JP2893405B2 - Bi-Pb-Sr-Ca-Cu-o based superconducting material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention has recently attracted attention as a possibility of exhibiting superconductivity at a boiling point of liquid nitrogen of 77K or higher, and in some cases even higher temperature of 100K or higher. -Pb for Sr-Ca-Cu-O-based material
The present invention relates to a superconducting substance containing.

[Conventional technology]

Recently, the electrical resistance of a sintered body of Bi ₁ Sr ₁ Ca ₁ Cu ₂ composition began to decrease at 120 K from the Institute for Metals, and then dropped sharply to about 107 K. Was announced. According to the announcement, this material has a superconducting transition end point of about 105K (value obtained by extrapolating from experimental data) and a superconducting phase (high Tc phase) of about 75K at which the electrical resistance becomes zero.
It is said that there are two types of superconducting phases (low Tc phase), and the whole is not completely a high Tc phase sample. However, this substance has a Meissner effect. It was to be done.

It has also been reported that this substance is a superconducting substance containing no rare earth elements, and is also characterized by being stable in water and the like as compared with the Y-Ba-Cu-O system.

After this announcement, not only in Japan and the United States, but also around the world,
An additional test was conducted, one example of which is as follows.

In other words, the inorganic materials laboratory, etc., use Bi ₂ (Ca, Sr) ₃ Cu ₂ O ₉ or Bi ₂
It has been announced that the electrical resistance of the sintered body having the composition of (Ca, Sr) _3-x Cu ₂ O _{9 -y} starts to decrease from about 110K and becomes zero at about 70 to 40K.

[Problems to be solved by the invention]

Bi-Ca-Sr-Cu-O-based materials announced to date have high Tc
Phase and low Tc phase are mostly mixed, and their chemical compositions are also variously different.

According to additional tests by the present inventors, this material also requires a heat treatment temperature just below the melting point of the sample to produce a high critical temperature material, and synthesis conditions are extremely limited. It is known.

The present inventors have attempted to overcome these disadvantages by using Bi-Sr-Ca
While adding Pb to the -Cu-O system, changing the composition ratio of the component elements and changing the heat treatment conditions repeatedly, the superconducting critical temperature is at least the boiling point of liquid nitrogen 77K or more, and 105K depending on the conditions. The inventors have succeeded in synthesizing the above substances, and have reached the present invention.

[Means for solving the problem]

That is, the present invention relates to Bi ₁ Sr ₁ Ca ₁ C
It is intended to provide a substance in which Pb is contained in u ₂ O _x , and in addition to this, a substance in which the composition ratio of each of the constituent elements is changed, and more specifically, Bi-Pb-Sr-Ca- a Cu-O-based oxide, constituent elements Bi, Pb, Sr, Ca, number of moles is Bi _n of Cu, Pb
_m , Sr _x , Ca _y , Cu _z (n, m, x, y, z are 0.5 <2.6,0.01 ≦ m ≦ 1.5,
1.5 ≦ x ≦ 2.2, 0.8 ≦ y ≦ 2.2, 2.0 ≦ z ≦ 4.0)
Bi-Pb-Sr-Ca-Cu-O superconducting material represented by
Bi-Pb-Sr-Ca-Cu-O with superconducting critical temperature above 0K
A superconducting material is provided.

Thus, the present invention provides Pb to the conventional Bi-Sr-Ca-Cu-O system.
In this case, the content of Pb, that is, m
When the value is larger than 1.5, the substance often becomes a semiconductor, and when the value is smaller than 0.01, the substance is not much different from the conventional one in which Pb is not added.

The above compound can be produced by the following method.

That is, Bi ₂ O ₃ , SrCO ₃ , CaCO ₃ , CuO and PbO as starting materials are weighed and mixed at desired ratios as starting materials, respectively, or Bi, P
An oxalate containing each of b, Sr, Ca, and Cu in a desired ratio is synthesized by a precipitation method. At this time, Bi, Sr, Ca, and Cu may have a desired composition ratio, but Pb evaporates during a heat treatment performed later, so that Pb needs to be added so as to have a target composition ratio of Pb or more. The mixed powder or oxalate is subjected to a solid-phase reaction by heating at about 800 ° C. in the air.
When the thermal decomposition is carried out at, it is preferable to carry out a heating reaction at about 800 ° C. Thereafter, this is pulverized and pressurized at about 1000 kg / cm ² to form a pellet, and then fired at 810 ° C. to 880 ° C.

Hereinafter, the relationship between the properties of the generated Bi-Pb-Sr-Ca-Cu-O-based superconducting material, the ratio of the number of moles of the constituent elements, and the manufacturing conditions will be described more specifically.

First, the superconducting critical temperature of the generated superconducting material is greatly affected by the molar ratio of the constituent elements. Cu 2
When the range of the ratio of the number of moles of other constituent elements is shown as
_A preferable range is _{0.7 to 1.2} Pb _{0.04 to 0.2} Sr _{1.0 to 1.3} Ca _{1.0 to 1.3} Cu ₂ , and a superconducting substance in this range has a high probability of achieving a superconducting critical temperature of 100K or more.

Next, the production method, in the production of the superconducting material according to the present invention, in the case where the raw material powder is directly mixed to prepare a predetermined composition ratio, and oxalate having a predetermined composition ratio by a precipitation method,
In the case of preparing by precipitation as a carboxylate such as citrate, the latter preparation method is more reproducible in the production method in that the same target product is obtained, and the high Tc phase It is easy to obtain a target with a high ratio.

〔Example〕

Example 1 Bi ₂ O ₃ , PbO, SrCO ₃ , CaCO ₃ and CuO were weighed as raw material powders such that the molar ratios of the constituent elements were Bi _2.0 , Pb _0.6 , Sr ₂ , Ca ₂ , and Cu _3.6. After sufficiently mixing and pulverizing in a mortar, the mixture was placed in an alumina board and subjected to a heating solid phase reaction in air at 800 ° C. for 24 hours in an electric furnace to obtain a black powder. After the powder was again thoroughly mixed and pulverized in a mortar, about 1000 kg / cm ² of wrestling with a diameter of about 1 cm, a thickness of about 1mm of the green compact pellets and without, which in 143 hours an electric furnace at 845 ° C., in air heated Fired. Analysis of the molar ratios of the constituent elements of the fired sample by ICAP (results normalized by the number of moles of Cu) B
i _1.98 , Pb _0.18 , Sr _2.00 , Ca _1.96 , Cu _3.60 .

The temperature change of the electric resistance is as shown in FIG. As is clear from this figure, the electrical resistance of this substance is
It began to fall from 120K, dropped sharply from 115K, and became zero at about 105K, confirming that this substance has extremely excellent superconducting properties.

In addition, as shown in FIG. 2, the measurement results of the Meissner effect confirmed that a superconductor was obtained at about 105 K or more.

Further, this material was a sintered body having sufficient mechanical strength for practical use.

Example 2 The same procedure was performed as in Example 1 except that the firing time at 845 ° C. was extended to 244 hours. The result of analyzing the composition of the fired sample by ICAP (the result of normalizing by the number of moles of Cu) is Bi _1.96 , Pb _0.10 , Sr _2.00 , Ca _1.94 , Cu
It was _3.60 .

The temperature change of the electric resistance of the substance obtained in this example is as shown in FIG. As is clear from this figure, the electric resistance of this substance began to fall from 115K, dropped sharply from 110K, and became zero at about 107K, confirming that this substance has extremely excellent superconducting properties.

Example 3 Ammonium oxalate was added to a mixed aqueous solution of nitrates of Bi, Pb, Sr, Ca, and Cu, and the composition ratio of component elements was Bi _1.92 , Pb
_{Oxalates of 0.48} , Sr _2.0 , Ca _2.0 and Cu _3.2 were precipitated,
After drying at 0 ° C and heating at 250 ° C, the mixture was heated in an electric furnace at 800 ° C for 24 hours in air to synthesize a black powder. This was reground and mixed, and pressed into a green compact having a diameter of 1 cm and a thickness of 1 mm with a press of about 1000 kg / cm ² and fired in air at 845 ° C. for 48 hours in an electric furnace. The result of analyzing this sample by ICAP (the result of normalizing by the number of moles of Cu) Bi _1.88 , Pb _0.20 , S
r _2.00 , Ca _1.96 and Cu _3.20 .

As shown in FIG. 4, the temperature change of the electric resistance sharply dropped from about 120K and became zero at about 105K. In addition, the Meissner effect and the mechanical strength of this substance showed substantially the same results as in Example 1.

Example 4 Ammonium oxalate was added to a mixed aqueous solution of respective nitrates of Bi, Pb, Sr, Ca, and Cu, and the composition ratio of component elements was Bi _1.92 , Pb
_{Oxalates of 0.48} , Sr _2.0 , Ca _2.0 and Cu _3.2 were precipitated,
After drying at 0 ° C and heating at 250 ° C, the mixture was heated in an electric furnace at 800 ° C for 24 hours in air to synthesize a black powder. This was re-crushed and mixed, and pressed into a compact having a diameter of 1 cm and a thickness of 1 mm with a press of about 1000 kg / cm ² to be fired and heated in air at 835 ° C. for 92 hours in an electric furnace. Analysis results of this sample by ICAP (results normalized by moles of Cu) Bi _1.82 , Pb _0.08 , S
r _2.00 , Ca _1.90 and Cu _3.20 .

As shown in FIG. 5, the temperature change of the electric resistance rapidly dropped from about 120K and became zero at about 107K. The X-ray diffraction pattern of this sample showed that the high-temperature phase was 90% or more as shown in FIG. The Meissner effect of this substance was confirmed to be about 95% or more in the high temperature phase as shown in FIG.

Example 5 Ammonium oxalate was added to a mixed aqueous solution of nitrates of Bi, Pb, Sr, Ca, and Cu, and the composition ratio of component elements was Bi _1.92 , Pb
_{Oxalates of 0.48} , Sr _2.0 , Ca _2.0 and Cu _3.2 were precipitated,
After drying at 0 ° C and heating at 250 ° C, the mixture was heated in an electric furnace at 800 ° C for 24 hours in air to synthesize a black powder. This was re-crushed and mixed, and pressed into a compact of 1 cm in diameter and 1 mm in thickness by a press of about 1000 kg / cm ² and fired in an electric furnace at 830 ° C. for 72 hours in the air. The result of analyzing this sample by ICAP (the result of normalizing by the number of moles of Cu) Bi _1.90 , Pb _0.20 , S
r _2.00 , Ca _1.96 and Cu _3.20 .

The temperature change of the electrical resistance of this one dropped sharply from about 120K and became zero at about 107K. Its X-ray diffraction pattern showed that the high-temperature phase was about 95% or more as shown in FIG. The Meissner effect of this substance showed substantially the same results as in Example 4.

Example 6 Ammonium oxalate was added to a mixed aqueous solution of respective nitrates of Bi, Pb, Sr, Ca, and Cu, and the composition ratio of the constituent elements was Bi _1.4 , Pb _0.6 ,
The oxalate of Sr _2.0 , Ca _2.0 , and Cu _3.6 was precipitated, dried at 100 ° C., heated at 250 ° C., and then heated in air in an electric furnace at 800 ° C. for 24 hours to synthesize a black powder. This is crushed and mixed.
As a green compact pellet having a diameter of 1 cm and a thickness of 1 mm with a press of 1000 kg / cm ² , this was heated and fired in air in an electric furnace at 845 ° C. for 150 hours. The result of analyzing this sample by ICAP (the result of normalizing by the number of moles of Cu) Bi _1.4 , Pb _0.09 , Sr _1.96 , C
a _1.90 and Cu _3.60 .

The temperature change of the electrical resistance of this one dropped sharply from about 120K and became zero at about 107K. As a result of X-ray diffraction and Meissner effect measurement, it was confirmed that the high-temperature phase was contained at about 95%.

〔The invention's effect〕

The Bi-Pb-Sr-Ca-Cu-O-based material according to the present invention is a superconducting material having a superconducting critical temperature at least at a liquid nitrogen boiling point of 77K or more and a critical temperature at a high temperature of 105K or more.

As described above, the method for producing this substance is easy. Particularly, in the case of the precipitation method, the reproducibility in the production method is high as described above, and the target substance having a high ratio of a high Tc phase is easily obtained.

[Brief description of the drawings]

FIG. 1 is an electric resistance-temperature correlation diagram of the substance obtained in Example 1, and FIG. 2 is a complex susceptibility-temperature correlation diagram of the substance. FIG. 3 is an electric resistance-temperature correlation diagram of the substance obtained in Example 2, and FIG. 4 is an electric resistance-temperature correlation diagram of the substance obtained in Example 3. FIG. 5 is an electric resistance-temperature correlation diagram of the substance obtained in Example 4,
FIG. 6 shows an X-ray diffraction diagram of the substance obtained in the example, and FIG. 7 shows a complex susceptibility-temperature correlation diagram of the substance obtained in the example. FIG. 8 is an X-ray diffraction diagram of the substance obtained in Example 5.

────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Naoichi Yamamoto 1-2 Satakedai, Suita-shi, Osaka Satakedai Heights D-17-203 (56) References JP-A-1-242421 (JP, A) JP-A-1-215721 (JP, A) JP-A-1-224229 (JP, A) JP-A-2-9721 (JP, A) JP-A-1-275433 (JP, A) JP, A) WO 89/7579 (WO, A1) (58) Fields investigated (Int. Cl. ⁶ , DB name) C01G 1/00-35/00 H01L 39/00-39/24 H01B 12/00

Claims (1)

(57) [Claims] 1. A Bi-Pb-Sr-Ca- Cu-O -based oxide, constituent elements of Bi oxide, Pb, Sr, Ca, is the ratio of the number of moles of Cu, Bi _n, Pb _m , Sr _x , Ca _y , Cu _z (n, m, x, y, z are 0.5 <n <2.6,
0.01 ≦ m ≦ 1.5,1.5 ≦ x ≦ 2.2,0.8 ≦ y ≦ 2.2,2.0 ≦ z ≦
4 which shows a value of 4), and has an electrical resistance of zero at 100 K or more, a Bi-Pb-Sr-Ca-Cu-O-based superconducting material.