JPH0274596A - Bismuth germanate single crystal and its manufacturing method - Google Patents

Abstract

PURPOSE:To prevent the generation of voids on the taking-up of the subject single crystal to contrive the improvement of the quality thereof by using GeO2 of a low temperature type containing that of a high temperature type in a content of <= a specific value in a method for producing the single crystal wherein the single crystal is taken up from the melted liquid of a mixture of Bi2O3 and GeO2 or a sintered product thereof. CONSTITUTION:A bismuth germanate single crystal (referred to as BGO) is obtained by Czochralski method from a melted mixture prepared by melting the powders of Bi2O3 and GeO2 or from the melted liquid of a mixed sintered product prepared by sintering the mixture of the Bi2O3 and the GeO2. In the method the GeO2 comprises essentially a low temperature type GeO2 wherein the content of a high temperature type GeO2 contained in the GeO2 is <=10wt.%. The generation of voids during the growth of the crystal is reduced, thereby providing the colorless and transparent BGO having a high light transmittance, containing no light-scattering substance and having a good quality.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a bismuth germanate single crystal and a method for producing the same, particularly for bismuth germanate, which is useful for optics and γ-ray scintillators. The present invention relates to a bismuth germanate single crystal and a method for producing the same.

[Prior Art] A bismuth germanate single crystal represented by the formula B i 4 Ge30+z is used for optics and γ-ray scintillators, and this crystal is similar to bismuth oxide (Bi203).
, produced by a single crystal pulling method using the Czochralski method from a melt of germanium dioxide (G e Os) powder. However, in the single crystal growth method using the Czochralski method, fluctuations in temperature at the solid-liquid interface of the growing crystal and fluctuations in the crystal growth rate occur due to the accumulation of impurities during the crystal growth process, which causes impurities to be incorporated into the crystal. When a liquid solidifies, band-like voids are generated due to density differences between the solid and liquid, and as these are incorporated into the crystal, these voids act as light scatterers, affecting the crystal quality of the resulting single crystal. This has the disadvantage of lowering the crystallization yield as well as lowering the crystallization yield.

Therefore, various methods have been proposed to prevent the occurrence of such voids, such as increasing the diameter of the growing crystal and protruding the solid-liquid interface of the crystal by setting the rotation speed of the seed crystal at 40 to 60 rpm during pulling. The ratio H/D with high H is -0,2
There is also a known method of flattening the solid-liquid interface to reduce the amount of voids within the range of ~0.2 (see Japanese Patent Publication No. 58-49517). It has the disadvantage that it is not possible to grow a long single crystal with a large size, and the occurrence of voids has not been completely solved.

[Structure of the Invention] The present invention relates to a bismuth germanate single crystal (hereinafter abbreviated as BGO) that solves these disadvantages, and a method for producing the same. When pulling a single crystal from the melt of a mixed fired body of germanium dioxide and germanium dioxide, the germanium dioxide should essentially consist of low-temperature germanium oxide, and the amount of high-temperature germanium oxide should be 10% by weight or less. A bismuth germanate single crystal (Bi, Ge) is added to a mixed melt of bismuth oxide and bismuth oxide or a mixed fired product of bismuth oxide and germanium dioxide.

The method is characterized in that a seed crystal of 012) is immersed and then raised while rotating to obtain a single crystal rod.

That is, the present inventors investigated various ways to prevent the generation of voids during pulling of a single crystal of B i 4 Ge* 012 using the Czochralski method.
O□) From the mixed melt obtained by melting the powders or from the melt of the mixed fired body obtained by mixing bismuth oxide powder and germanium dioxide powder and firing this at 700 to 1.000 ° C. In the method for obtaining BGO using the Ralski method, if the germanium dioxide is essentially composed of low-temperature germanium oxide and the amount of high-temperature germanium oxide contained therein is 10% by weight or less, crystal growth is possible. We have discovered that it is possible to obtain high-quality BGO that has high light transmittance and does not contain scatterers because the occurrence of voids in the BGO is reduced.
GO is essentially composed of 2B ia Ge3012 as its main component, which constitutes 70% by weight or more.
Since the content of i12GeO□0 is 3.0% by weight or less, the present invention was completed by confirming that a colorless and transparent material with few voids could be obtained.

This will be explained in further detail below.

As described above, the present invention uses BGO from a melt of a mixed melt of bismuth oxide and germanium dioxide or a mixed sintered body of bismuth oxide and germanium dioxide using the Czochralski method.
Basically, this method can be carried out according to a known method.

Therefore, bismuth oxide (Bi203), germanium dioxide (Ge
Oz) should be as pure as possible, and therefore preferably have a purity of 99.99% or higher; Bismuth oxide (BizOs) and germanium dioxide (pulverized to 50 μm or less)
GeOz) may be mixed in equivalent amounts and heated to 1,050°C or higher to form a mixed melt.
It may be fired at 00°C to form a mixed fired body, and then heated to 050°C or higher to form a melt. In addition, from this melt, B
The seed crystal used for pulling GO may be about 5 mm x 5 mm cut from a single crystal of BGO obtained by a conventional method.

However, the method of the present invention requires that the germanium dioxide used here essentially consist of low-temperature germanium, and that the content of high-temperature germanium is 10% by weight or less. In other words, this germanium oxide has a thermal transition point of 1,033°C,
It has a melting point of 1,116°C and a red-eye crystal structure (
It is known that there are two types: a low-temperature type that is 3□) and water-soluble, and a high-temperature type that has a melting point of 1°086°C and a rutile crystal structure (64) and is insoluble in water. Ori,
Normally, these elements are mixed together, but according to experiments conducted by the present inventors, when germanium dioxide is melted together with bismuth oxide and BGo is pulled from this melt, germanium dioxide is mixed with high-temperature germanium oxide. If it is contained in a large amount, voids will occur, but it has been found that if it is made mainly of low-temperature germanium oxide, no voids will occur, so the germanium dioxide used here must consist essentially of low-temperature germanium oxide, and the amount of high-temperature germanium oxide must be 10% by weight or less; in fact, this reduces the occurrence of voids during single crystal pulling. Therefore, the advantage is that BGO of good quality can be easily obtained.

Moreover, BGO obtained by the method of the present invention has the formula B i 4
The main component is bismuth germanate represented by Ge30+z, but if the germanium dioxide used here contains a large amount of high-temperature germanium oxide, the resulting BGO will have a large amount of voids and , formula Bi+zGeO□. It contains bismuth germanate shown by, and this gives it a yellow or red color, so from this point of view as well, germanium dioxide is preferably one whose main component is low-temperature germanium oxide.

Next, examples of the present invention will be given. The content of high-temperature germanium oxide in the germanium dioxide used in the examples is the value measured by the following method, and the evaluation method for the obtained BGO crystals is The results are shown below.

(Method for measuring the amount of high-temperature G e OZ in G e O2) When germanium dioxide (GeOz) is heated and melted in concentrated hydrochloric acid, the low-temperature germanium oxide dissolves and the high-temperature germanium oxide becomes an undissolved residue, so Q e O2 was heated and melted in concentrated hydrochloric acid, the weight of the undissolved residue at that time was determined, and the ratio (%) to the weight before treatment was determined.

(Evaluation method of BGO residue) 30.Evaluation is based on how many product blocks of OO x 30.0 OX 50.00 mm are cut out, but in this case, there are no void-like inclusions in more than half of the 30.0 OX 30.00 mm plane. I decided to do so.

Moreover, this evaluation is shown in Table 1. In addition, the crystal evaluation in the table was evaluated based on the state of appearance and the amount of voids.

Examples 1-5. Comparative Example 1 Bismuth oxide (Bi203) with a purity of 99.999% and an average particle size of 50 μm and six types of germanium dioxide (GeOz) with high-temperature germanium oxide contents shown in Table 1 were used. BGO was mixed in an amount of 32 kg, placed in a platinum crucible with a diameter of 200 mm and a depth of 200 mm, and heated to 1,070'C using high frequency induction heating to melt it.

Next, 5 mm x 5 mm of B 14 Ges was added to this mixed melt.
B 14G e 3012 with a crystal diameter of 110 mm is immersed in an O+□ seed crystal and pulled up at a speed of 0.5 to 3 mm/hour.
When a single crystal rod (12.5 kg) was pulled up and the obtained single crystal was evaluated, the results shown in Table 1 were obtained.

Moreover, as a result of X-ray diffraction, the samples of Examples 1 to 5 all had Bi4Ge3012 as the main component. A trace amount of 8112G e O□ below 0%. was found, but Comparative Example 1
The sample of B i 12 in B ia Ge3012
It was found that 5% or more of G e O20 was present.

Claims (1)

[Claims] 1. A mixed melt of bismuth oxide and germanium dioxide;
Alternatively, when pulling a single crystal from a melt of a fired mixed body of bismuth oxide and germanium dioxide, the germanium dioxide is essentially composed of low-temperature germanium oxide, and the amount of high-temperature germanium oxide is 10% by weight or less. A method for producing a bismuth germanate single crystal, characterized in that the single crystal is obtained by pulling it from a mixed melt of bismuth germanate and bismuth oxide or from a melt of a mixed sintered product thereof. 2. Bismuth germanate single crystal is mainly Bi_4
Consists of Ge_3O_1_270% by weight, Bi_1_2
A bismuth germanate single crystal characterized in that GeO_2_0 is 3.0% by weight or less.