JPS5938197B2 - Melt for growth of barium lead bismuthate single crystals - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a melt suitable for growing barium lead bismuthate single crystals, which are promising as materials for cryogenic devices.

Barium lead bismuthate (chemical formula: BaPb1 xBi
xC)s) is barium leadate (chemical formula: BaPbO5)
and barium bismuthate (chemical formula: BaB103), in the composition range of X from 0.05 to 0.35,
It is known to exhibit superconductivity.

Since this solid solution is an oxide, it is stable in an oxidizing atmosphere and is attracting much attention as a material for superconducting elements that can be produced by the same method as ordinary ceramics.

However, this barium lead bismuthate solid solution is easily decomposed at high temperatures, and therefore it is currently impossible to grow a single crystal from a molten state under normal pressure.

Therefore, a method of growing a single crystal using a high-temperature, high-pressure device has been considered, but the device must be extremely expensive, and this method is also virtually impossible.

For this reason, methods have been proposed in which single crystals are grown at low temperatures.

That is, the material for which a single crystal is to be grown (a sintered body of barium lead bismuthate) is dissolved in a solvent, and the molten material is slowly cooled or the solvent is evaporated to grow a crystal. This is the so-called flux method.

To use this method, you must first select a substance to serve as the solvent.

As this solvent, it is necessary to select a solvent that satisfies the following conditions: 1) It has a good understanding of the material used to grow the single crystal, 2) It does not introduce harmful impurities into the crystal, 2) It has an appropriate viscosity. However, the best such solvent must be found by examining a large amount of experimental data.

At present, no growth medium suitable for growing barium lead bismuthate single crystals is known, and therefore it has been impossible to produce barium lead bismuthate single crystals using this method.

An object of the present invention is to provide a melt that allows easy growth of barium lead bismuthate single crystals, which was previously impossible.

Briefly, the melt according to the invention is a melt for growing barium lead bismuthate single crystals, which is characterized in that it basically consists of barium oxide, bismuth oxide and an excess of lead oxide.

The melt according to the present invention has the advantage that a barium lead bismuthate single crystal, which was previously impossible to grow, can be easily grown with good controllability.

The present invention will be explained in more detail.

The barium lead bismuthate on which the single crystal is grown in the present invention is represented by the following general formula (1): % formula % (1) (where X is a real number smaller than 1), and in the present invention, Especially when X is 0
．． Although the present invention is directed to barium lead bismuthate, which is used as a material for superconducting elements and exhibits a value of 0.05 to 0.35, it is clear that the present invention is not limited to this.

The melt according to the present invention basically consists of barium oxide, bismuth oxide and excess lead oxide as described above, and it goes without saying that various additives may be added thereto.

The composition ratio of the melt when growing a barium lead bismuthate single crystal in the range of 0.05 <
Below, lead oxide is 60 to 90 (weight ratio).

This is because if the weight ratio deviates from this, there is a risk that the composition will deviate from the composition range of 0.05≦X≦0.35.

In order to grow barium lead bismuthate single crystals from such a molten material, the molten material kept in a molten state is slowly cooled, a single crystal is precipitated, and the remaining waste liquid is poured out, or an appropriate enquenching agent is used. This can be done by selectively removing the crystals and separating the waste liquid.

It is also possible to grow a single crystal by bringing a platinum wire or seed crystal into contact with the melt and pulling it up by rotation.Furthermore, it is possible to grow a single crystal thin film by bringing the melt into contact with a crystal substrate with good lattice matching. can also be grown.

That is, the method of growing a single crystal from a melt according to the present invention is basically not limited.

Examples of the present invention will be described below.

Example 1 First, barium carbonate, bismuth trioxide, and lead dioxide were each weighed so that BaO:Bi2O3:PbO2=15:15Nia0.

Next, the mixture was warm mixed, dehydrated, and dried, then loaded into a platinum crucible and heated in an electric furnace.

After being kept at a temperature of 1000'C for about 8 hours, the temperature of about 2°C/
It was slowly cooled at a rate of hr.

During this operation, BaO, Bi2O3, and lead oxide react to form and grow BaPb1-xBixO3 crystal nuclei.

When the temperature reached 800 to 850° C., the platinum crucible was tilted and the molten waste liquid (mainly composed of PbO) was transferred to another container.

As a result, BaPb was found inside the platinum crucible from which the waste liquid was poured out.
Only 1xBix03 crystals remained, and the thus grown crystals could be separated from the waste liquid.

Separation of the crystals and the waste liquid can also be achieved by cooling the platinum crucible containing the waste liquid to room temperature and then selectively removing only the waste liquid using an appropriate etching agent.

When the platinum crucible was removed from the electric furnace after growth, crystals of various shapes and sizes were found attached to the platinum crucible.

It was revealed by X-ray diffraction that most of the obtained crystals were single crystals, and their composition had an X of approximately 0.25.

Furthermore, when we measured the change in electrical resistance with temperature, we found that it showed a superconducting transition.

In this way, we were able to grow a single crystal of superconducting BaPb, xBix03, with a composition in which X was in the range of 0.05 to 0.35.

Example 2 Next, BaO:Bi2O3:PbO2=15:5:
A mixture having a composition ratio of 80 and 25:25:50 was dissolved and slowly cooled in the same manner as in Example 1.
In the former case, a single crystal having a composition of 0.15 in X was obtained, and in the latter case, a single crystal having a composition in X of 0.50 was obtained.

Thus, by changing the blending composition ratio of BaO, Bi2O3, and PbO2 toward the excess composition of PbO2, BaP
It has become clear that not only a single crystal of b1 xBix03 can be obtained, but also the composition of the obtained single crystal can be controlled.

In addition, by using excess PbO, a platinum wire was placed on top of the liquid.
Alternatively, the BaPb, xBixOa single crystal obtained by the above method is tied and fixed with a platinum wire as a seed, and superconducting BaPb is placed on the seed by pulling it up while rotating.
It was also possible to grow a single crystal of 1 x Bix03.

As described above, the present invention provides a novel method that enables single crystal growth of BaPb1 x Bix03, which has not been successful so far, and has the following advantages.

(1) Lead oxide, which also acts as a solvent due to its excessive amount, is B
Since it is a composition of aPb1 xBix03, there is no concern that impurities will be mixed into the growing crystal from the solvent, and a highly pure single crystal can be obtained.

(2) By changing the composition ratio of BaO, Bi2O3, and PbO□, a single crystal having a desired composition can be obtained.

Moreover, according to the melt of the present invention, BaP of various compositions can be used.
It has various advantages that are extremely effective not only for manufacturing high quality single crystals of b1 xBix03 but also for growing single crystal thin films on crystal substrates with good lattice matching.

Claims (1)

[Claims] 1. A melt for the growth of barium lead bismuthate single crystals, characterized in that it essentially consists of barium oxide, bismuth oxide and excess lead oxide.