JP2021155246A - Lithium niobate single crystal and method for manufacturing the same - Google Patents

Abstract

To provide a high quality lithium niobate single crystal excellent in the uniformity of curie temperature, and a manufacturing method capable of stably providing the single crystal.SOLUTION: The curie temperature of the bottom part of a lithium niobate single crystal is more than 1137°C and less than 1140°C. A method for growing the lithium niobate single crystal includes a step of growing a single crystal using a raw material obtained by mixing a predetermined amount of a Li2CO3 powder and Nb2O5 so that the curie temperature of the grown single crystal is 1137.5°C or more and 1139.5°C or less using 1138.5°C as a center value.SELECTED DRAWING: Figure 3

Description

The present invention relates to a lithium niobate single crystal and a method for producing the same.

Lithium niobate (LiNbO ₃ , hereinafter sometimes abbreviated as "LN") single crystal is an artificial ferroelectric crystal having a melting point of about 1250 ° C. and a Curie temperature of about 1140 ° C. The LN single crystal substrate cut out from the LN single crystal and obtained by polishing is mainly used as a material for a surface acoustic wave element (SAW device) mounted on a mobile communication device.

The LN single crystal is industrially grown mainly by the Czochralski method (hereinafter, may be abbreviated as "Cz"), and for example, the high-frequency dielectric heating type growing furnace described in Patent Document 1 is used. NS. Then, it is usually grown in a platinum crucible in an air atmosphere or in a nitrogen-oxygen mixed gas atmosphere having an oxygen concentration of about 20%. The grown LN single crystal is colorless and transparent or has a highly transparent pale yellow color. The grown LN single crystal undergoes "annealing treatment" to remove residual strain due to thermal stress during growth and cooling, and "polling treatment" to align the electrical polarity of the entire crystal to make it a single polarization. After that, it is handed over to the substrate processing process.

Here, the Cz method is a method of obtaining a single crystal having the same crystal orientation as the seed crystal by bringing the seed crystal into contact with the surface of the raw material melt in the crucible and continuously pulling the seed crystal while rotating it. .. After growing the crystal to the desired size (crystal diameter x crystal length), the grown crystal is separated from the raw material melt by adjusting the crystal pulling speed and melt temperature, and cooled to near room temperature from the growing furnace. Take out the crystals. In crystal growth by the Cz method, it is important to efficiently conduct the latent heat generated by the solidification of the raw material melt at the crystal growth interface upward through the seed crystal, so that it is directed upward from the surface of the raw material melt. It is carried out under a temperature gradient adjusted to reduce the temperature. In the Cz method, a seed crystal having a diameter of about 10 mm or less is generally used, and a single crystal having a diameter several times to several tens of times the diameter of the seed crystal can be grown.

Japanese Unexamined Patent Publication No. 2019-6612

By the way, in growing an LN single crystal, it is important to grow a single crystal having a uniform composition. Since the crystal composition is proportional to the velocity of the elastic wave propagating in the crystal, it has a great influence on the characteristics of the SAW device manufactured by using the LN single crystal substrate. Therefore, the uniformity of the composition needs to be uniform not only within one crystal but also between crystals.

However, since Li, which is a light element, is a constituent element of LN crystals, the composition of LN crystals cannot be accurately measured by chemical analysis or the like. Therefore, the Curie temperature (the temperature at which the LN crystal undergoes a phase transition from a ferroelectric substance to a ferroelectric substance), which is proportional to the composition, is used as a substitute, and the uniformity of the Curie temperature guarantees the uniformity of the composition. LN crystals that have not been grown with an appropriate composition have a problem that the Curie temperature fluctuates within and between crystals.

The present invention focuses on such a problem, and an object of the present invention is to stably provide an LN single crystal having excellent Curie temperature uniformity.

In order to achieve the above object, the lithium niobate single crystal according to one aspect of the present invention is a lithium niobate single crystal.
The Curie temperature of the bottom portion exceeds 1137 ° C and is less than 1140 ° C.

Further, in the method for growing a lithium niobate single crystal according to another aspect of the present invention,
Using a raw material in which a predetermined amount _{of Li 2} CO ₃ powder and Nb ₂ O ₅ are mixed so that the Curie temperature of the single crystal to be grown is 1137.5 ° C or higher and 1139.5 ° C or lower with the Curie temperature of 1138.5 ° C as the center value. It is characterized by having a step of growing a single crystal.

According to the present invention, it is possible to stably provide a high-quality lithium niobate single crystal having excellent uniformity of crystal composition (Curie temperature).

It is sectional drawing which shows typically the schematic structure of the high frequency induction heating type single crystal growth apparatus 130. This is a survey result showing the relationship between the raw material composition and the Curie temperature of the crystal to be grown. It is a figure which showed the change of the Curie temperature when a single crystal was grown a plurality of times by setting a raw material composition according to the target Curie temperature of a single crystal after growing.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

[Overview of single crystal growth device and single crystal growth method]
First, with reference to FIG. 1, a configuration example of the Cz method single crystal growth apparatus 130 generally used in LN single crystal growth and an outline of the single crystal growth method will be described.

FIG. 1 is a cross-sectional view schematically showing a schematic configuration of a high-frequency induction heating type single crystal growing apparatus 130. In the growth of LN single crystals, a resistance heating type single crystal growth device is also used, but in FIG. 1, a high frequency induction heating type single crystal growth device is shown as an example. The differences between the high-frequency induction heating type single crystal growth device and the resistance heating type single crystal growth device are as follows. In the case of a high-frequency induction heating type single crystal growing device, an eddy current is generated on the side wall of the metal crucible 10 installed in the work coil 70 by the high-frequency magnetic field formed by the work coil 70, and the eddy current causes the crucible. The 10 itself becomes a heating element, and forms a temperature environment necessary for melting the raw material 150 in the crucible 10 and growing crystals. In the case of the resistance heating type single crystal growing device, the heat generated by the resistance heating heater installed on the outer periphery of the crucible 10 melts the raw material 150 and forms the temperature environment necessary for crystal growing. Since the essence of the Cz method does not change regardless of which heating method is used, the single crystal growing method using the high-frequency induction heating type single crystal growing device will be described below.

As shown in FIG. 1, the high-frequency induction heating type single crystal growing device 130 arranges the crucible 10 in the chamber 100. The crucible 10 is placed on the crucible stand 20. In the chamber 100, a heat insulating material 50 is arranged so as to surround the crucible 10. Further, the work coil 70 is arranged outside the refractory material 60 so as to surround the crucible 10, and an eddy current flows through the crucible wall by the high frequency magnetic field formed by the work coil 70, and the crucible 10 itself becomes a heating element. A pull-up shaft (seed rod) 80 is provided above the chamber 100 so as to be rotatable and vertically movable by a motor 82. A seed holder 81 for holding the seed crystal 140 is attached to the tip of the lower end of the pulling shaft (seed rod) 80.

Further, if necessary, a reflector 30 extending inward from the upper end of the crucible 10 to cover the peripheral portion of the upper end of the crucible 10 and an afterheater 40 extending upward from the reflector 30 in a cylindrical shape may be provided. Both the reflector 30 and the afterheater 40 function as a heating element in the same manner as the crucible 10, and an eddy current is generated by the work coil 70 to induce heating. The reflector 30 is used to keep the heat inside the crucible 10, and the afterheater 40 is used to keep the raised single crystal warm. Therefore, the reflector 30 and the afterheater 40 are made of a metal material capable of induction heating by a high frequency magnetic field of the work coil 70.

The mounting table 90 is a support table for supporting the crucible 10, the crucible stand 20, the reflector 30, the afterheater 40, and the refractories 50 and 60 in the refractory 60. The chamber 100 is a housing that covers the entire chamber including the work coil 70 in addition to the components in the refractory 60 supported by the mounting table 90.

Outside the chamber 100, there is a power supply 110 that supplies power to each component of the work coil 70 and the high-frequency induction heating type single crystal growing device 130, and a control that controls the overall operation of the high-frequency induction heating type single crystal growing device 130. Parts are provided as needed.

Next, the individual components will be described in more detail.

The crucible 10 used in the Cz method is generally selected so that the inner diameter d of the crucible 10 is also changed according to the crystal diameter D to be grown, and D / d = about 0.5 to 0.7. For example, when growing a single crystal having a crystal diameter D of φ110 mm, a crucible 10 having an inner diameter d of about 150 mm to 220 mm is used.

In the Cz method, a single crystal piece to be the seed crystal 140 is brought into contact with the melt surface of the single crystal raw material 150 in the pit 10, and the seed crystal 140 is pulled upward while being rotated by the pulling shaft (seed rod) 80. , A cylindrical single crystal having the same orientation as the seed crystal 140 is grown.

The rotation speed and pulling speed of the seed crystal 140 depend on the type of single crystal to be grown and the temperature environment at the time of growth, and need to be appropriately selected according to these conditions. Further, when growing a single crystal, it is necessary to release the latent heat of solidification generated by the crystallization of the melt at the growth interface upward through the seed crystal 140, so that the temperature gradient (for example,) in which the temperature decreases upward from the growth interface (for example). It is necessary to carry out at 5 ° C./cm). In addition, in order to prevent the shape of the grown single crystal from bending or twisting, a temperature gradient (for example, 3 ° C./cm) in which the temperature rises horizontally from the growth interface toward the crucible wall even in the raw material melt. ) Need to be done below. In order to stabilize the heat convection in the raw material melt, it is advisable to grow the single crystal under a temperature gradient in which the temperature rises in the vertical direction from the growth interface toward the crucible bottom.

When growing an LN single crystal, the melting point of the LN crystal is 1250 ° C., and oxygen is required in the growing atmosphere. Therefore, a crucible made of platinum (Pt) having a melting point of about 1760 ° C. and being chemically stable. 10 is used. The pulling speed at the time of growing is generally about several mm / H, and the rotation speed is about several to several tens of rpm. In addition, the inside of the furnace at the time of growing is generally an atmosphere or a mixed gas atmosphere of nitrogen and oxygen having an oxygen concentration of about 20%. Under such conditions, after growing the single crystal to the desired size, the grown single crystal is separated from the raw material melt by performing operations such as changing the pulling speed and gradually increasing the melt temperature, and then. The single crystal is taken out from the growing furnace after the temperature in the growing furnace becomes close to room temperature by slowly cooling by reducing the power of the growing furnace at a predetermined speed.

The single crystal grown by such a method and taken out from the furnace is subjected to an annealing treatment for removing residual strain caused by a temperature difference in the crystal and a polling treatment for aligning the direction of spontaneous polarization in the crystal. After that, it is handed over to a substrate processing process for slicing, polishing, and the like.

[Raw material charging method]
By the way, when the LN crystal is grown by the Cz method using the growing furnace described in Patent Document 1, the weight of the grown crystal is 50% to 80% at the maximum of the weight of the raw material charged in the Pt crucible. Is. Then, when the next growth is carried out, the raw material amount corresponding to the weight of the grown crystal is charged into the crucible so that the amount of the raw material is the same as that of the previous growth.

When such growth is repeated, if the raw material composition is inappropriate, the Curie temperature will fluctuate not only within the crystals but also between the crystals.

As a result of investigating the relationship between the raw material composition and the Curie temperature of the crystal to be grown in detail, the present inventor has found that the Curie temperature of the single crystal to be grown is 1137.5 ° C or higher and 1139.5 ° C centered on 1138.5 ° C. It was found that when a single crystal is grown using a raw material in which a predetermined amount _{of Li 2} CO ₃ powder and Nb ₂ O ₅ are mixed so as to be within ° C., the fluctuation of the Curie temperature within and between the crystals is the smallest.

That is, when growing a single crystal and growing the next single crystal, the raw materials used are added and supplemented, but in the next growing of the single crystal, a mixed raw material of the remaining raw material and the added raw material is used. Will be used. Therefore, it is inevitable that the overall raw material composition gradually changes as the number of times of growing increases, but the Curie temperature of the grown single crystal is 1137.5 ° C or higher and 1139.5 ° C centered on 1138.5 ° C. By using the mixed raw material adjusted to be within ° C. each time, the fluctuation of the Curie temperature between single crystals can be reduced.

Therefore, in the present invention, a predetermined amount _{of Li 2} CO ₃ powder and Nb ₂ O ₅ is added so that the Curie temperature of the grown single crystal is 1137.5 ° C. or higher and 1139.5 ° C. or lower with the Curie temperature of 1138.5 ° C as the center value. Provided is a method for producing a lithium niobate single crystal, which comprises a step of growing a single crystal using a mixed raw material.

Further, in the present invention, the lithium niobate single crystal grown by the above production method is characterized in that the Curie temperature exceeds 1137 ° C. and is lower than 1140 ° C.

Hereinafter, a detailed description will be given.

As described above, when the LN single crystal is grown by the Cz method using the growth furnace, the crystal growth is repeated. The single crystal is grown in the first growth, and when the next growth is carried out, the raw material 150 corresponding to the weight of the single crystal grown in the first growth is charged in the crucible 10 so that it becomes the same as the previous growth. ing. At this time, the raw material composition is generally the same as the first raw material composition.

FIG. 2 is a survey result showing the relationship between the raw material composition and the Curie temperature of the crystal to be grown. As shown in FIG. 2, the Curie temperature of the crystal tends to be higher when the lithium is rich in the raw material composition and the Curie temperature of the crystal grown from the raw material 150. Therefore, when the Curie temperature of the grown crystal is likely to deviate from the desired range, the Curie temperature can be adjusted by adjusting the raw material composition. That is, if you want to raise the Curie temperature of the single crystal to be grown, increase the mass ratio of lithium in the raw material, and if you want to lower the Curie temperature of the single crystal, lower the mass ratio of lithium in the raw material. Just do it. As the raw material, for example, Li ₂ CO ₃ powder and Nb ₂ O ₅ are mixed in a predetermined amount to obtain the raw material 150.

In the present embodiment, the raw material composition _{of the Li 2} CO ₃ powder and Nb ₂ O ₅ is adjusted so that the Curie temperature of the single crystal is 1137.5 ° C. or higher and 1139.5 ° C. or lower with the Curie temperature of the single crystal as the center value. do. Several methods can be considered as a method for adjusting the raw material composition. _{For example, Li 2} CO ₃ is added to the calcined raw material having the same composition as the previous growth when adjusting the Curie temperature of the single crystal to be grown in the higher direction, and Nb when adjusting in the lower direction. ₂ O ₅ is added. That is, Li ₂ CO ₃ containing Li is added to increase the mass ratio of LI, and Nb ₂ O ₅ containing no Li is added to decrease the mass ratio of Li. The amount of Li ₂ CO ₃ powder and Nb ₂ O ₅ added can be calculated from the relationship between the composition of FIG. 2 and the Curie temperature.

In FIG. 3, the raw material composition is set so that the target Curie temperature of the single crystal after growth is 1137 ° C., 1138 ° C., 1138.5 ° C., 1139 ° C., 1140 ° C., 1141 ° C. to grow the single crystal. Then, it is a figure which showed the change of the Curie temperature when the crystal growth was performed with the same raw material composition as the first time. The Curie temperature was defined as the Curie temperature at the position of the lower portion (bottom portion) of the straight body portion of the grown single crystal. In FIG. 3, the case where the target Curie temperature is 1141 ° C. is shown by the curve A, and the case where the target Curie temperature is 1140 ° C. is shown by the curve B. Similarly, the case where the target Curie temperature is 1139 ° C. is shown by the curve C, and the case where the target Curie temperature is 1138.5 ° C. is shown by the curve D. Further, the case where the target Curie temperature is 1138 ° C. is shown by the curve E, and the case where the target Curie temperature is 1137 ° C. is shown by the curve F.

As shown in FIG. 3, the raw material composition of _{Li 2} CO ₃ powder and Nb ₂ O ₅ so that the target Curie temperature is 1137.5 ° C. or higher and 1139.5 ° C. or lower with the center value of 1138.5 ° C. The Curie temperature exceeds 1137 ° C. and is stable in the range of less than 1140 ° C. in the single crystal that has been repeatedly grown 10 times or more. _{In particular, when the raw material composition of Li 2} CO ₃ powder and Nb ₂ O ₅ is adjusted so that the target Curie temperature exceeds 1138 ° C and falls below 1139 ° C, a single crystal repeatedly grown 10 times or more is Curie. The temperature is stable in the range of 1138 ° C. or higher and 1139 ° C. or lower, which is more preferable. On the other hand, at 1137 ° C. (curve F), the Curie temperature gradually decreases, and at 1140 ° C. (curve B), the Curie temperature gradually increases.

_{In addition, the raw material composition of Li 2} CO ₃ powder and Nb ₂ O ₅ is adjusted and grown so that the target Curie temperature is 1137.5 ° C or higher and 1139.5 ° C or lower with 1138.5 ° C as the center value. The single crystal can suppress the variation in Curie temperature in the single crystal. In the crystal obtained by setting the target Curie temperature to 1137.5 ° C. or higher and 1139.5 ° C. or lower, the difference in Curie temperature between the crystal top portion and the bottom portion is within 0.5 ° C. in the crystal of the first growth. It is stable within 1 ° C at the 10th crystal growth. On the other hand, at 1137 ° C. (curve F), the temperature is lower within 1 ° C. for the first cultivated crystal and 2 ° C. at the bottom side for the 10th cultivated crystal. At 1140 ° C. (curve B), the crystal at the first growth is within 1.0 ° C., and the crystal at the 10th growth is at 2 ° C. on the bottom side, and the variation is large.

When the target Curie temperature is 1137.5 ° C or higher and 1139.5 ° C or lower, the change in Curie temperature is small even if the number of growings increases, and especially when the target Curie temperature is 1138 ° C or higher and 1139 ° C or lower, the growing is performed. It has been shown that the fluctuation of Curie temperature is very small even if the number of times is increased.

[Example]
Hereinafter, examples of the present invention will be specifically described with reference to comparative examples.

[Example 1]
Using the high-frequency induction heating type single crystal growing apparatus shown in FIG. 1, a 128 ° RY-LN crystal having a crystal straight body diameter of φ110 mm was grown using a Pt crucible having an inner diameter of 150 mm.

First, the Pt crucible 10 is charged with LN powder whose composition has been adjusted so that crystals having a Curie temperature of 1138.5 ° C. can be obtained as the raw material 150, the raw material 150 is melted, and then the tip of the seed crystal 140 is crucible. Crystals were grown by immersing in the raw material melt in No. 10. The solidification rate (= crystal weight / raw material charge amount) of the grown crystals was 70%.

In the next growing, a raw material having the same composition as that of the first growing was added to the Pt crucible by the same weight as the crystals obtained in the first growing, and the second growing was performed. The breeding was repeated 10 times in the same procedure.

All of the obtained crystals were sampled from the top and bottom of the crystals, and the Curie temperature was measured using a TG-DTA device. As a result, only variations due to analysis accuracy were observed, and all were 1138.5 ± 0.5. At ° C, no difference in Curie temperature between the top and bottom of the crystal was observed, and no tendency was observed after 10 times of growing.

[Example 2]
A 128 ° RY-LN crystal having a crystal straight body diameter of φ110 mm was repeatedly grown 10 times under the same conditions as in Example 1 except that the target Curie temperature was set to 1139 ° C. When all the obtained crystals were sampled from the top and bottom parts of the crystals and the Curie temperature was measured using a TG-DTA device, the Curie temperature tended to increase as the number of times of growth increased, and the first time. The Curie temperature, which was 1139 ° C. at the bottom portion during growing, became 1139.4 ° C. at the 10th grown crystal. In addition, the Curie temperature difference between the top and bottom of the crystal also tends to increase as the number of repeated growths increases, and the difference of 0.5 ° C in the first growth is the top in the 10th growth crystal. The Curie temperature at the bottom was 1 ° C higher than that at the bottom.

[Example 3]
A 128 ° RY-LN crystal having a crystal straight body diameter of φ110 mm was repeatedly grown 10 times under the same conditions as in Example 1 except that the target Curie temperature was set to 1138 ° C. When all the obtained crystals were sampled from the top and bottom parts of the crystals and the Curie temperature was measured using a TG-DTA device, the Curie temperature tended to decrease as the number of growing times increased, and the first time. The Curie temperature, which was 1138.3 ° C. at the bottom portion during growth, became 1137.7 ° C. at the 10th growth crystal. In addition, the Curie temperature difference between the top and bottom of the crystal also tends to increase as the number of repeated growths increases, and the difference of 0.5 ° C in the first growth is the top in the 10th growth crystal. The Curie temperature at the bottom was 1 ° C lower than that at the bottom.

From Examples 1 to 3, when the Curie temperature of the single crystal actually measured is in the range of 1137.7 ° C. or higher and 1139.4 ° C. or lower, the number of growths of the single crystal may increase, but the Curie temperature is very stable. It has been shown that it is possible to produce crystals.

[Comparative Example 1]
A 128 ° RY-LN crystal having a crystal straight body diameter of φ110 mm was repeatedly grown 10 times under the same conditions as in Example 1 except that the target Curie temperature was set to 1140 ° C. When all the obtained crystals were sampled from the top and bottom parts of the crystals and the Curie temperature was measured using a TG-DTA device, the Curie temperature tended to increase as the number of growing times increased, and the first time. The Curie temperature, which was 1140.2 ° C. at the bottom of the grown crystal, became 1142.6 ° C. in the 10th grown crystal. In addition, the Curie temperature difference between the top and bottom of the crystal also tends to increase as the number of repeated growths increases, and the difference of 1 ° C in the first growth is changed to the top in the 10th growth crystal. On the other hand, the Curie temperature at the bottom was 2 ° C higher.

In Comparative Example 1, the target Curie temperature is set to 1140 ° C., but the actual Curie temperature is 1140.2 ° C. or higher. Therefore, the Curie temperature of less than 1140 ° C. is within the temperature range that effectively functions in the present invention.

[Comparative Example 2]
A 128 ° RY-LN crystal having a crystal straight body diameter of φ110 mm was repeatedly grown 10 times under the same conditions as in Example 1 except that the target Curie temperature was set to 1137 ° C. When all the obtained crystals were sampled from the top and bottom parts of the crystals and the Curie temperature was measured using a TG-DTA device, the Curie temperature tended to decrease as the number of times of growth increased, and the first time. The Curie temperature, which was 1136.8 ° C. at the bottom of the grown crystal, became 1134.3 ° C. in the 10th grown crystal. In addition, the Curie temperature difference between the top and bottom of the crystal also tends to increase as the number of repeated growths increases, and the difference of 1 ° C in the first growth is changed to the top in the 10th growth crystal. On the other hand, the Curie temperature at the bottom was 2 ° C lower.

In Comparative Example 2, the target Curie temperature is set to 1137 ° C., but the actual Curie temperature is 1136.8 ° C. or lower. Therefore, temperatures higher than the Curie temperature of 1137 ° C. are within the temperature range that effectively functions in the present invention.

_{As described above, according to the present embodiment, the Li 2} CO ₃ powder and Nb ₂ O ₅ are used so that the Curie temperature of the single crystal is 1137.5 ° C. or higher and 1139.5 ° C. or lower, centering on 1138.5 ° C. It was shown that by adjusting the raw material composition of the above and growing the single crystal, a high-quality lithium niobate single crystal having a substantially uniform Curie temperature can be formed even if the number of times the single crystal is grown is repeated.

Further, the Curie temperature of the single crystal grown 10 times or more by adjusting the raw material composition of _{Li 2} CO ₃ powder and Nb ₂ O ₅ so that the target Curie temperature exceeds 1138 ° C and becomes less than 1139 ° C has a Curie temperature. It was shown that a high-quality lithium niobate single crystal that is stable in the range of 1138 ° C. or higher and 1139 ° C. or lower and has high Curie temperature uniformity can be formed.

Although the preferred embodiments and examples of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments and examples, and can be applied to the above-mentioned examples without departing from the scope of the present invention. Various modifications and substitutions can be made.

10 Crucible 20 Crucible stand 30 Reflector 40 After heater 50, 60 Refractory 70 Work coil 80 Pull-up shaft 81 Seed holder 90 Mounting stand 100 Chamber 110 Power supply 120 Control unit 140 Seed crystal 150 Raw material

Claims (4)

In a lithium niobate single crystal
A lithium niobate single crystal characterized in that the Curie temperature of the bottom portion of the single crystal exceeds 1137 ° C. and is lower than 1140 ° C. The lithium niobate single crystal according to claim 1, wherein the Curie temperature is 1138 ° C. or higher and 1139 ° C. or lower. In the method for growing a lithium niobate single crystal,
Using a raw material in which a predetermined amount _{of Li 2} CO ₃ powder and Nb ₂ O ₅ are mixed so that the Curie temperature of the single crystal to be grown is 1137.5 ° C or higher and 1139.5 ° C or lower with the Curie temperature of 1138.5 ° C as the center value. A method for producing a lithium niobate single crystal, which comprises a step of growing a single crystal. When the Curie temperature is lower than the target Curie temperature, _{the mass ratio of Li 2} CO ₃ powder is increased, and when the Curie temperature is lower than the target Curie temperature, _{the mass ratio of Nb 2} O ₅ is increased to obtain the Curie temperature. The method for producing a lithium niobate single crystal according to claim 3, wherein the temperature is controlled.

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