JPH01192760A - Ag2o3-containing oxide superconductor and production thereof - Google Patents

Abstract

PURPOSE:To improve sintering density, critical current density and processing properties, to improve and to stabilize critical temperature, to uniform crystal structure and to make composition uniform, by containing specific oxide crystal grain and Ag solid solution obtained from Ag2O3 as a starting raw material arranged at least in the vicinity of grain boundary of the crystal grain. CONSTITUTION:A given amount of powder of starting raw materials (e.g., Y2O3, BaCO3 or CuO) in order to form L-B-Cu-O oxide crystal grain (L is lanthanide element including Y; B is one or more elements selected from Ba, Sr and Ca) is ground, calcined at, e.g., about 900 deg.C for 5 hours to give powder, which is press molded. Then the pressed material is sintered in an O2 atmosphere at 900-950 deg.C for, e.g., about 10 hours and ground to give first sintered powder. The first sintered powder is blended with Ag2O3 powder in the atomic ratio to satisfy the relationship shown by the formula (x is 0.07-0.7), packed with a sheath agent, molded and processed to give a molded article, which is partially melted and sintered in an O2 atmosphere at, e.g., 950-1,050 deg.C for about 10 hours to give a second sintered material. Then the second sintered material is annealed at 50-100 deg.C/hour cooling rate.

Description

[Detailed description of the invention] [Industrial application field] The present invention uses Y and Ln (lanthanoid) series and Ba.

The present invention relates to an oxygen-deficient triple-structure perovskite plasticized Bt conductor consisting of Cu and O, and particularly to a homogeneous Ag-containing oxide superconductor with good workability and sinterability, and a method for producing the same.

[Prior art] Generally, Y and Ln (lanthanide) systems and Ba.

An oxide superconductor made of Cu and O is a material widely known as a lobskite having an oxygen-deficient triple structure. Since this material is an oxide, it has no elasticity and no plastic deformability.

[Problem that the invention seeks to solve]

Therefore, even if conventional superconductor materials are rolled, drawn, drawn, or extruded during wire processing, the crystals themselves do not have the ability to plastically deform, so adhesion and fusion at grain boundaries are difficult to occur. It is in. Moreover, the surface of the grain boundary has the characteristic that oxygen can easily enter and exit, and elements such as oxygen can easily diffuse therethrough. Therefore, in the case of polycrystalline materials, grain boundaries are formed by impurities, Ln (Y), Bat Cu* 0y
Diffusion is actively occurring, with elements that deviate from the stoichiometric composition, such as -y, gathering together. In addition, the □ oxide absorbs and releases oxygen as the temperature rises and falls, as if it were breathing. As a result, as the oxygen content decreased, a decrease in Tc (critical temperature) and a change in crystalline waterfall occurred.

Therefore, supplying a large amount of oxide is a condition for producing a high quality superconductor. Therefore, systems for supplying a large amount of oxygen have been studied, especially for wire rods.

In view of the above-mentioned drawbacks, the technical problem of the present invention is to provide a sintered body that controls oxygen supply to the oxide, imparts plastic deformability, has good workability and sinterability, and An object of the present invention is to provide a homogeneous pore-free oxide superconductor and a method for producing the same.

[Summary of the Invention] For Ln(Y)BaCuO-based oxide superconductors, control of oxygen constituting the oxide is very important. The oxygen content is determined by the crystal structure of the superconductor and the superelectric properties (Tc, x
) is almost determined. Therefore, when processed into a wire rod, there are problems such as a decrease in the amount of oxygen, a lack of plastic deformability as a characteristic of oxides, and the occurrence of microcracks and a decrease in Jc (critical current density). There is.

Therefore, in the present invention, the oxygen content was controlled and supplied by adding Ag2Oi (silver peroxide) powder.

The effect of adding Ag is explained in Japanese Journal
ofapplied physics vol, 26
No. 5 Hay 1987 PPL832-833 explains that T due to the substitution effect of CuO and Ag2O
The electrical resistance disappears steeply near c, and furthermore Ag is reduced to C.
It has been reported that there is no significant change in Tc even after 50% substitution with u.

The present invention is characterized by adding Ag 202.

In other words, when the sintering temperature of these Ln (Y) BaCuO systems is raised to 950° C. or higher, a portion of the materials starts to melt. This partially melted sample releases oxygen, oxygen vacancies progress, and the crystal structure transforms from orthorhombic to tetragonal. At this time, oxygen usually diffuses out between the oxide, which is outside the oxide, and the sheath material. Therefore, in the present invention, as described above, by adding A g 202, Agio
It releases oxygen from step 2 to make the space over-oxygenated, prevents the release of oxygen elements to the outside of the oxygen substance, and also adsorbs oxygen when melting.
It is designed to release oxygen during solidification.

Here, the general properties of Ag will be explained.

Silver is generally produced as a sulfide and is produced in the form of bright silverite (Ag□S).
), dark silver ore (3Ag*S.

AgtSs), brittle silver ore (5Ag2S-3bi Si)
etc. are known. A considerable amount of silver is also obtained as a by-product during metal refining of copper and zinc.

In addition, silver is a silver-white, shiny metal, and in its molten state, it absorbs a large amount of oxygen (O□20.28 ml/1 ml A).
It absorbs oxygen (g at 973°C), releases occluded oxygen during solidification, and causes the 5hittina (splatter) phenomenon.It has the highest electrical and thermal conductivity among metals, and is second only to gold in malleability.

Chemically stable to water and oxygen, but produces black silver peroxide when exposed to ozone. N2°N2. It does not react with C even at high temperatures, but it easily reacts with Alogen and sulfur. It is not attacked by non-oxidizing acids such as hydrochloric acid, but
Soluble in nitric acid and well in hot sulfuric acid.

Because of the above properties, Ag, silver oxide, and silver peroxide are relatively stable, and by adding Ag and 202 together with the oxide superconductor, oxygen adsorption and release can be controlled, and Ln ( Y) It is possible to supply a sufficient amount of oxygen to BaCuO.

Furthermore, Ag2O2 powder can be easily mixed homogeneously by making the crushed powder of the sintered body fine.
When Ag2o2 and YBaCuO mixed powder are press-molded and sintered, mutual diffusion occurs between Ag2o2 and YBaCuO powder, improving the sintered density, expanding crystal grains, and making the crystal structure uniform.

Furthermore, when the Ag2o2 powder and YBaCuO mixed powder is sealed in a sheath material such as Ag or Ag alloy and subjected to plastic processing such as rolling or wire drawing, the sinterability is improved compared to one that does not contain AgxO2. However, a more homogeneous oxide can be produced.

The reason for the above effects can be explained as follows.

Ln(Y)BaCuO powder sintered in oxygen generally occludes oxygen sufficiently. This Ln (Y)Ba
A characteristic of CuO powder is that it releases oxygen at 550°C or higher when heated from room temperature.
It has the property of absorbing oxygen when cooled from ℃ to about 550℃. Further, the property of Ag202 is that it is produced by ozone oxidation at room temperature, so it bonds with oxygen in a supersaturated state. Therefore, when these Ln (Y) BaCuO powders and Agxot are mixed, press-molded, sealed in a sheath material, and heated, Ag
202 releases oxygen and begins to melt again. molten Ag
can store large amounts of oxygen. At that time, YBa
Oxygen released from CuO is stored and incorporated into molten Ag. Moreover, this molten Ag is surrounded by Ln(Y)BaCu
Ln(Y)BaCuAgO-containing CuAg by reacting with O,
Contains a large amount of oxygen. During solidification, molten Ag releases oxygen, and the released oxygen is absorbed by the Ln(Y)BaCuAgO system as it cools.

Furthermore, oxygen that diffuses and enters through the Ag sheath material will be supplied to the Ln (Y) BaCuAgO system, and oxygen will dissociate from the stoichiometric ratio 'W' + Ba2 (Cu, Ag)s Oa, * There is no generation of foreign phases caused by this, and it exhibits good superconducting properties (Tc,
The effect of adding O2 is very large.

Of course, in the case of a bulk material, since there is Ag dissociated from Ag202, it does not become porous, and the sintered density improves, resulting in less easy cracking and improved workability.

As described above, in the present invention, AFK202 is Ln (Y)B
By mixing it with aCuO-based oxide superconductor, Ln (
Y) Improved sinterability of BaCuO powder and improved workability by homogenizing the bulk sintered body. Furthermore, Ag
By adding 202, oxygen element is sufficiently added to Ln(Y)Ba
Since it can be supplied to CuO, it exhibits good superconducting properties (Tc, x) and Jc due to the stabilization of the crystal structure, and is a very useful method in the application of oxide superconductors.

That is, the present invention provides Ln(Y)BaCuO based oxide with A
By adding glow (silver peroxide), pure Ag liberated from Ag*02 can be used as an oxygen source for oxides.
n (Y) BaC'uO is diffused and substituted as a solid solution, so that the processability and sinterability of the oxide superconductor are good, and the sintered body becomes a homogeneous oxide superconductor without voids. This is what I did.

The manufacturing method involves mixing unstable silver peroxide with Ln(Y)BaCuO-based sintered powder and pulverizing it.
The produced powder is sintered and packed into a sheath material and sintered, and as the temperature rises, oxygen is released from AgzO2 and oxygen is supplied to Ln(Y)BaCuO. Furthermore, by diffusing the free Ag element into the matrix,
It has improved workability and sinterability, has a homogeneous structure, and has good superconducting properties.

[Means for Solving the Problems] According to the present invention, L-B-Cu-0 oxide crystal grains (where L is a lanthanoid element containing Y, B is Ba, Sr
represents at least one or more elements selected from the group consisting of An AgxOx-containing oxide superconductor is obtained.

Furthermore, according to the present invention, L-B-Cu-0 oxide crystal grains (where L is a lanthanoid element containing Y, B is Ba
, representing at least one element selected from the group consisting of Sr and Ca); a calcination step of producing a calcined powder; a second pulverization step of pulverizing the calcined powder to produce a pressing powder; a pressing step of press-molding the pressing powder to produce a pressed body; a first sintering step of sintering the pressed body in an oxygen atmosphere to produce a first sintered body;
a third pulverizing step of pulverizing the sintered body, an addition step of adding Ag2O2 powder to the pulverized first sintered body powder, and a first sintered body powder to which the Ag2Ot powder is added. ,
a forming step in which the sheath material is filled and then shaped; a second sintering step in which the formed object is sintered in an oxygen atmosphere to produce a second sintered body; and the second sintered object. A method for manufacturing an oxide superconductor containing Agio2 is obtained, which is characterized by comprising a slow cooling step of slowly cooling the Agio2-containing oxide superconductor.

[Example] Next, an example of the A g *02-containing oxide superconductor according to the present invention will be described.

FIG. 1 shows the manufacturing process of an oxide superconductor in which Agx Ot powder is added to a YBaCuO system. First, Y20s,
Prepare powder raw materials such as B aCOs and Cu 2 O, and pulverize them finely using a mortar or other method.

After that, perform calcination in air at 900°C for 5 hours.
The baked powder is crushed again (■), then molded into a shape that is easy to sinter (■), and heated at 900 to 1000℃ x 10 hours (
After that, the sintered body is sintered in a furnace (50 ~ Silver) powder in atomic ratio, x = 0.01 to 0.7, (Y
+ Bat (Cut-x Agx)s 07-y
), mix evenly and thoroughly rub ■,
After that, after filling into the sheath material and processing and molding, 950~10
Partially melted and sintered with 5G'Cx 10 hr (in oxygen) 11. At that time, during the heating process Ag2
Although 02 releases oxygen, the surroundings are sealed in the sheath material, and since it is common to use a material that hardly reacts with oxygen, the sheath material becomes supersaturated with oxygen. These supersaturated oxygens are absorbed by the silver, which partially melts at 950-1050°C. Furthermore, this silver can also store a large amount of oxygen generated and released from oxides. Therefore, since the silver diffused into the oxide and the silver that has been dispersed through the grains contains oxygen, it acts as an oxygen supply source during the diffusion of oxygen into the oxide during cooling, and provides sufficient oxygen. Samples manufactured by 0 or more processes that can be supplied are Tc, x
, ρ, structure, and composition analysis, etc. The zero composition ratio subjected to each 11111I constant is Y 20 s in atomic ratio.

Using powder raw materials of BaCo5, Cub, and Agt, the ratio of Y: Ba: (Cu + Ag) = 1: 2: 3 is a typical composition close to Tc - 90°.

FIGS. 2(a) and 2(b) show photographs of the fracture surface structure of the YBaCuO system having the above composition ratio. This sandal is Y+ Baz Cus 07-F sintered at 900°C and represents a typical oxide superconductor structure.

As can be seen from this photograph, the structure of YBaCuO consists of crystal grains of several μm in size, and spaces can be seen between the crystal grains.

For this reason, the superelectric properties Tc and x are not much different compared to single crystals, but Lc is 1/103 due to the grain boundaries.
It is very small in size, and has a porous chemical stability, so impurities and elements that deviate from the stoichiometric ratio tend to accumulate at grain boundaries, resulting in a composition and crystal structure that are susceptible to deterioration due to insufficient diffusion. .

The sample produced according to the present invention has improved sinterability and superelectric properties Tc and x due to the effect of adding Ag2O powder, and has a non-porous and dense structure.

Figure 3 shows a typical example of temperature change in electrical resistance.
The composition is Y+ Bat (Cua, a Ago, 2)s 0t
-y.

The electrical resistance on the vertical axis is measured using the 4-terminal method, and the measurement conditions are a current value of 100 nA and a resolution of voltage measurement of 1 x 10-'
It is V. Sample temperature was measured using an 81 semiconductor thermometer. The sample was first immersed in liquid nitrogen and measured at 77°, and then due to natural temperature rise, the electrical resistance became zero around 99° as shown in Figure 3, indicating that it was a superconductor. There is. In addition, the electrical resistance increases linearly as the temperature rises in a temperature range of 99° or higher, indicating the nature of temperature changes in metallic electrical conductors.

Figure 4 shows an example of the temperature change in electrical resistance near Tc (critical temperature) of the Y B a Cu A g O system.
0%), Tcm (lid port Tc: 50% of the resistance), and Tce (end point Tc: 90% of the resistance).

FIG. 5 shows Tco and Tcm defined in FIG.

For T c e, A g 20□ content is '1' +
The results are shown when X of Ba2(CuI-gAgx)i07-y was varied from 0 to 0.6. This sample is a partially melted sample. x=
There is no major change in Tc up to around 0.4, but x
=0.6, Tc is significantly reduced. Also, x=0.
1 composition is between Tco and Tce, that is, 10 to 90%
The temperature range of ΔT=0.9° is significantly reduced compared to ΔT=4° for X=0.

This is because the addition of A g 20□ powder improves sinterability, supplies sufficient oxygen, improves compositional heterogeneity, and makes the structure uniform.
The addition of xO2 is effective in improving sinterability and superconducting properties, especially in improving ΔT and Jc.

FIG. 6 shows the measurement results of Jc of Y+ Ba2(Cul-x Agt)s 07-F. It can be seen that as more A g 202 is added, Jc is significantly improved. Jc is A
The content of g202 increases to x=0.4, but when x=0.
5, there is a sharp decline. This is due to the decrease in Tc shown in FIG. Of course, when x=0.6, Tc is less than 77° and Jc cannot be measured.

From the above, it was confirmed that Jc improved as the content of Ag202 increased. Of course, Y is Ln (lanthanoid) La, Ce, Pr, Nd, Pm.

Sm, Eu, Gd, Td, Dy, Ho, Er.

It goes without saying that the same effect can be obtained by replacing Tm, Yb, Lu, or Ba with Sr, Ca, or the like.

Based on the above results, the composition range when adding the Agi 02 powder of this patent was limited to x=0.01 to 0.7.

When Agt0.2 is x<0.01, there is no effect on improving Jc and workability, and when Ag2o2 is x>0.7 or more, superconductivity is not exhibited, so the range was limited.

Of course, it is obvious that the present invention can also be applied to room-temperature superconductors having Tc near room temperature.

[Effect of the invention] As described above, according to the present invention, Ln(Y)Ba
t (Cut-xAgt) sow-y Ag20t
By adding the content of x=o, from 01 to 0.7,
The present invention has improved sintered density, stabilized Tc, reduced ΔT, improved Jc, uniformed crystal structure, and homogenized composition.The present invention provides an oxide superconductor with high Jc and good workability. It became possible to fabricate it and apply it to wire rods.

4. Detailed explanation of the invention Figure 1 shows Y Ba Cu O+Ag*O* powder 3
The diagram shows Y+ B at (Cu o, a Ago, *
) s 0y-y electrical resistance temperature change correlation diagram, Figure 4 is YHBa2 (Cuo, t Ago, s ) v O?
Figure 5 shows the temperature change correlation diagram of electrical resistance of −y.
) T co of s 07-F.

A g 202 content dependence correlation diagram of Tcm and Tce,
Figure 6 is Y+ Bat (Cul-K Agg)
Critical temperature Jc (A
/aJ) is a correlation diagram.

Figure 4 Figure 5 Ag(x)

Claims (5)

[Claims] 1. L-B-Cu-O oxide crystal grains (here, L represents a lanthanoid element including Y, and B represents at least one element selected from the group consisting of Ba, Sr, and Ca), and Ag_2O_2 Contains an Ag solid solution using as a starting material,
An Ag_2O_2-containing oxide superconductor, wherein the Ag solid solution is arranged at least near grain boundaries of the oxide crystal grains. 2. In the Ag_2O_2-containing oxide superconductor according to the first claim, the Ag_2O_2 is expressed by the formula L_0_.
_5～_1_. _5-Ba_1_. _0～_3_. ＿0
-(Cu_1_-_x-Ag_x)_1_. _5～_4
＿． _0-O_b_a_l (where x=0.01~0
．． It is 7. ) in a substantially satisfying atomic ratio. 3. Generate L-B-Cu-O oxide crystal grains (where L represents a lanthanoid element including Y, and B represents at least one element selected from the group consisting of Ba, Sr, and Ca). a first pulverizing step of pulverizing a starting raw material powder for use in the production process; a calcination step of calcination of the pulverized starting material powder to produce a calcined powder; and a calcination step of pulverizing the calcined powder to produce a powder for pressing. a second pulverizing step to produce a pressed powder, a pressing step to press-form the pressing powder to produce a pressed body, and a first sintered body to be produced by sintering the pressed body in an oxygen atmosphere. 1 sintering step, a third pulverizing step of pulverizing the first sintered body, an addition step of adding Ag_2O_2 powder to the pulverized first sintered body powder, and the Ag_2O_2 powder.
A molding process in which a first sintered body powder containing 2O_2 powder is filled into a sheath material and then shaped, and a second sintered body is produced by sintering the molded body in an oxygen atmosphere. 1. A method for manufacturing an oxide superconductor containing Ag_2O_2, comprising a sintering step of step 2 and an annealing step of annealing the second sintered body. 4. In the method for manufacturing an Ag_2O_2-containing oxide superconductor according to the third claim, the amount of Ag fine particles added in the addition step is determined by the formula: L_0_. _5～_1_. _5-Ba_1_. ＿0〜＿
3__. _0-(Cu_1_-_x-Ag_■)_1_.
_5～_4_. _0-O_b_a_l (However, x=0.
07 to 0.7. ) is added with an atomic ratio that satisfies
g_2O_2 oxide superconductor manufacturing method. 5. In the method for producing an oxide superconductor containing Ag_2O_2 according to claim 3, the second sintering step includes partially melting and sintering at a sintering temperature of substantially 950 to 1050°C. A method for producing an oxide superconductor containing Ag_2O_2, characterized in that: