JPH01131048A - Superconducting porcelain composition - Google Patents

Abstract

PURPOSE:To drop a calcination temperature and to improve calcination density and critical current density without leading to reduction in critical temperature in a superconducting porcelain composition of Y-Ba-Cu-O base, by partially replacing part of copper with a specific amount of lead. CONSTITUTION:This superconducting porcelain composition has a composition shown by the formula (R is rare earth element including Y or Sc; 6<=y<=0; 0.02<x<2.8). The superconducting porcelain composition is obtained by blending raw materials such as BaO, Y2O3, CuO and PbO in a given ratio, calcining, molding and burning. Since copper of the superconducting porcelain composition is partially replaced with a specific amount of lead, the composition can be burnt at a relatively low temperature and yet calcination temperature and critical current density can be improved.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a superconducting ceramic composition, and more specifically, a superconducting ceramic composition that has both a high critical temperature (Tc) and a high critical current density (Tc) and can be fired at a low temperature. This invention relates to a novel superconducting ceramic composition.

[Prior Art] In February 1987, Y-Ba-Cu-0 based oxide superconducting porcelain having a critical temperature of 90°C, which exceeds the boiling point of liquid nitrogen, was discovered by Chew et al. of Hughston University in the United States.

However, Y-Ba-Cu-0 based oxide porcelain has poor sintering properties, and can only be produced with a porous structure using normal firing methods. For this reason, the contact area between the particles constituting the sintered body is small, and as a result, there is a drawback that the critical current density cannot be obtained very high.

Generally, to densify a sintered body, (1) Increase the firing temperature.

(2) Add a sintering aid.

However, in the case of Y-Ba-Cu-0 ceramics, in method (1), Y
Ba2Cu307-z (0<z<1) decomposes, the crystal grains become larger, but the critical temperature decreases, and B
It is not possible to raise the firing temperature because the volatilization of components such as aCuO2 causes a shift in composition and a decrease in density.

For the addition of the auxiliary agent (2), additives that promote mass transfer by creating a liquid phase at the grain boundaries are generally selected, but if this additive remains at the grain boundaries, there will be no movement between the grains. The superconducting phase becomes sandwiched, causing a significant decrease in critical current density and critical temperature. Therefore, it is difficult to use the method of adding a sintering aid.

The above problems are not limited to Y-Ba-Cu-0 porcelain, but also Sc
Systems in which Ba is replaced with rare earth elements, including Sr.
There still exist general oxide superconducting ceramics with other compositions substituted with elements such as.

[Problems to be Solved by the Invention] The present invention aims to solve the problem of low critical current density caused by difficulty in sintering, which the conventional compositions have.

[Means for solving the problems 1 The present inventors have overcome the above problems of R-Ba-Cu-0 based oxide superconductors (R is a rare earth element including Y and Sc; the same applies hereinafter). As a result of extensive research, it was discovered that by replacing a portion of Cu, one of the components, with a limited amount of PB, a superconducting material with a high critical temperature, good sinterability, and high critical current density could be obtained. The present invention was achieved by discovering that

[Function] The superconducting ceramic composition according to the present invention can be synthesized by any of the generally known synthesis methods, such as an in-phase reaction method, a spray drying method, and a coprecipitation method. Further, a thin film can also be synthesized by applying methods such as sputtering and CVD (chemical vapor decomposition).

Here, the oxygen amount y in the above-mentioned formula is an amount that changes depending on the lead amount X and firing conditions such as the firing atmosphere and cooling rate.

An example in which the in-phase reaction method is applied and yttrium (Y) is used as R will be described in detail below.

The raw material includes, for example, barium oxide (Bad).

Yttrium oxide (Y203), cupric oxide (Cub)
, - Lead oxide (PbO) is used and mixed in a predetermined ratio wet or dry.

Any of the raw materials that can be thermally decomposed to become barium oxide, lead oxide, yttrium oxide, or copper oxide can be used as a substitute for the above-mentioned raw materials.

That is, barium carbonate (BaC) is used instead of barium oxide.
O3), barium peroxide (Ba02).

Barium oxalate (BaC20+) can be used, and yttrium oxalate (Y2+) can be used instead of yttrium oxide.
(C204) 3), yttrium carbonate (Y2 (CO
a) 3) etc. can be used, and instead of cupric oxide, basic copper carbonate (Cu(OH)2・CuC03), copper hydroxide (
Cu(OH)2) etc. can also be used, and instead of lead oxide, lead tetroxide (pb304), lead dioxide (pbo2),
Basic lead carbonate (Pb(OH)2.PbC03) is also used.

It is desirable that these alternative raw materials be appropriately selected in consideration of the reactivity, purity, etc. of the powder.

The mixed powder is calcined as a powder at a temperature of 700°C or more and 100°C or less, preferably 800°C or more and 950°C or less. If the calcination temperature is too high, the entire product will melt, so care must be taken. Furthermore, if the calcination temperature is too low, the solid phase reaction will not proceed sufficiently, making it impossible to obtain a burnt and dense sample.

The calcining temperature at this time needs to be lower as the lead content increases. For example, the optimum calcination temperature for lead-free samples is between 900°C and 1000°C;
For samples with lead content X of 1, the temperature is 850°C to 900°C,
For the sample where x is 2, the temperature is 800°C to 850°C.

The calcined powder has changed to a superconducting phase, but since it has aggregated into coarse particles, it is preferably ground again using a ball mill, a jet mill, or the like. The important thing to keep in mind here is that if water is used during pulverization, a reaction will occur between the sample and the water, which will generate heat and decompose. Therefore, it must be dry-pulverized or a non-aqueous dispersion medium must be used.

After granulating the powder produced as described above, it is press-molded or packed into a metal tube and drawn. This is fired in oxygen or air to produce a superconducting ceramic composition.

The firing temperature is significantly lowered by the effect of lead addition, and the firing temperature to obtain samples with the same relative density (the apparent ratio of density to the density without voids) is significantly lower than for samples without lead. Become. When X is 0.02 or less, the effect of reducing the firing temperature and improving the critical current density is insufficient, and the decrease in the firing temperature becomes more noticeable as X increases, but when X is 2.8 or more, the critical temperature decreases. do.

Although the solid phase reaction method has been explained above, it can also be produced by other powder synthesis methods such as coprecipitation method and spray drying method. For example, a water-soluble salt such as acetate or nitrate can be used to prepare a uniform mixed aqueous solution of component elements for spray drying or coprecipitation. It is known that the sintering temperature of powder produced by the coprecipitation method is lower than that of powder produced by the oxide solid-phase reaction method. By doing so, the effect of further lowering the sintering temperature can be achieved.

The composition of the present invention can be made not only into a bulk sintered body but also into a thin film by a sputtering method or a CVD method.

The effects of the new composition have been explained above mainly from the viewpoint of lowering the sintering temperature, but there are other effects of great practical significance, such as increasing the density of the sintered body and increasing the critical temperature. Although the detailed mechanism of the density increase is unknown, it is thought that PbO with a low melting point is generated in the liquid phase during the reaction process, and the density increase is caused by the mechanism of liquid phase sintering.

As a result of high density, the electrical properties, especially the critical current density (Jc
), and the relative density of the sample with the conventional composition was 60~
80% and Jc was about 300 to 400 A/cm2, whereas the composition of the present invention had a relative density of 85 to 98
%, and Jc was also significantly improved to 500 to 3400 A/crn''.

[Example] Cupric oxide, yttrium oxide, -lead oxide, and barium carbonate were blended in a predetermined ratio and wet-mixed in a ball mill using 2-propertool as a dispersion medium. After drying the kneaded powder, it was calcined at a temperature in the range of 800°C to 950°C, and pulverized with a jet mill to an average particle size of about 1LLm.

2% by weight of polyvinyl butyral was added as a binder to this powder, and after granulation, it was 3 x 3 x
It was molded into a 30 mm rod shape, degreased, and then fired in the air at the temperatures shown in Table 1 for 8 hours.

Table 1 shows the results of measuring the relative density and superconducting properties of samples with various lead content X. As is clear from the table, the relative density and critical current density were greatly improved by replacing copper with lead, and the critical temperature was also slightly increased.

After measuring and pulverizing these samples, we identified the formed phase using powder X-ray analysis, and found that it was almost a single phase, and the peak position was close to YBa2CuaO7, indicating that the pb atoms were completely substituted and solidified at the Cu site. It was found that it was dissolved.

As a result of testing in the same manner as above using rare earth elements including Sc instead of yttrium, almost the same results as in the case of using yttrium were obtained.

Notes to Table 1) *: Comparative example **: Measured values at liquid nitrogen temperature [Effects of the invention] As described above, the replacement of copper with lead does not lower the critical temperature and (1) lowers the firing temperature. It has the effects of reducing (2) increasing sintered density and (3) increasing critical current density, and can be used as a material to overcome the problems of conventional oxide-based superconductors such as high temperature synthesis, low density, and low critical current density. , has great industrial value.

Claims (1)

[Claims] 1. General formula RBa_2Pb_xCu_3_-_xO_y, where R is a rare earth element including Y and Sc, and when expressed as 6≦y≦9, it has a composition of 0.02<x<2.8. Superconducting porcelain composition.