JP2823741B2 - Method for producing bismuth germanate single crystal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a bismuth germanate single crystal, and more particularly to a method for producing a bismuth germanate single crystal which is useful for optics and X-ray scintillators.

[0002]

2. Description of the Related Art A single crystal of bismuth germanate (hereinafter abbreviated as BGO crystal) used as a scintillator is required to have a large amount of light emission. Has the disadvantage that the luminescence is reduced (K. Takagi et al., J. Cryst.
Growth 52 (1981), 584).

Although the cause of this crystal defect is not yet clear, since the presence of impurities in the crystal has been cited as a cause, the concentration of impurities in the crystal can be determined by repeating crystallization. Although a method for reducing the amount has been proposed, this method has a drawback that productivity is poor because crystallization is repeated a plurality of times.

[0004]

The problem to be solved by the present invention
The cause of the crystal defects in the BGO crystal is considered to be the effect of phases other than bismuth germanate (Bi ₄ Ge ₃ O ₁₂ ) in the BGO crystal.
₂ O ₃ and GeO ₂ are mixed at a predetermined ratio (usually stoichiometric ratio) and fired at an appropriate temperature to produce a Bi ₄ Ge ₃ O ₁₂ composition in advance, which is used as a raw material. It has been proposed for use (G. Gevay, Prog. Cryst. Growth and Charact. 15
(1987) 145), which also discloses the firing temperature, firing time, number of firings, and the like.

However, when a baking material is actually prepared by this known method, and a BGO crystal is grown by using the baking material by the Czochralski method or the Bridgman method, and a scintillator is prepared therefrom, There was a defect that the amount of luminescence was smaller than that of a scintillator made of a crystal grown from a raw material prepared by a known method.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a method for producing a BGO crystal which can solve such disadvantages, and comprises a method for producing a mixture of bismuth oxide and germanium oxide from a melt of a fired composition. In growing a bismuth acid single crystal, a raw material prepared under firing conditions with a temperature rising rate of 10 ° C./min or more is used.

[0007] That is, the present inventors consider that B
As a result of various studies to develop a method for manufacturing GO crystals, it was found that if high-purity bismuth oxide (Bi ₂ O ₃ ) and germanium oxide (GeO ₂ ) were mixed and fired, the amount of impurities in the crystal would naturally be If the rate of temperature rise during this firing is set to a rapid rise of 10 ° C./min or more, the undesirable phenomenon of melting or evaporating Bi ₂ O _{3 which} causes a compositional deviation can be prevented. The present inventors have found that the amount of the hetero phase in the raw material can be reduced, and confirmed that the BGO crystal having excellent physical properties can be obtained according to the finding, thereby completing the present invention. This will be described in more detail below.

[0008]

The present invention relates to a method for producing a BGO crystal, which uses a raw material prepared under sintering conditions at a heating rate of 10 ° C./min or more when growing a BGO crystal from a melt. According to this, the amount of impurities is reduced, and the amount of bismuth germanate in a different phase other than BGO is reduced, thereby providing an advantage that a BGO crystal having excellent physical properties can be obtained.

In the method for producing a BGO crystal according to the present invention, when growing a BGO crystal from a melt, the sintering conditions of the raw material composition are specified. This raw material composition is composed of bismuth oxide (Bi ₂ O ₃ ). And germanium oxide (GeO ₂ ) in a stoichiometric ratio. Since the bismuth oxide and the germanium oxide reduce the amount of impurities contained in the raw material for firing, it is necessary that the purity be 99% or more. Is preferred. However, in this mixture of stoichiometric ratio of Bi ₂ O ₃ and GeO ₂ , P. Tissot and H, Lartique, Thermoc
As shown in FIG. 1 described in himica Acta. 127 (1983) 377-383, besides Bi ₃ Ge ₄ O ₁₂ , for example, Bi ₁₂
The inclusion of a composition as shown by GeO ₂₀ ,
Investigation by X-ray diffraction method by the present inventors revealed this.

Then, as in the case of B ₁₂ GeO ₂₀ , Be ₃ Ge ₄ O ₁₂
If other components (hereinafter referred to as “heterophase”) are contained, the heterophase remains in the melt even if it is heated and dissolved in a crucible, so this heterophase is incorporated into the grown crystal. It was presumed that the properties as a scintillator deteriorated.

However, the present inventors have studied a parameter of a heating rate, which was not conventionally known, for the firing conditions of the firing raw material. If the heating rate is set to 10 ° C./minute, a different phase in the firing raw material is obtained. Is found to be reduced, and therefore BGO
It was found that crystals were obtained.

Therefore, in the method for producing a BGO crystal according to the present invention, the heating rate of the raw material for firing is set to 10% / min or more, which is preferably set to 15 minutes or more. When the temperature is lower than 850 ° C, the relative amount of Bi ₁₂ GeO ₂₀ increases due to the low rate of formation into BGO,
If the temperature is higher than ℃, the cause is unknown, but the ratio of the different phases becomes high.

If the firing time is less than 20 hours, the reaction to BGO does not proceed sufficiently. Therefore, it is preferable to set the firing time to 20 hours or more. And the thickness is preferably 7 cm or less since the rate of temperature rise is substantially reduced.

[0014]

Next, examples of the present invention will be described. Example 5,991 g of bismuth oxide (Bi ₂ O ₃ ) having a purity of 99.999% or more and 2,025 g of germanium oxide (GeO ₂ ) having a purity of 99.999% or more
Was weighed and mixed in a ball mill for 5 hours, then charged into an alumina container lined with platinum foil, and fired in a muffle furnace equipped with a thermocouple.

This experiment was carried out by changing 1) the firing temperature, 2) the firing time, and 3) the firing temperature. First, the amount of Bi ₁₂ GeO ₂₀ in the raw material after firing was determined. However, it was decided to use a sample in which BGO crystal and B ₁₂ GeO ₂₀ crystal were mixed at a predetermined ratio, using a powder X-ray diffractometer as an apparatus and CuKα1 as an X-ray source, The X-ray diffraction spectrum was measured with the BGO peak at 2θ = 34.2 ° and the B ₁₂ GeO ₂₀ peak at 2θ = 33 ° to prepare a calibration curve (see FIG. 2).
The peak ratio of Bi ₁₂ GeO ₂₀ was determined.

[0016] From the results as shown in Figure 3 the correlation between the weight% of the peak ratio and Bi ₁₂ GeO ₂₀ of BGO and Bi ₁₂ GeO ₂₀ about this is obtained, Bi ₁₂ Ge by 3
It was confirmed that the weight percentage of O ₂₀ was required, and 850
When baked at 20 ° C for 20 hours, the rate of temperature increase is 2 ° C / min.
When the weight% of B ₁₂ GO ₂₀ as a foreign phase in the calcined product obtained at that time was changed to 14 ° C./min, and the result as shown in FIG. 4 was obtained, It was confirmed that when the heating rate was 10 ° C./min or more, particularly 15 ° C./min or more, the abundance of the foreign phase could be reduced.

Next, the firing temperature is set to 800 to 9
When the weight% of B ₁₂ GeO ₂₀ as a hetero phase in the fired composition when the temperature was changed in the range of 00 ° C. for 1 hour was examined, the result shown in FIG. 5 was obtained. Since it is too high at 900 ° C. and the weight% of the heterophase becomes high, it has been found that the temperature should be 850 to 880 ° C.

The firing time at 850.degree.
When sintering for 40 hours to 40 hours, the results shown in FIG. 6 are obtained. In 5 hours, the weight% of the heterophase does not decrease so much, and in 10 hours, it becomes about 15%. If it is above, it will be 5% or less, so this is more than 10 hours,
Preferably, it is 20 hours or more.

The sintering is carried out after a mixture of bismuth oxide and germanium oxide is uniformly mixed in a ball mill, and is usually formed into a flat plate for uniform sintering. The relationship between the thickness of the plate and the weight% of B ₁₂ GeO ₂₀ as a different phase was examined. The result was as shown in FIG.
Since the weight% of this hetero phase increased, it was found that the thickness should be 7 cm or less.

[0020]

The present invention relates to a method for producing a BGO crystal, which, when growing a BGO crystal from a melt of a mixed sintering composition of bismuth oxide and germanium oxide, as described above, increases the temperature rise rate. It is characterized by using a raw material prepared under sintering conditions of 10 ° C./min or more. According to this, the content of impurities is small, and the content of a heterophase bismuth germanate single crystal such as Bi ₁₂ GeO ₂₀ is contained. Since a mixed sintering composition of bismuth oxide and germanium oxide with a small amount can be obtained, it is considered to be excellent in physical properties, and thus useful for optics and scintillators.
The advantage is that BGO crystals can be obtained easily.

[Brief description of the drawings]

FIG. 1 shows a composition diagram of a mixture of Bi ₂ O ₃ and GeO ₂ by an X-ray diffraction method.

FIG. 2 shows an X-ray diffraction spectrum of a fired composition of Bi ₂ O ₃ and GeO ₂ .

FIG. 3 Peak ratio between BGO and Bi ₁₂ GeO ₂₀ and Bi ₁₂ GeO ₂₀
FIG. 2 is a diagram showing a correlation with the weight% of the sample.

FIG. 4 is a diagram showing a correlation between a heating rate of a fired composition of Bi ₂ O ₃ and GeO ₂ and a weight% of Bi ₁₂ GeO ₂₀ as a different phase.

FIG. 5 is a diagram showing a correlation between the sintering temperature and the weight% of Bi ₁₂ GeO ₂₀ as a different phase in a sintering composition of Bi ₂ O ₃ and GeO ₂ .

FIG. 6 is a diagram showing a correlation between the sintering time in the sintering composition of Bi ₂ O ₃ and GeO ₂ and the weight% of Bi ₁₂ GeO ₂₀ as a different phase.

FIG. 7 is a graph showing a correlation between the thickness of a baked composition plate of Bi ₂ O ₃ and GeO ₂ and the weight% of Bi ₁₂ GeO ₂₀ as a different phase.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Toshihiko Nagao 2-13-1 Isobe, Annaka-shi, Gunma Prefecture Shin-Etsu Chemical Co., Ltd. Precision Functional Materials Laboratory (56) References JP-A-2-74596 ( JP, A) JP-A-1-320295 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C30B 29/32

Claims (2)

(57) [Claims] In growing a bismuth germanate single crystal from a melt of a mixed firing composition of bismuth oxide and germanium oxide, a raw material adjusted under firing conditions of a temperature rising rate of 10 ° C./min or more is used. A method for producing a bismuth germanate single crystal, comprising: 2. The sintering temperature is in the range of 850 ° C. to 880 ° C.,
2. The sintering time is 20 hours or more.
The method for producing a single crystal of bismuth germanate described in 1 above.