JP2003267799A - Magnesium lithium niobate single crystal and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnesium lithium niobate single crystal which has only small optical damage, no segregation of Mg in the crystal and a uniform crystal composition, and to provide a method for producing the same. <P>SOLUTION: The magnesium lithium niobate single crystal has an atomic ratio of Li to Nb of 0.9425≤Li/Nb≤0.9440 and a Mg content of from more than 5.00 mol% to 5.30 mol%. The method for producing the magnesium lithium niobate single crystal comprises a raw material mixture preparation step for preparing a raw material mixture by mixing Li<SB>2</SB>CO<SB>3</SB>, Nb<SB>2</SB>O<SB>5</SB>and MgO in an atomic ratio of Li to Nb of 0.9425≤Li/Nb≤0.9440 and in a molar ratio of LiNbO<SB>3</SB>to MgO of 0.050<MgO/(MgO+LiNbO<SB>3</SB>)≤0.053; a raw material mixture melting step; and a single crystal growing step. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium niobate single crystal used for optical elements such as optical modulators and wavelength conversion elements.

[0002]

2. Description of the Related Art A single crystal of lithium niobate is widely used as an optical element such as an optical modulator or a wavelength conversion element.
However, when a substrate of a lithium niobate single crystal is irradiated with laser light of a short wavelength of green or blue, so-called optical damage occurs in which the refractive index changes due to the photoinduced refractive index effect. Due to this optical damage, the beam that has passed through the lithium niobate single crystal spreads, and the intensity of the laser light decreases. Therefore, suppressing this optical damage is very important for practical application of the lithium niobate single crystal.

Various studies have been conducted in order to suppress optical damage in lithium niobate single crystals. For example, addition of some elements as dopants into a lithium niobate single crystal has been studied. One of them is a lithium niobate single crystal with congruent composition,
It has been reported that photodamage can be suppressed by adding magnesium (Mg) in an amount of 4.5 mol% or more (DABryan,
R. Gerson, HE Tomaschke, Appl. Phys. Lett, 44 (1984) 847
~ 849). Here, the congruent composition is a composition in which the melt composition and the single crystal composition obtained from the melt match, that is, a so-called matching melt composition.

[0004]

However, in the single crystal obtained by adding about 4.5 mol% of Mg to the lithium niobate single crystal having the above congruent composition, the optical damage is suppressed to some extent, but its optical damage resistance property is not sufficient. It wasn't very good. Further, there is a problem that the crystal is likely to be cracked and that segregation of Mg is present to make the composition non-uniform between the upper part and the lower part of the crystal. If the composition in the crystal is not uniform, the refractive index changes, and the homogeneity for optical use cannot be maintained. In addition, since the intensity of the laser beam that passes through is reduced, it is practically difficult to use.

The present invention has been made in order to solve the above problems, and provides a lithium magnesium niobate single crystal having a small optical damage, no segregation of Mg in the crystal, and a uniform crystal composition. This is an issue. Another object is to provide a method for easily producing such a lithium magnesium niobate single crystal.

[0006]

The lithium magnesium niobate single crystal of the present invention has a Li to Nb atomic ratio of 0.
9425 ≦ Li / Nb ≦ 0.9440, and the content ratio of Mg is more than 5.00 mol% and not more than 5.30 mol%.

By adjusting the atomic ratio of Li and Nb in the crystal and the amount of Mg in the crystal, the present inventor not only causes less optical damage but also prevents the segregation of Mg, which is a lithium magnesium niobate single crystal. I thought that I could get.

Generally, a lithium niobate single crystal having a congruent composition has a defect structure having a defect at a lithium site. Then, Mg is added to the lithium niobate single crystal.
Is added, Mg atoms are first arranged in the defects,
It is considered that the excess Mg is arranged in niobium site.
The present inventor has found that if the added Mg has almost the same number as the number of defects in the crystal structure of the lithium niobate single crystal, it is unlikely to cause optical damage, and that the segregation of Mg is small and the composition of the single crystal is uniform. I got the knowledge that. That is, when the amount of Mg is larger than the number of defects, the excessive Mg makes the crystal structure unstable and segregates Mg easily. On the contrary, even if Mg is less than the number of defects, the composition in the crystal becomes non-uniform.

The lithium magnesium niobate single crystal of the present invention is based on the above findings. Focusing on defects in the crystal structure of the lithium niobate single crystal, Li and Nb
By adjusting the atomic ratio with and the amount of Mg in the crystal to be appropriate, a single crystal with less photodamage and a uniform composition without segregation of Mg in the crystal can be obtained.

The method for producing the lithium magnesium niobate single crystal of the present invention is not particularly limited. For example, it can be easily produced by the following method of the present invention. That is, in the method for producing a lithium magnesium niobate single crystal of the present invention, lithium carbonate (Li ₂ CO ₃ ) serving as a lithium source, niobium pentoxide (Nb ₂ O ₅ ) serving as a niobium source, and magnesium oxide serving as a magnesium source ( MgO) and the following two conditions: (1) Li and Nb
Atomic ratio with 0.9425 ≦ Li / Nb ≦ 0.944
0 (2) Molar ratio of LiNbO ₃ and MgO when LiNbO ₃ is generated from Li ₂ CO ₃ and Nb ₂ O ₅ ; 0.050 <MgO / (MgO + LiNbO
₃ ) A raw material mixture preparation step of preparing a raw material mixture by mixing so as to satisfy ≦ 0.053, a raw material mixture melting step of melting the raw material mixture to obtain a raw material mixture melt, and a raw material mixture melt A single crystal growing step of growing a lithium magnesium niobate single crystal by immersing the seed crystal in and pulling it.

Conventionally, when a predetermined raw material containing Mg is mixed and melted to grow a crystal by, for example, the Czochralski method, in the grown crystal and the residual melt,
There is a problem that the distribution coefficient of Mg does not become 1.
That is, in the melt as the raw material and the grown crystal, M
The content ratio of g is different. For this reason, a concentration gradient of Mg was generated in the process of pulling up the crystal, and the composition of the grown crystal was non-uniform between the first pulled up portion and the later pulled up portion, that is, the upper and lower portions of the crystal. .

In the production method of the present invention, attention is paid to the composition of a three-component raw material composed of a lithium source, a niobium source and a magnesium source, and the mixing ratio of each raw material is determined by the distribution coefficient of Mg between the crystal and the residual melt. It is specified so that it becomes almost 1. That is, by using as a starting material a raw material mixture in which the above three kinds of compounds as raw materials are mixed so as to satisfy the conditions (1) and (2), the distribution coefficient of Mg between the crystal and the residual melt is obtained. Can be approximately 1. When the distribution coefficient of Mg becomes approximately 1, the composition becomes uniform in the upper part and the lower part of the crystal, and it becomes difficult for Mg to segregate. Therefore, according to the production method of the present invention, a homogeneous lithium magnesium niobate single crystal with little optical damage can be easily obtained by simply mixing the three kinds of compounds as raw materials in the above-mentioned specific ratios.

Further, the lithium magnesium niobate single crystal obtained by the production method of the present invention has a small amount of segregation of Mg and a uniform composition, so that the occurrence of cracks is small.
The light-damage resistance is good in the entire crystal. Therefore, according to the production method of the present invention, it is possible to obtain a high yield of a lithium magnesium niobate single crystal with less light damage and a uniform crystal composition.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The lithium magnesium niobate single crystal of the present invention and the method for producing the same will be described in detail below. The embodiment to be described is only one embodiment, and the lithium magnesium niobate single crystal of the present invention and the manufacturing method thereof are not limited to the following embodiments. The present invention can be implemented in various forms including modifications and improvements that can be made by those skilled in the art, including the following embodiment.

<Lithium magnesium niobate single crystal>
The lithium magnesium niobate single crystal of the present invention is made of Li
And Nb atomic ratio 0.9425 ≦ Li / Nb ≦ 0.9
It is 440, and the content ratio of Mg is more than 5.00 mol% and not more than 5.30 mol%.

The atomic ratio of Li and Nb is 0.942 in consideration of the congruent composition of the lithium niobate single crystal.
5 ≦ Li / Nb ≦ 0.9440. When the value of Li / Nb is less than 0.9425, the fluctuation of the crystal composition becomes large, that is, since the atomic ratio of Li and Nb is different between the upper part and the lower part of the crystal, it becomes a light scattering factor. This is because the light damage resistance is deteriorated. Especially, 0.9429 ≦ L
It is more preferable to use i / Nb. Also, when the value of Li / Nb exceeds 0.9440, the fluctuation of the crystal composition becomes large, and the light damage resistance property becomes low as in the above. In particular, Li / Nb ≦ 0.9436 is more preferable.

The Mg content is more than 5.00 mol% and not more than 5.30 mol%. Here, the content ratio of Mg means the content ratio of Mg when the total atoms constituting the lithium magnesium niobate single crystal of the present invention is 100 mol%. Mg content 5.00 mol%
In the following cases, the crystal composition becomes non-uniform and the light damage resistance property becomes poor. Particularly, it is more preferable to set it to 5.05 mol% or more. On the other hand, when the content ratio of Mg exceeds 5.30 mol%, segregation of Mg occurs in the crystal and the composition becomes non-uniform, resulting in low light damage resistance. Particularly, it is more preferable to set it to 5.20 mol% or less.

<Manufacturing Method of Lithium Magnesium Niobate Single Crystal> The manufacturing method of the lithium magnesium niobate single crystal of the present invention comprises a raw material mixture preparing step, a raw material mixture melting step, and a single crystal growing step. It Hereinafter, each step will be described.

(1) Raw Material Mixture Preparation Step In this step, lithium carbonate (Li ₂ C) which becomes a lithium source is used.
O ₃ ), niobium pentoxide (Nb ₂ O ₅ ) serving as a niobium source, and magnesium oxide (MgO) serving as a magnesium source,
The following two conditions, (1) atomic ratio of Li and Nb;
9425 ≦ Li / Nb ≦ 0.9440 (2) Molar ratio of LiNbO ₃ and MgO when LiNbO ₃ is generated from Li ₂ CO ₃ and Nb ₂ O ₅ ; 0.050 <MgO / (MgO + LiNbO
₃ ) A step of preparing a raw material mixture by mixing so as to satisfy ≦ 0.053.

Li ₂ CO _{3 serving as a} lithium source and Nb ₂ O _{5 serving as a} niobium source have an atomic ratio of Li to Nb of 0.942.
Mix so that 5 ≦ Li / Nb ≦ 0.9440.
When the value of Li / Nb is less than 0.9425, the distribution coefficient of Mg in the grown crystal and the residual melt does not become 1, and the composition becomes uneven in the upper and lower parts of the obtained crystal. Become. Therefore, the content ratio of Mg varies in the crystal, which becomes a light scattering factor and deteriorates the light damage resistance. In particular, 0.9429 ≦ Li / Nb is more preferable. Further, when the value of Li / Nb exceeds 0.9440, similarly, the distribution coefficient of Mg does not become 1, and in addition, segregation of Mg occurs in the crystal and the composition becomes nonuniform, so that the light damage resistance characteristic is improved. Get lower. In particular, Li / Nb ≦ 0.
9436 is more preferable.

Further, the chemical formula of a single crystal of lithium niobate produced from Li ₂ CO ₃ and Nb ₂ O ₅ is LiNbO.
_{As 3} , the mixing ratio of MgO is determined. This allows
The content ratio of Mg in the generated lithium magnesium niobate single crystal is determined. Specifically, MgO serving as a magnesium source has a molar ratio of LiNbO ₃ and MgO of 0.050 <MgO / (MgO + LiNbO).
₃ ) Mix so that ≦ 0.053. MgO / (M
When gO + LiNbO ₃ ) ≦ 0.050, the distribution coefficient of Mg in the grown crystal and the residual melt does not become 1, and the composition becomes non-uniform in the upper and lower parts of the obtained crystal. This is because the light damage resistance property is deteriorated. In particular,
It is more preferable to set 0.0505 ≦ MgO / (MgO + LiNbO ₃ ). In addition, 0.053 <MgO / (M
In the case of gO + LiNbO ₃ ), similarly, the distribution coefficient of Mg does not become 1, and the segregation of Mg occurs in the crystal to make the composition non-uniform, resulting in low light damage resistance. In particular, MgO / (MgO + LiNbO ₃ ) ≦ 0.
A value of 052 is more suitable. When MgO is mixed in the above range, the content ratio of Mg in the obtained crystal is 5.05 mol% or more and 5.20 mol% or less. The three kinds of raw materials may be mixed by a known method, for example, using a ball mill or the like. The mixing time is not particularly limited, and may be about 10 hours, for example.

Alternatively, the above raw materials may be mixed to prepare a raw material mixture, which is then calcined for use in the next step. In this case, the production method of the present invention is configured to further include a raw material mixture firing step of firing the prepared raw material mixture after the raw material mixture preparation step. The firing temperature in the raw material mixture firing step is not particularly limited and may be, for example, in the range of 900 to 1200 ° C. Further, the firing may be performed once or may be performed in plural times. The firing time is not particularly limited and may be about 10 hours.

(2) Raw Material Mixing Step This step is a step of melting the raw material mixture obtained in the previous step to obtain a raw material mixture melt. The method of melting the raw material mixture is not particularly limited. For example, the raw material mixture may be put into a platinum crucible and melted by high frequency induction heating. The melting temperature is 1260 to 1300 ° C.
And it is sufficient.

(3) Single crystal growing step This step is a step of growing a lithium magnesium niobate single crystal by immersing a seed crystal in the raw material mixture melt obtained in the raw material mixture melting step and pulling it up. . Here, as the seed crystal, a lithium niobate single crystal piece cut out in the intended axis direction may be used. This seed crystal is dipped in the raw material mixture melt and pulled up to grow a lithium magnesium niobate single crystal. The conditions for pulling the single crystal are not particularly limited, and for example, the number of rotations is 5 to 20 rpm, the pulling rate is 1 to 10 mm / hr.
And so on.

[0025]

EXAMPLES Various lithium magnesium niobate single crystals of the present invention were produced based on the above-described embodiments. Also,
As a comparative example, a lithium magnesium niobate single crystal was manufactured by changing the composition of the raw material mixture. Then, various measurements were performed on the manufactured lithium magnesium niobate single crystal to evaluate the light damage resistance property. Hereinafter, the production of lithium magnesium niobate single crystal, the respective measurement results, and the evaluation of the light damage resistance property will be described.

<Production of Lithium Magnesium Niobate Single Crystal> (1) 5 lithium magnesium niobate single crystals having a Li / Nb value of 0.9433 and a Mg content of 5.00 to 5.40 mol%. Type manufactured.

First, the Li / Nb value is set to 0.9433, and the molar ratio of LiNbO ₃ and MgO, that is, the value of MgO / (MgO + LiNbO ₃ ) is 0.0.
Li ₂ CO ₃ and N so that each value is 50 to 0.054.
b ₂ O ₅ and MgO were mixed by a ball mill to prepare five kinds of raw material mixtures. 10 of the prepared raw material mixture
After firing at 00 ° C. for 10 hours, it was put into a platinum crucible and melted by high frequency induction heating. Melting temperature is 1300 ℃
And A seed crystal was immersed in this raw material mixture melt and pulled up at a rotation speed of 10 rpm and a pulling rate of 5 mm / hr to obtain a single crystal having a diameter of about 80 mm and a length of about 60 mm.
The obtained lithium magnesium niobate single crystal was # 11.
˜ # 15 single crystals.

(2) The value of Li / Nb is 0.9421 to 0.9421.
Four kinds of lithium magnesium niobate single crystals having 0.9444 and a Mg content of 5.15 mol% were manufactured.

First, the value of Li / Nb is 0.9421-
0.944 and the molar ratio of LiNbO ₃ and MgO, that is, MgO / (MgO + Li
NbO ₃ ) value of 0.0515, so that Li ₂ CO
_Three kinds of raw material mixtures were prepared by mixing ₃ with Nb ₂ O ₅ and MgO. Hereinafter, # 11 to # 1 in the above (1)
Each single crystal was obtained by manufacturing in the same manner as the single crystal of No. 5. The obtained lithium magnesium niobate single crystals were # 21 to # 24.
Are numbered as single crystals.

<Evaluation of optical damage resistance of manufactured lithium magnesium niobate single crystal> The manufactured # 11 to #
For each lithium magnesium niobate single crystal of No. 15, # 21 to # 24, 5 mm from the upper end of the crystal, 3
A 1 mm thick crystal block was cut out from the 0 mm and 60 mm portions. In the crystal, the side closer to the seed crystal, that is, the end that was pulled up earlier was set as the upper end. Then, both sides of the block were mirror-polished to prepare a measurement wafer. That is, for each lithium magnesium niobate single crystal, three types of measurement wafers, that is, an upper part, a middle part, and a lower part, were prepared by cutting out. Various measurements and analyzes were performed using the manufactured measurement wafers. The following is a description of each item.

(1) Calculation of distribution coefficient of Mg In order to obtain a distribution coefficient of Mg between the obtained lithium magnesium niobate single crystal and the residual melt, the Mg content ratio of each of the above-mentioned wafers and residual melts prepared was determined. It analyzed by the inductively coupled plasma optical emission spectrometry (ICP-AES). Then, for each lithium magnesium niobate single crystal,
The average value of the content ratios of Mg in the three wafers was calculated. The distribution coefficient of Mg was obtained by dividing the average value by the value of the content ratio of Mg in each residual melt.

(2) Measurement of Refractive Index Fluctuation Depending on Crystal Position The refractive index of each wafer prepared above was analyzed by a prism coupler (PC-2000 manufactured by METRICON). The measurement conditions are a wavelength of 632.8 nm and a temperature of 24 ° C.
And Then, for each lithium magnesium niobate single crystal, the difference between the refractive index of the wafer cut out from the upper part and the refractive index of the wafer cut out from the lower part was obtained, and the difference value was taken as the refractive index variation value.

(3) Observation of transmitted beam shape In order to examine whether or not there is a change in the refractive index when irradiated with laser light, that is, whether or not there is optical damage, each of the above manufactured wafers is irradiated with high-power argon green laser light. The shape of the transmitted beam was observed. When the laser light irradiation causes optical damage that changes the refractive index, the shape of the transmitted beam changes. FIG. 1 schematically shows the optical system used for observation.
The optical system 1 includes an argon laser 10, a mirror 20, a lens 30, a measurement wafer 40, and a screen 50. Power controller 11 for argon laser 10
Is attached. The filter 12 is arranged between the mirror 20 and the lens 30. The wavelength of the argon laser 10 is adjusted to 488 nm, and the power density is 1.7M by the power controller 11 and the filter 12.
It is adjusted to W / cm ² .

The laser light emitted from the argon laser 10 is narrowed down by the lens 30 via the mirror 20.
The beam shape before being incident on the measurement wafer 40 is circular, and the radius thereof is 20 μm. Then, the beam incident on the measurement wafer 40 and transmitted through the measurement wafer 40 is projected on the screen 50. Each of the above wafers was used as the measurement wafer 40, and the shape of the beam transmitted through each wafer was observed.

(4) Crack-free rate At the time of production of lithium magnesium niobate single crystals having the above-mentioned compositions, it was investigated at what rate cracks were generated. 20 lithium magnesium niobate single crystals each having the above composition were produced by the above method, and the ratio of those in which no cracks were generated was calculated to be the crack free rate (%).

(5) Yield Regarding each of the lithium magnesium niobate single crystals of # 11 to # 15 and # 21 to # 24 produced above, the entire portion where the refractive index did not change even when irradiated with laser light I calculated the ratio. Specifically, each manufactured lithium magnesium niobate single crystal was cut into crystal blocks having a thickness of 1 mm, and both surfaces of each crystal block were mirror-polished to obtain a wafer. Each wafer was irradiated with laser light to measure the change in refractive index. Then, the value obtained by the following equation [(number of wafers whose refractive index did not change / total number of wafers) × 100] was defined as the yield (%).

(6) Measurement Results and Evaluation of Light Damage Resistance Characteristics Tables 1 and 2 collectively show the analysis and measurement results of the above (1) to (5). Table 1 shows the results for each of the lithium magnesium niobate single crystals # 11 to # 15.
Table 2 shows the results for each of the lithium magnesium niobate single crystals # 21 to # 24. In Tables 1 and 2, the presence / absence of segregation of Mg is determined based on the visual observation and the change in the shape of the transmitted beam. Further, regarding the change of the shape of the transmitted beam, when the major axis of the shape of the transmitted beam is about doubled and the shape of the transmitted beam is changed to an elliptical shape, scattering is defined.

[0038]

[Table 1]

[0039]

[Table 2]

First, Table 1 will be described. From Table 1,
# 1 with a Mg content of 5.05 to 5.30 mol%
The lithium magnesium niobate single crystals of # 2, # 13, and # 14 all had a distribution coefficient of Mg of about 1. This indicates that the single crystal and the residual melt have almost the same Mg content. That is, the composition is uniform between the upper part and the lower part of the crystal. This can also be confirmed from the fact that the refractive index fluctuation value is small. On the other hand, the Mg content is 5.00 mol% or 5.40 mol% #
The lithium magnesium niobate single crystals of No. 11 and # 15 have Mg distribution coefficients of 0.993 and 1.004, respectively.
Became. Therefore, the content ratio of Mg was different between the upper part and the lower part of the crystal, and the refractive index fluctuation value was also large.

The # 12, # 13, and # 14 lithium magnesium niobate single crystals showed no change in the shape of the transmitted beam even when the above-mentioned laser light was irradiated to each wafer produced from them. I couldn't do it. That is, it can be seen that even when the laser beam was irradiated with a high power density of 1.7 MW / cm ² , the refractive index did not change and no optical damage occurred. It was confirmed visually that segregation of Mg did not occur. This is presumably because Mg entered the lithium site defects in the crystal so as to be saturated and the crystal structure was stabilized. On the other hand, in the lithium magnesium niobate single crystals of # 11 and # 15, the shape of the beam transmitted through each wafer was changed. Specifically, the shape of the beam transmitted through the wafer manufactured from the bottom of each single crystal changed from a circular shape to an elliptical shape. This indicates that the irradiation of laser light changed the refractive index and caused optical damage. In addition, # 15
Segregation of Mg was observed in the wafer manufactured from the lower part of the lithium magnesium niobate single crystal in Example 1.

Further, the lithium magnesium niobate single crystals of # 12, # 13 and # 14 hardly generate cracks, and there is almost no portion where the refractive index changes even when irradiated with laser light, and the yield is high. You can confirm that. On the other hand, it can be seen that in the # 11 lithium magnesium niobate single crystal, cracks are likely to occur and the yield is low.
Similarly, with the # 15 lithium magnesium niobate single crystal, the yield of cracks was found to be low, although the crack occurrence rate was slightly reduced.

From the above, the value of Li / Nb is 0.943.
3, and 0.050 <MgO / (MgO + LiNbO
₃ ) The lithium magnesium niobate single crystal of the present invention produced by mixing the respective raw materials so as to satisfy the following condition:
It was confirmed that the composition was uniform in the upper part and the lower part of the crystal, and the single crystal was excellent in light damage resistance.

Next, Table 2 will be described. From Table 2,
The values of Li / Nb are 0.9425 and 0.9440 #
In each of the lithium magnesium niobate single crystals of No. 22 and # 23, the distribution coefficient of Mg was almost 1. This indicates that the single crystal and the residual melt have almost the same Mg content. That is, the composition is uniform between the upper part and the lower part of the crystal. This can also be confirmed from the fact that the refractive index fluctuation value is small. On the other hand, in the lithium magnesium niobate single crystals # 21 and # 24 having Li / Nb values of 0.9421 and 0.9443, the distribution coefficients of Mg were 0.997 and 1.003, respectively. . Therefore, the content ratio of Mg differs between the upper part and the lower part of the crystal,
The refractive index fluctuation value also became large.

Further, the # 22 and # 23 lithium magnesium niobate single crystals showed no change in the shape of the transmitted beam even when each of the wafers produced from them was irradiated with the above laser beam. . In other words, 1.7M
It can be seen that even when laser light was irradiated at a high power density of W / cm ² , the refractive index did not change and optical damage did not occur. It was confirmed visually that segregation of Mg did not occur. On the other hand, in the lithium magnesium niobate single crystals of # 21 and # 24, the shape of the beam transmitted through each wafer was changed. Specifically, the shape of the beam transmitted through the wafer manufactured from the bottom of each single crystal changed from a circular shape to an elliptical shape. This indicates that the irradiation of laser light changed the refractive index and caused optical damage. Further, in the wafer manufactured from the lower part of the # 24 lithium magnesium niobate single crystal, Mg segregation occurred.

Further, it was confirmed that the lithium magnesium niobate single crystals of # 22 and # 23 had almost no cracks and that the refractive index was hardly changed even when the laser beam was irradiated, and the yield was high. it can. on the other hand,#
It can be seen that the 21 and # 24 lithium magnesium niobate single crystals relatively easily cause cracks and the yield is low.

From the above, the value of Li / Nb is 0.9425.
≦ Li / Nb ≦ 0.9440, and MgO / (MgO
The lithium magnesium niobate single crystal of the present invention produced by mixing the respective raw materials so that the value of + LiNbO ₃ ) is 0.0515 has a uniform composition in the upper and lower parts of the crystal, and has excellent light damage resistance characteristics. It was confirmed that it became an excellent single crystal.

In summary, the value of Li / Nb is 0.942.
The lithium magnesium niobate single crystal of the present invention in which 5 ≦ Li / Nb ≦ 0.9440 and the content ratio of Mg is more than 5.00 mol% and 5.30 mol% is composed of the upper part and the lower part of the crystal. It was confirmed that the single crystal was uniform and had no segregation of Mg and was excellent in light damage resistance. By using such a lithium magnesium niobate single crystal of the present invention, a high-performance optical element can be realized in the fields of wavelength conversion elements such as SHG, optical modulators, optical switches, and high-power lasers.

[0049]

The lithium magnesium niobate single crystal of the present invention has an atomic ratio of Li to Nb of 0.9425 ≦ Li.
/Nb≦0.9440 and the content ratio of Mg is 5.0
Since it is more than 0 mol% and not more than 5.30 mol%, a single crystal having a uniform composition with less optical damage and no segregation of Mg in the crystal is obtained. Further, according to the production method of the present invention, the partition coefficient of Mg between the produced crystal and the residual melt can be made approximately 1. Therefore, the composition becomes uniform in the upper part and the lower part of the crystal, and it becomes difficult for Mg to segregate. Therefore, according to the production method of the present invention, the lithium magnesium niobate single crystal of the present invention can be easily produced in high yield.

[Brief description of drawings]

FIG. 1 schematically shows an optical system used for observation of a transmitted beam shape.

[Explanation of symbols]

1: Optical system 10: Argon laser 11: Power controller
12: filter 20: mirror 30: lens 40: wafer for measurement
50: Screen

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Masato Kurachi             971 Anada-cho, Seto-shi, Aichi Yamajuse Co., Ltd.             In Ramix F-term (reference) 2H079 AA02 AA12 BA01 DA03 JA00                 2K002 AB12 BA03 CA03 FA03 GA10                       HA20                 4G077 AA02 BC32 CF10 EA02 EC08                       HA01

Claims (4)

[Claims] 1. The atomic ratio of Li and Nb is 0.9425 ≦
Li / Nb ≦ 0.9440, and a magnesium magnesium niobate single crystal in which the content ratio of Mg is more than 5.00 mol% and not more than 5.30 mol%. 2. The atomic ratio of Li to Nb is 0.942.
The lithium magnesium niobate single crystal according to claim 1, wherein 9 ≦ Li / Nb ≦ 0.9436. 3. The lithium magnesium niobate single crystal according to claim 1, wherein the content ratio of Mg is 5.05 mol% or more and 5.20 mol% or less. 4. Lithium carbonate (Li ₂
CO ₃ ), niobium pentoxide (Nb ₂ O ₅ ) serving as a niobium source, and magnesium oxide (MgO) serving as a magnesium source, the following two conditions: (1) atomic ratio of Li and Nb; 0.9425 ≤ Li /
Nb ≦ 0.9440 (2) Molar ratio of LiNbO ₃ and MgO when it is assumed that LiNbO ₃ is produced from Li ₂ CO ₃ and Nb ₂ O ₅ ; 0.050 <MgO / (MgO + LiNbO
₃ ) A raw material mixture preparing step of preparing a raw material mixture by mixing so as to satisfy ≦ 0.053, a raw material mixture melting step of melting the raw material mixture to obtain a raw material mixture melt, and a raw material mixture melt A method for producing a lithium magnesium niobate single crystal, which comprises a single crystal growing step of growing a lithium magnesium niobate single crystal by immersing a seed crystal in the above and pulling it up.