JP2009249254A - Method for producing lithium tantalate crystal and lithium tantalate crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium tantalate crystal in which the pyroelectric property is suppressed; and to provide a method for producing the same. <P>SOLUTION: At least a lithium tantalate crystal base material is prepared, and the base material is immersed into a solution containing a metal halide such as sodium chloride or potassium chloride. Thereafter, the base material is heat-treated at a temperature not lower than 310°C and not higher than Curie temperature in a reducing atmosphere in such a state that a reducing agent is disposed near the base material at a distance of ≤20 mm from the base material or the reducing agent and the base material are superposed. At this time, as the reducing agent, multiple polarized lithium tantalate, obtained by heat treating a lithium tantalate crystal at a temperature not lower than Curie temperature in a reducing atmosphere, is used. By this treatment, since the electrical conductivity of the lithium tantalate crystal is enhanced and becomes uniform in crystal plane, the pyroelectric property is suppressed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an improvement in characteristics of lithium tantalate crystals used for applications in which electrical signals are processed by forming a pattern with a metal electrode on a wafer such as a surface acoustic wave device.

  Lithium tantalate is used for applications that utilize electrical characteristics such as surface acoustic wave (SAW) signal processing. Lithium tantalate crystals suitable for this application show the piezoelectric response (piezoelectricity) required for SAW devices due to their crystal structure, but the lithium tantalate crystals available by conventional methods are in addition to piezoelectricity. Cause pyroelectric response (pyroelectricity).

  Piezoelectricity of lithium tantalate crystals is an indispensable characteristic when using lithium tantalate crystals as SAW devices. On the other hand, pyroelectricity is applied to the outer surface of the crystal by changing the temperature of the lithium tantalate crystal. It is observed as a surface charge that is generated and charges the crystal. This surface charge is considered to cause a spark discharge between metal electrodes formed on a wafer made of lithium tantalate crystals when using the lithium tantalate crystals as a SAW device, causing a significant performance defect of the SAW device. ing.

  For this reason, in designing a SAW device using a lithium tantalate crystal, a device that does not generate surface charges, a device that releases generated surface charges, or a device that widens the interval between metal electrodes is required. In order to adopt this, there is a disadvantage that the design of the SAW device itself is restricted.

  In addition, in the manufacturing process of SAW devices using lithium tantalate crystals, there are processes in which heat is applied to the lithium tantalate crystals in processes such as vapor deposition of the metal film and removal of the resist. When applied to the lithium acid crystal, charge is generated on the outer surface due to the pyroelectric property of the lithium tantalate crystal. This surface charge causes a spark discharge between the metal electrodes, resulting in destruction of the electrode pattern. Therefore, the SAW device manufacturing process is devised so as not to change the temperature as much as possible, or the temperature change is moderated. As a result of these measures, there are disadvantages such as a reduction in the throughput of the manufacturing process or a narrow margin for guaranteeing the performance of the SAW device.

  In the lithium tantalate crystal produced by the usual method, the charge on the outer surface generated by pyroelectricity is neutralized by free charge from the surrounding environment and disappears over time, but this disappearance time is several hours or more In the SAW device manufacturing process, this spontaneous pyroelectricity cannot be expected.

  For applications such as SAW devices, there is a need for a piezoelectric crystal that maintains the piezoelectricity required to exhibit device characteristics and that does not generate charge on the outer surface of the crystal due to the above background. There is a need for lithium tantalate crystals that do not show surface charge accumulation for such applications.

  As a method for producing a lithium tantalate crystal with reduced surface charge, the lithium tantalate crystal is exposed to a reducing atmosphere at 500 ° C. or higher to increase the conductivity, and the surface charge generated by pyroelectricity can be quickly neutralized or A method of extinction is disclosed (see Patent Document 1).

  However, when the lithium tantalate crystal is reduced by such a method, the Curie point of the lithium tantalate crystal is about 603 ° C., so that the piezoelectricity is lost when exposed to a high temperature exceeding this. Moreover, when it heat-processes at a comparatively low temperature of about 400-600 degreeC, it is not fully reduced. That is, it is difficult for the heat treatment in the reducing gas described in Patent Document 1 to improve the conductivity without deteriorating the piezoelectricity of the lithium tantalate crystal.

Further, a method of reducing lithium tantalate crystals under reduced pressure using an alkali metal compound, particularly a lithium compound, as a reducing agent has been disclosed (see Patent Document 2).
There is an explanation that the lithium compound binds to oxygen in the lithium tantalate wafer and is released in the form of lithium oxide, and since it has a role as a reducing agent, it is stated that it is better to increase the concentration when applying. ing.

  However, there is a description that organic solvents such as polyvinyl alcohol and glycerin are suitable when applied at a high concentration, but such a method is sticky and contaminates the inside of the furnace, so there is a problem in terms of productivity. is there.

Also disclosed is a method in which a reduction heat treatment is performed at 300 to 600 ° C. by bringing a lithium tantalate crystal, etc., which has undergone a reduction treatment at a high temperature (700 ° C. or more) and turned black into contact with or close to the lithium tantalate crystal as a raw material (See Patent Document 3).
However, the electrical conductivity of the lithium tantalate crystals produced by this method varies within the plane, and there is room for improvement in this regard.
JP-A-11-92147 JP 2005-314137 A WO2004 / 079061

  The present invention has been made in view of the above-described problems, and is generated by changing the temperature of a lithium tantalate crystal by improving conductivity and making the improved conductivity uniform within the crystal plane. It is an object of the present invention to provide a method for producing a lithium tantalate crystal capable of suppressing pyroelectricity, and a lithium tantalate crystal.

  To achieve the above object, according to the present invention, there is provided a method for producing a lithium tantalate crystal, comprising at least preparing a lithium tantalate crystal material and immersing the material in a solution containing a metal halide. A method for producing a lithium tantalate crystal, characterized by heat-treating a reducing agent and the lithium tantalate crystal material close to each other at a distance of 20 mm or less in a reducing atmosphere at a temperature of 310 ° C. or more and a Curie temperature or less. (Claim 1).

  In this way, at least a lithium tantalate crystal material is prepared, and after immersing the material in a solution containing a metal halide, the reducing agent and the above are at a temperature of 310 ° C. or higher and a Curie temperature or lower and in a reducing atmosphere. If the lithium tantalate crystal material is heat-treated close to a distance of 20 mm or less, the conductivity is improved and the conductivity is uniform in the crystal plane, and the lithium tantalate crystal that can suppress pyroelectricity Can be manufactured.

  Further, in the present invention, a method for producing a lithium tantalate crystal, at least preparing a lithium tantalate crystal material, immersing the material in a solution containing a metal halide, and at least 310 ° C. and a Curie temperature or less A method for producing a lithium tantalate crystal is provided, in which a reducing agent and the lithium tantalate crystal material are superposed and heat-treated at a temperature of 5 ° C. in a reducing atmosphere (claim 2).

  In this way, at least a lithium tantalate crystal material is prepared, and after immersing the material in a solution containing a metal halide, the reducing agent and the above are at a temperature of 310 ° C. or higher and a Curie temperature or lower and in a reducing atmosphere. Producing a lithium tantalate crystal capable of suppressing pyroelectricity with improved conductivity and uniform conductivity in the crystal plane when the lithium tantalate crystal material is superposed and heat-treated. Can do.

At this time, as the reducing agent, polypolarized lithium tantalate obtained by heat-treating lithium tantalate crystals at a temperature equal to or higher than the Curie temperature and in a reducing atmosphere can be used.
As described above, if the multipolar lithium tantalate obtained by heat-treating the lithium tantalate crystal at a temperature equal to or higher than the Curie temperature and in a reducing atmosphere is used as the reducing agent, the lithium tantalate crystal as a product is obtained. It can be manufactured without contamination. Moreover, it can be set as the reducing agent which has sufficient reducibility, and is preferable.

At this time, sodium chloride or potassium chloride can be used as the metal halide.
Thus, if sodium chloride or potassium chloride is used as the metal halide, the conductivity of the solution can be increased, the effect of improving the conductivity of the lithium tantalate crystal to be produced is increased, and the conductivity in the crystal plane is increased. The effect of making the rate uniform can be exhibited. In addition, these have an advantage that high-purity and inexpensive products can be easily obtained.

At this time, an atmospheric gas containing hydrogen gas can be used as the reducing atmosphere.
Thus, if an atmosphere gas containing hydrogen gas is used as the reducing atmosphere, the reduction treatment of the lithium tantalate crystal can be performed quickly.

At this time, the concentration of the solution containing the metal halide can be 0.001 mol / l or more and 1.0 mol / l or less (Claim 6).
As described above, if the concentration of the solution containing the metal halide is 0.001 mol / l or more and 1.0 mol / l or less, the lithium tantalate crystal material may stick to the solution and contaminate the inside of the furnace. In addition, it is possible to prevent deposits from appearing on the surface of the material after the water has evaporated.

In addition, according to the present invention, there is provided a lithium tantalate crystal that is manufactured using the manufacturing method according to the present invention and has improved conductivity and conductivity is uniform within the crystal plane. .
Thus, if the lithium tantalate crystal has improved conductivity and conductivity is uniform in the crystal plane, the conductivity is sufficiently improved and the conductivity is uniform in the crystal plane. The material has a property that the accumulation of charges on the crystal surface caused by temperature change is substantially not observed, and is a material that is extremely advantageous in the manufacture of SAW devices.

  In the present invention, in the production of a lithium tantalate crystal, at least a lithium tantalate crystal material is prepared, immersed in a solution containing a metal halide, and reduced at a temperature of 310 ° C. or higher and a Curie temperature or lower. In the atmosphere, the reducing agent and the lithium tantalate crystal material are heat-treated close to each other at a distance of 20 mm or less, or at least a lithium tantalate crystal material is prepared, and the material is converted into a solution containing a metal halide. After the immersion, heat treatment is performed by superposing the reducing agent and the lithium tantalate crystal material at a temperature of 310 ° C. or higher and lower than the Curie temperature and in a reducing atmosphere, so that the conductivity is improved and the conductivity is increased on the crystal plane. It is possible to produce a lithium tantalate crystal that is uniform and can suppress pyroelectricity.

Hereinafter, although an embodiment is described about the present invention, the present invention is not limited to this.
Conventionally, lithium tantalate crystals have been used as a material for SAW devices. And this lithium tantalate crystal has the characteristic that the generation | occurrence | production (pyroelectricity) of an electric charge is not seen in the crystal outer surface, maintaining the piezoelectricity required in order to exhibit a SAW device characteristic. Things are required.

In order to manufacture such a lithium tantalate crystal, a method based on the principle of suppressing pyroelectricity by improving the conductivity of the lithium tantalate crystal is disclosed.
However, even if a lithium tantalate crystal is manufactured using such a conventional method, the conductivity becomes non-uniform in the plane of the crystal, and the effect of suppressing pyroelectricity cannot be stably obtained. There was a problem.

  Therefore, the present inventor has intensively studied to solve such problems. As a result, before the reduction treatment of the lithium tantalate crystal material, if the material is immersed in a solution with high conductivity and ions are attached to the surface of the lithium tantalate crystal material, the surface is stabilized. The present inventors completed the present invention by conceiving that the effect of improving the conductivity after the treatment can be enhanced and the variation in conductivity within the crystal plane can be suppressed.

FIG. 1 shows a flow chart of the method for producing a lithium tantalate crystal of the present invention.
In the method for producing a lithium tantalate crystal of the present invention, first, a lithium tantalate crystal material that is a base material is prepared (FIG. 1A). This can be done, for example, as follows.
First, lithium carbonate and tantalum pentoxide are weighed and mixed, and the lithium tantalate polycrystal obtained by heating to 1000 ° C. or higher in an electric furnace is put into a noble metal crucible such as iridium. Then, the polycrystal is heated and melted in an atmosphere gas in which a slight amount of high-purity oxygen is mixed with high-purity nitrogen, and then the seed crystal is dipped in the melt, so that rotation is pulled up (so-called Czochralski). Method) to grow a crystal to obtain a lithium tantalate crystal rod.

  The thus obtained lithium tantalate crystal rod is cut into slices using a cutting device, and lapping is performed, whereby a double-sided wrap wafer that is the lithium tantalate crystal material of the present invention can be obtained.

Next, the lithium tantalate crystal material obtained as described above is immersed in a solution containing a metal halide (FIG. 1B).
Thus, if the lithium tantalate crystal material is immersed in a solution containing a metal halide, the solution containing the metal halide has high conductivity and contains various cations and anions. When the surface charge of the lithium crystal material is positive, an anion is attached to the surface, and when it is negative, a cation is attached to the surface. As a result, the surface of the lithium tantalate crystal material is stabilized, and the lithium tantalate crystal after the reduction treatment is stabilized. The conductivity can be improved and the conductivity in the crystal plane can be made uniform.

At this time, sodium chloride or potassium chloride can be used as the metal halide.
Thus, if sodium chloride or potassium chloride is used as the metal halide, the conductivity of the solution can be increased, the effect of improving the conductivity of the lithium tantalate crystal to be produced, and the conductivity in the crystal plane is increased. The effect of uniforming can be exhibited. Moreover, these can be easily obtained at low cost and with high purity.
Other possible inclusions include substances that increase the conductivity of the solution, such as magnesium chloride, aluminum chloride, zinc chloride, etc., and if such substances are used, similar effects are expected. be able to.

Next, a reducing agent used for reducing the lithium tantalate crystal material is prepared (FIG. 1C).
In the present invention, multipolar lithium tantalate obtained by heat-treating a lithium tantalate crystal at a temperature equal to or higher than the Curie temperature and in a reducing atmosphere can be used as the reducing agent.
As described above, if multipolar lithium tantalate obtained by heat-treating a lithium tantalate crystal at a temperature equal to or higher than the Curie temperature and in a reducing atmosphere is used as the reducing agent, a product is obtained by a heat treatment as a subsequent step. Heat treatment can be performed without contaminating the lithium tantalate crystal. Moreover, it can be set as the reducing agent which has sufficient reducibility, and is preferable.

Such a multipolar lithium tantalate crystal can be obtained, for example, as follows.
First, one side of the lithium tantalate crystal material (double-sided lapped wafer) obtained as described above is polished to obtain a colorless translucent polished wafer. Then, the polished wafer is placed in a furnace made of a metallic chamber, and is heat-treated at a temperature equal to or higher than the Curie temperature and in a hydrogen atmosphere.

Here, the atmosphere of the heat treatment for obtaining the reducing agent can be, for example, 100% hydrogen. The heat treatment temperature can be about 1000 ° C. and the heat treatment time can be about 10 hours, for example. However, it is not particularly limited to these.
By performing the heat treatment in this way, the target multipolar lithium tantalate can be obtained.

Next, as shown in FIG. 3, the reducing agent 2 and the lithium tantalate crystal material 1 obtained as described above are brought close to each other so that the distance is 20 mm or less, for example, on a boat made of quartz. Are alternately arranged in a furnace 3 as shown in FIG.
Then, the disposed lithium tantalate crystal material 1 is heat treated together with the reducing agent 2 at a temperature of 310 ° C. to the Curie temperature and in a reducing atmosphere (FIG. 1D).

  Thus, if the reducing agent 2 and the lithium tantalate crystal material 1 are heat-treated close to each other so that the distance between them is 20 mm or less, the reducing effect of the reducing agent 2 can be reliably achieved, and the tantalum obtained. The conductivity of the lithium acid crystal can be reliably increased.

  Here, the closer the distance between the reducing agent 2 and the lithium tantalate crystal material 1 is, the higher the reduction effect of the reducing agent can be. However, the reducing agent 2 and the lithium tantalate crystal material 1 are overlapped as described later. Or, by separating a very small distance, a part of the surface of both of them is in contact, and another part is not in contact, so that the conductivity in the lithium tantalate crystal plane becomes uneven. Can be prevented. Here, the distance slightly separated is not limited to this, but can be, for example, 0.1 mm or more.

Alternatively, when the lithium tantalate crystal material is arranged in the furnace, as shown in FIG. 4, the reducing agent 2 and the lithium tantalate crystal material 1 are overlapped and arranged in the furnace 3 as shown in FIG. You can also
Then, the disposed lithium tantalate crystal material 1 is heat treated together with the reducing agent 2 at a temperature of 310 ° C. to the Curie temperature and in a reducing atmosphere (FIG. 1D).

  Thus, after the lithium tantalate crystal material is immersed in a solution containing a metal halide, the reducing agent and the lithium tantalate crystal material are 20 mm in a reducing atmosphere at a temperature of 310 ° C. or higher and a Curie temperature or lower. The tantalum lithium crystal material is immersed in a solution containing a metal halide, at a temperature of 310 ° C. or higher and a Curie temperature or lower, and in a reducing atmosphere, and the reducing agent and the tantalum. If lithium acid crystal material is superposed and heat-treated, lithium tantalate crystal having high conductivity can be produced even at a relatively low temperature below the Curie temperature, and the conductivity should be uniform in the crystal plane. Can do. That is, it is possible to manufacture a lithium tantalate crystal that can suppress pyroelectricity while maintaining the piezoelectricity required to exhibit device characteristics such as a SAW device.

At this time, an atmosphere gas containing hydrogen gas can be used as a reducing atmosphere during the reductive heat treatment.
Thus, if an atmosphere gas containing hydrogen gas is used as the reducing atmosphere, the reduction treatment of the lithium tantalate crystal can be performed quickly.

At this time, the concentration of the solution containing the metal halide can be 0.001 to 1.0 mol / l.
Thus, when the concentration of the solution containing the metal halide is 0.001 to 1.0 mol / l, the lithium tantalate crystal material is not sticky by the solution and contaminates the furnace, It is possible to prevent deposits from appearing on the surface of the material after the water has evaporated.

  Thus, according to the present invention, the lithium tantalate crystal manufactured using the manufacturing method according to the present invention has sufficiently improved conductivity, and the conductivity is uniform in the plane, so that the piezoelectricity is maintained. However, it has a characteristic that the accumulation of charges on the crystal surface caused by a temperature change is substantially not observed, and is a material that is extremely advantageous in the manufacture of SAW devices.

Here, the conductivity can be measured as follows. That is, the electrical conductivity is the reciprocal of the volume resistivity, but the volume resistivity can be obtained from the resistance value measured using a measuring instrument such as Hewlett Packard's 4329A High Resistance Meter and 16008A Resistivity by the following equation: it can.
ρ = (πd ² / 4t) · R
ρ: Volume resistivity (Ω · cm)
π: Circumference d: Center electrode diameter (cm)
t: LT wafer thickness (cm)
R: Resistance value (Ω)
In this case, for example, a voltage of 500 volts is applied, and in order to obtain a stable measurement value, the resistance value one minute after applying the voltage may be measured.

  As described above, in the present invention, in the production of lithium tantalate crystals, at least a lithium tantalate crystal material is prepared, and after immersing the material in a solution containing a metal halide, a temperature of 310 ° C. or higher is set at a Curie temperature. The reducing agent and the lithium tantalate crystal material are heat-treated at a distance of 20 mm or less in a reducing atmosphere at the following temperature, or at least a lithium tantalate crystal material is prepared, and the material is made of a metal halogen After being immersed in a solution containing a chemical compound, the reducing agent and the lithium tantalate crystal material are superposed and heat-treated at a temperature of 310 ° C. or higher and a Curie temperature or lower and in a reducing atmosphere, so that the conductivity is improved, and Lithium tantalate crystals that have uniform conductivity in the crystal plane and can suppress pyroelectricity can be produced. .

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples of the present invention, but the present invention is not limited to these.

Example 1
Using the production method of the present invention, a lithium tantalate crystal is produced as follows, and the obtained lithium tantalate crystal surface is measured for the presence or absence of color unevenness, the color difference, and the conductivity. Asked and evaluated them.
First, a lithium tantalate crystal material was prepared as follows.
A lithium tantalate crystal rod with a diameter of 100 mm and a length of 50 mm turned by 36 ° rotation in the y direction with respect to the surface normal is pulled up by the Czochralski method, and the crystal is cut by a processing device, sliced, and wrapped Processing was performed to obtain a double-sided lapped wafer having a thickness of 0.3 mm as a lithium tantalate crystal material.

Next, a polycrystalline lithium tantalate crystal was prepared as a reducing agent as follows.
One side of the double-sided wrap wafer obtained as described above is polished to obtain a polished wafer having a thickness of 0.25 mm. The polished wafer is placed in a furnace made of a metal chamber, and is 100% hydrogen and 1050 ° C. A polycrystalline lithium tantalate crystal was obtained by treatment in an atmosphere for 10 hours.

On the other hand, a sodium chloride solution having a concentration of 0.001 to 1.0 mol / l shown in Table 1 was prepared, and the lithium tantalate crystal material as a raw material was immersed in the sodium chloride aqueous solution for 15 minutes, and then dried. .
Next, as shown in FIG. 3, the lithium tantalate crystal material and the polycrystalline lithium tantalate crystal as the reducing agent are alternately arranged on a quartz boat, and the distance between them is set to 3.0 mm. It was placed in a furnace consisting of a metallic chamber as shown.

  Then, while flowing hydrogen at a rate of about 1.5 liters per minute under normal pressure, the temperature was raised from room temperature to 500 ° C. at a rate of about 6.7 ° C. per minute, and after holding for 6 hours, about 6. The temperature was lowered at a rate of 7 ° C., the atmosphere was introduced when the temperature in the furnace was 250 ° C. or lower, and the lithium tantalate crystal was taken out of the furnace when the temperature was further 30 ° C. or lower.

Here, the measurement of the color unevenness and the color difference was performed as follows.
The color unevenness was measured by visual inspection, and the color difference was measured with a NF333 spectrophotometer manufactured by Nippon Denshoku Co., Ltd., as the value of brightness L * in the L * a * b * color system defined by JIS Z8729. The color difference can be regarded as color unevenness quantified numerically by the measurement method.
Further, the variation in conductivity was obtained by the following equation.
{(Max conductivity−Min conductivity) / Average} × 100

  The results are shown in Table 1. As shown in Table 1, it was confirmed that the conductivity value was larger than that of Comparative Example 1 described later, and the variation in conductivity and color difference in the crystal plane was improved and uniformized. Moreover, it turns out that the variation of electrical conductivity and a color difference is improved and it is made uniform, so that the density | concentration of sodium chloride becomes large.

(Example 2)
A lithium tantalate crystal was produced under the same conditions as in Example 1 except that the concentration of sodium chloride was 0.1 mol / l and the reduction treatment temperature was 450 ° C. and 550 ° C., and the same evaluation as in Example 1 was performed. went.
The results are shown in Table 1. As shown in Table 1, it was confirmed that variation in conductivity and color difference in the crystal plane was improved and uniformed as compared with Comparative Example 1 described later.

(Example 3)
A lithium tantalate crystal was produced under the same conditions as in Example 2 except that the reducing agent and the lithium tantalate crystal material at the time of the reduction treatment were superposed and disposed in the furnace as shown in FIG. The same evaluation was performed.
The results are shown in Table 1. As shown in Table 1, as compared with Comparative Example 1, it was confirmed that variation in conductivity and color difference in the crystal plane was improved and uniformized.

(Examples 4 to 6)
Lithium tantalate crystals were produced under the same conditions as in Examples 1 to 3, except that a potassium chloride solution was used as the halide contained in the solution to immerse the lithium tantalate crystal material before the reduction treatment, evaluated.
The results are shown in Table 2. As shown in Table 2, as compared with Comparative Example 1, it was confirmed that the variation in conductivity and color difference in the crystal plane was improved and uniformized.

(Comparative Example 1)
Except for omitting the step of immersing the lithium tantalate crystal material before the reduction treatment in the solution, lithium tantalate crystals were produced under the same conditions as in Example 1 and evaluated in the same manner.
The results are shown in Table 1. Compared with the examples of the present invention, it was confirmed that the variation in conductivity within the crystal plane was large.

(Comparative Example 2)
A lithium tantalate crystal was produced under the same conditions as in Example 1 except that the distance between the reducing agent and the lithium tantalate crystal material was 25 mm when placed in the furnace, and the same evaluation as in Example 1 was performed. went.
The results are shown in Table 1. As shown in Table 1, since the proximity distance was too far away, the reduction effect of the reducing agent was reduced, and it was confirmed that the conductivity was lower than that of the lithium tantalate crystal produced by the production method of the present invention. It was.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. Are included in the technical scope.

It is a flowchart of the manufacturing method of the lithium tantalate crystal based on this invention. It is the schematic of the furnace which can be used at the time of reductive heat processing with the manufacturing method of the lithium tantalate crystal which concerns on this invention. It is explanatory drawing which shows a mode that the reducing agent and the lithium tantalate crystal material were made to adjoin, when performing reduction heat processing with the manufacturing method of the lithium tantalate crystal which concerns on this invention. It is explanatory drawing which shows a mode that the reducing agent and the lithium tantalate crystal raw material were piled up when performing reduction heat processing with the manufacturing method of the lithium tantalate crystal which concerns on this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Lithium tantalate crystalline material, 2 ... Reducing agent, 3 ... Furnace.

Claims (7)

  A method for producing a lithium tantalate crystal, comprising at least a lithium tantalate crystal material, dipping the material in a solution containing a metal halide, and at a temperature of 310 ° C. or higher and a Curie temperature or lower and a reducing atmosphere A method for producing a lithium tantalate crystal, comprising: heat-treating the reducing agent and the lithium tantalate crystal material close to each other at a distance of 20 mm or less.   A method for producing a lithium tantalate crystal, comprising at least a lithium tantalate crystal material, dipping the material in a solution containing a metal halide, and at a temperature of 310 ° C. or higher and a Curie temperature or lower and a reducing atmosphere A method for producing a lithium tantalate crystal, comprising: superposing a reducing agent and the lithium tantalate crystal material on top of each other and performing a heat treatment.   3. The polypolarized lithium tantalate obtained by heat-treating lithium tantalate crystals at a temperature equal to or higher than the Curie temperature and in a reducing atmosphere as the reducing agent is used. Method for producing lithium tantalate crystals.   The method for producing a lithium tantalate crystal according to any one of claims 1 to 3, wherein sodium chloride or potassium chloride is used as the metal halide.   The method for producing a lithium tantalate crystal according to any one of claims 1 to 4, wherein an atmosphere gas containing hydrogen gas is used as the reducing atmosphere.   6. The lithium tantalate crystal according to claim 1, wherein the concentration of the solution containing the metal halide is 0.001 mol / l or more and 1.0 mol / l or less. Manufacturing method. A lithium tantalate crystal manufactured using the manufacturing method according to any one of claims 1 to 6, wherein the conductivity is improved and the conductivity is uniform in a crystal plane.

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