Tc in the sintered body is different from the IIOK phase. 80K phase is mixed, 8
There was a problem in that the Tc of the sintered body itself could not be increased because the 0K phase behaved like an impurity.

Incidentally, the 110K phase of these currently known phases is B.
izSr2CazCu30+ o. (80K phase is Bi.
Sr2Ca+CuzO8. It is said to be t.

As a technology for converting this 110K phase into a single phase, see Jap. J
．． Appl. Phys Vo127, No. 6 (198
B) In L 1041-1043, Takano et al. reported that the content of the 110K phase was increased by adding Pb. However, the addition of Pb has the disadvantage that stable CazPb04 grows in the grain boundaries and the superconducting properties deteriorate.

[1,000 Steps to Solve the Problems The present inventors have conducted repeated research on the above points, and have found that the Bi-Pb-Sr-Ca-Cu-0 system is effective due to specific ratios. By adding Na and Li compounds in a specific ratio, the sintering temperature can be lowered, and
It has been found that it is possible to promote the growth of the 110K phase while suppressing the growth of Ca2Pb04, and to provide an oxide superconductor having a high critical temperature and a high content of the IIOK phase.

That is, the oxide superconductor of the present invention can be manufactured using Bi, Pb, Sr, Ca, Cu, and Na as its constituents.
, Li, and the molar ratio of each of these metal elements is 1.8 to 2.2 for Bi and 0.2 for Pb, when the number of moles of Sr is 2.
1 to 0.6, Ca 2.0 to 3.5, Cu 3
．． 0 to 4,5, the total amount of Na and Li is 0. Ol~0.
This method is characterized by firing a certain shape having a ratio of 5% to 820°C to 850°C in an oxygen-containing atmosphere, and the composition of the obtained superconductor is determined by the number of moles of Sr in the molar ratio of the constituent metals. When Bi is set to 2, Bi is 1.8 to 2.
．． 2, Pb is 0.1 to 0.5, Ca is 2.0 to 3.5, Cu is 3.0 to 4.5, and the total amount of Na and Li is 0.01 or less to achieve criticality. temperature(
Tc) 100K or more can be achieved.

−　3　− The present invention will be explained in detail below.

One of the features of the present invention is that due to the manufacturing method, when the molar ratio of each metal element present as a composite oxide is set within a specific range, that is, when the number of moles of Sr is 2, Bi is 1.8 to 2. 2.2, Ca 2.0 to 3.5, Cu 3.0
The ratio is adjusted to 4.5 to 4.5, and for this system, Pb is adjusted to 0.1 to 0.6 and Na and Li are adjusted to a ratio of 0.01 to 0.5 in total to Sr. It is in. As described in the prior art, the effect of adding Pb can promote the growth of the IIOK phase, but the addition of Pb can promote the growth of the IIOK phase.
bO. The impurities in the product are absorbed and the properties deteriorate. Therefore, by adding Na or Li, the firing temperature is lowered and the following formula 2B+zSrzCa+CuzOy →Bi2Sr2Ca
zCu30y'10BizSrzCuOy'' promotes the conversion of the 80K phase superconductor produced in the firing process into the 110K phase superconductor, suppresses the generation of Ca2Pb04, and improves the grain size of the sintered body. The influence of interfacial precipitates can be reduced.

The reason for limiting the starting group weight to the above range is as follows.
Among the metal elements, if any of Bi, Ca, and Cu is less than the above-mentioned range, a large amount of 80K phase remains, and if it is too much, an impurity phase grows and a superconducting phase may not be formed. If Pb is less than 0.1, the sintering rate will be slow and the 110K phase will be less viable, and if it exceeds 0.6, Ca! Impurities such as PbO4 grow and the critical temperature (
Tce) and critical current density (Jc).

Furthermore, if the total amount of NaaLi is less than 0.01, the firing temperature of the system will increase, resulting in an increase in Ca2PbO4, and it will not be possible to increase the amount of 110K phase produced.
．． This is because if it exceeds 5, the normal phase increases at the grain boundaries, lowering Tc.

Among the starting composition ranges mentioned above, in particular, the molar ratio of Bi to S r = 2 is 1.9 to 2.0, and Pb is 0.
．． It is better to prepare the mixture so that the total amount of Ca is 3.1 to 3.2, Cu is 4.1 to 4.3, and the total amount of Na and Li is 0.05 to 0.20. Ta1
A superconductor with a high content of 10K phase can be obtained.

According to the present invention, the above-mentioned precepts are made of oxides of each metal or those that can be converted into oxides by incineration,
For Na, Li, fluoride, chloride, oxalide,
Iodide also applies. For example, a blended powder prepared in the form of carbonate, or a blended powder at a temperature of 700 to 845°C, for example.
The calcined powder is then calcined at a temperature of A method such as placing it in a silver pipe and rolling it is adopted.

Further, if the 110K phase is formed by calcining at 830° C. or higher, the crystal grains become larger and can be oriented during shaping.

Next, the above-mentioned shaped product is heated to 820 to 850°C, especially 835 to 835°C.
A superconductor having a high 110 K phase content can be obtained by firing at a temperature of 845 DEG C. in an oxidizing atmosphere such as air that can supply sufficient oxygen to the system.

Under the above firing conditions, if the firing temperature is lower than 820°C, the superconducting compound will not coalesce, and if it is higher than 850°C, CazP
Impurities such as b04 are present.

Further, the firing time is preferably 100 hours or more,
If it is shorter than 100 hours, the low Tc phase such as the 80K phase occupies most of the time, and there is a tendency that the IIOK phase cannot be made into a single phase.

According to this firing, Pb in the starting group is dissolved in the superconducting phase and substituted at Bi sites, but Na or Li is not dissolved in the superconducting phase and exists at the grain boundaries. Most tend to evaporate. This Na compound or Li
If the compound is present in the final sintered body, it will have an adverse effect on the superconducting properties, so it is necessary to actively volatilize it during sintering.

Therefore, according to the present invention, when the molar ratio of Sr is set to 2, Bi is 1.8 to 2.2, particularly 1.9 to 2.1, Pb is 0.1 to 0.5, especially 0.4 to 0.5, and Ca is 2.0 to 3.
．． 5, especially 3.0 to 3.1, and Cu of 3.0 to 4.
5, especially 4.0 to 4.2, and the total amount of Na and Li is 0.
01 or less, especially 0.001 to o. An excellent superconductor with a critical temperature Tce of 100K or higher can be obtained by adjusting the volatilization amount of Pb, Na, or Li by the firing time or the like so that the amount falls within the range of oos.

7. The amount of oxygen in the superconductor of the present invention is not certain, but there is no restriction on it except that during firing, the atmosphere is maintained in an atmosphere that can sufficiently supply the oxygen required by the system itself.

The characteristics of the oxide superconductor of the present invention obtained in this way include an 80K phase, a Ca. The production of impurity phases such as Pb04 is small, and the critical temperature is higher than 100K (Tce
), as is clear from the comparison between Figures 2 and 3, conventionally, in a magnetic field of 8 (Oe),
．． In liquid helium at 2K, the superconducting phase decreases from about 90% to about 50% in a zero magnetic field, whereas the product of the present invention shows almost no change even in a magnetic field of 8 (Oe), which is an entirely unexpected and excellent property. It has characteristics. The reason for this phenomenon is not clear, but by suppressing the vitality of grain boundary precipitates, weakly bonded portions of grain boundaries (
This is thought to be due to the fact that the weak link) is eliminated, making the material less susceptible to magnetic fields.

The invention will now be explained with the following examples.

9-8 [Example] BizOs, PbO, SrCOs, Ca as raw material powder
C.O. ,, CuO powders were weighed so that the molar ratio of each metal was as shown in Table 1, calcined at 750 to 810°C for 20 hours, and then ground to obtain calcined powders with an average particle size of 5μ. . For this calcined powder, Na 2 C0 3 + L I 2
CO
A disk-shaped sample with a thickness of about 1 mm was prepared.

This sample was incinerated under the conditions shown in Table 1.

The specific gravity of the obtained sintered body was determined by the Archimedes method.
The critical temperature (Tce) was determined from the electrical resistance change, and the superconductor ratio at 90K was determined from the AC magnetic susceptibility measurement.

The results are shown in Table 1.

(The following is a margin) - IO - In the table, No. with added Na. 2 and all<Na or L
No. i was not added. The X-ray diffraction chart of sample No. 1 is shown in FIG. According to FIG. 1, conventional product No.
l is 80K phase and Ca. A peak of PbO was observed, whereas a peak of PbO was observed, whereas a peak of PbO. 2 is the peak of 80K phase and C
It is understood that the phase of a2PbO, is smaller.

Next, for the same sample used in FIG. 1, the relationship between temperature resistance and magnetic susceptibility versus temperature is shown in FIG. 2, respectively.
2. Figure 3 shows conventional product No. l is illustrated.

According to a comparison between Figures 2 and 3, the conventional product in Figure 3 has an onset temperature of around 110K in the temperature-resistance curve.
Although there was a temperature difference of 1 degree (Tco), there was a step near the middle, and the offset temperature (Tce) was 89K. This means that although the 110K phase is included, different phases such as an 80K phase are present.

In addition, in the temperature-magnetic susceptibility curve, 0.8 (Oe) in liquid helium at 4.2 K is as high as about 88%, but 8 (
It can be seen that the magnetic susceptibility changes greatly at approximately 52% for Oe).

On the other hand, in the temperature-resistance curve of the product of the present invention shown in FIG. 2, the resistance value near 200K is as small as about 41IlΩ, and the onset temperature (Tco) is near 120K.
It decreases monotonically without creating a step as shown in Figure 3,
The offset temperature (Tce) shows a high value of 107K,
It can be seen that there are almost no foreign phases such as 80K.

In addition, the temperature-magnetic susceptibility curve shows a high magnetic susceptibility of about 98% at 4.2 K, and there is almost no change in the curve even in a magnetic field of 8 (Oe), indicating that it is strong against magnetic fields.

On the other hand, according to Table 1, the total amount of Na and Li added is S
Sample No. exceeding 0.5 for r-2. 4. 10.
No. 13 had a large amount remaining in the final sintered body and did not exhibit a high critical temperature. In addition, sample N with too little Bi content
Almost no superconductor was produced in o5. Also,
When the amount of PbO was small, the critical temperature was low and the proportion of superconducting phase was also low.

In contrast, all samples of the present invention have a critical temperature of 100K.
In addition, the production ratio of the superconducting phase was more than 80%.

[Effect of the Invention 1 As detailed above, according to the present invention, Bi-PbSr
By adding an appropriate amount of Na or Li to the -Ca-Cu-0 superconductor, precipitation of the 80K phase and other impurities can be suppressed, and by containing a large amount of the 110K phase, a high critical temperature (Tc) can be imparted. In addition, it is possible to obtain an excellent superconductor whose properties change little with respect to changes in the magnetic field, and it is possible to apply it to various electronic components by inserting a magnetic shielding material therein.

[Brief explanation of the drawing]

FIG. 1 shows the present invention product Nα2 and the conventional product No. The X-ray diffraction chart for No. 1, FIG. 2, and FIG. 3 all show the relationship between temperature and resistance and temperature and magnetic susceptibility. 2. Figure 3 is the conventional product No. 1 is shown.

Claims (2)

[Claims] (1) Consists of Bi, Pb, Sr, Ca, Cu, at least one of Na, Li, and oxygen as metal elements, and when the molar ratio of each metal element is set to 2 moles of Sr, Bi is 1.8 to 2.2, Pb 0.1 to 0.5
, Ca is 2.0 to 3.5, Cu is 3.0 to 4.5,
The critical temperature (Tce
) is an oxide superconductor with a temperature of 100K or more. (2) Consists of an oxide of Bi, Pb, Sr, Ca, Cu, and at least one of Na and Li as constituent elements,
When the number of moles of Sr is 2 in the molar ratio of each metal,
Bi: 1.8 to 2.2, Pb: 0.1 to 0.5, C
a is 2.0 to 3.5, Cu is 3.0 to 4.5, Na
, Li in a total amount of 0.01 to 0.
A method for producing an oxide superconductor, which comprises firing a molded body having a ratio of 5 to 5 in an oxygen-containing atmosphere at 820 to 850°C.