JPH09188597A - Production of oxide single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for the production of an oxide single crystal effective for preventing the generation of cracks and the inclusion of foreign materials in the single crystal in the case of producing a single crystal expressed by the formula Pb (B<1> , B<2> )1-x Tix }O3 and suppressing the generation of crack in an oscillator even after the polarization treatment. SOLUTION: This oxide single crystal is composed of a composite perovskite compound expressed by the formula Pb (B<1> , B<2> )1-x Tix }O3 ((x) is 0-0.55; B1 is Zn, Mg, Ni, Sc, Yb or In; B2 is Nb or Ta) and having a sintered density corresponding to >=99% of the theoretical density. The smooth surface of a sintered ceramic material 2 having one smooth surface is brought into contact with the smooth surface of a seed single crystal 1 having one smooth surface and having a lattice constant falling within ±10% of the lattice constant of the sintered ceramic material 2 and the contacted material is heated in a closed vessel 5 in a lead atmosphere at 1000-1450 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an oxide single crystal material, and more particularly to a method for producing an oxide single crystal preferably used as a piezoelectric material or a dielectric material.

[0002]

2. Description of the Related Art Lead magnesium niobate, Pb (Mg
_1/3 Nb _2/3 ) O ₃ (PMN) and Pb (In _1/2 N
b _1/2 ) O ₃ and other composite perovskite compounds, which are generally called relaxors, are added to lead titanate, lead silconate, etc. as a dielectric material (USP 4, US Pat. 818,736)
Widely used as a material for piezoelectric actuators. In addition, these single crystal materials are also used for optical applications (USP
3,453,561) and medical piezoelectric single crystal (USP 5,4).
02, 791).

Since the single crystals of these materials are excellent in their optical characteristics, piezoelectric characteristics, dielectric characteristics, etc., their future application is expected. In particular, in the fields of medical equipment and nondestructive inspection machines, when these single crystal materials are used as ultrasonic piezoelectric vibration materials, it is expected that the resolution and sensitivity will be significantly improved. In these devices, an ultrasonic probe is used as a transducer for transmission / reception in order to image the internal state of an object. Examples of the ultrasonic imaging device using such an ultrasonic probe include a medical diagnostic device for inspecting the inside of a human body and an inspection device for detecting flaws inside a metal weld.

Conventionally, a piezoelectric ceramic material called lead zircon titanate (PZT) has been used in these devices for ultrasonic probes.
There has been little improvement over the years, and new materials have been searched for. Therefore, recently, Pb [(B ¹ , B ² ) _1-x
A piezoelectric single crystal composed of a binary system represented by Ti _x ] O ₃ is attracting attention as a candidate for a new material. Where B
¹ is at least one selected from Zn, Mg, Ni, Sc, In and Yb, B ² is selected from at least one of Nb or Ta, and lead titanate is 0 to 55.
It is a piezoelectric single crystal material in the range of mol%. In this perovskite compound, 10 mol% or less of lead is Ba, S
It may be substituted with at least one selected from r, Ca and La.

When a single crystal made of the perovskite compound as described above is used, the vibrator becomes thin even at a low frequency where a high-sensitivity signal can be obtained. When cutting the vibrator into an array, the blade of the dicing machine is cut. The shallow depth enables vertical cutting even with a thin blade thickness. For this reason, it is possible to provide an ultrasonic probe with improved manufacturing yield and reduced side lobes. further,
Since the above-mentioned perovskite compound has a relative dielectric constant equal to or higher than that of the conventional PZT-based piezoelectric ceramic,
Matching with the transmitter / receiver circuit has been improved, and high-sensitivity signals with reduced loss due to cables and device stray capacitance have been obtained.

An ultrasonic probe using these single-crystal ultrasonic vibrators can obtain a highly sensitive signal of 5 dB or more, as compared with an ultrasonic probe using a conventional PZT piezoelectric ceramic. Therefore, in the case of the B-mode image, it is possible to obtain a high-resolution image in which small lesions and voids due to physical changes can be clearly seen down to the deep part. Also,
In the case of the Doppler mode capable of obtaining a CFM image or the like, a large signal can be obtained even from a reflection echo from a minute blood cell having a diameter of about several μm.

As described above, when an ultrasonic probe driven at a low frequency is manufactured by using the above-mentioned single crystal, a thin single crystal can be used, and a strip-shaped vibrator can be cut with high dimensional accuracy even with a thin blade. . As a result, the yield in terms of processing accuracy was improved, and it became possible to suppress the decrease in sensitivity and the increase in sidelobe level.

[0008]

However, Pb
Solid solution type single crystals such as {(B ¹ , B ² ) _1-x Ti _x } O ₃ are apt to have foreign substances, cracks, or scratches inside them, and therefore, when they are produced as an oscillator for an ultrasonic probe. Must avoid these defective areas. Although the standard size required for a transducer for a heart probe for an ultrasonic diagnostic apparatus is 15 mm × 15 mm × 0.4 mm, vibration of this shape is used to cut out a region such as a foreign substance inside a crystal. The current situation is that the production yield of offspring is extremely poor.

Further, there is a problem that cracks are generated in the vibrator when electrodes are formed on such a vibrator and then a polarization treatment is performed by applying a DC voltage. In most cases, the cracks of the vibrator are as large as 50%, which causes a serious obstacle to mass production of the vibrator.

Therefore, an object of the present invention is to solve the above problems by producing a single crystal represented by Pb {(B ¹ , B ² ) _1-x Ti _x } O ₃ . It is an object of the present invention to provide a method for producing an oxide single crystal in which cracks and foreign matter are less likely to be taken in and the crack does not occur in the oscillator even after polarization.

[0011]

As a result of earnest studies, the present inventors have found that foreign matter, cracks, etc. inside the single crystal represented by Pb {(B ¹ , B ² ) _1-x Ti _x } O ₃ are It has been found that this occurs due to the manufacturing method. Conventionally, these single crystals use a flux whose main component is lead oxide,
It was manufactured at a high temperature by the flux method, the kiloporous method, the Bridgman method, the floating zone method, or the like. Therefore, cracks, flux, and foreign substances having a pyrochlore structure are likely to occur inside the obtained single crystal, making it difficult to obtain a large single crystal.

Therefore, it was considered that producing a single crystal without using a flux is an effective method for obtaining a uniform single crystal having no cracks or the like inside, and the present invention was accomplished.

That is, the present invention is a ceramic sintered body represented by the following general formula (1), composed of a composite perovskite compound having a sintered density of 99% or more of the theoretical density and having at least one smooth surface. And a smooth surface of a seed single crystal having a lattice constant within ± 10% of the lattice constant of this ceramics sintered body and at least one surface of which is smooth, And a step of heating the ceramics sintered body and the seed single crystal which are brought into contact with each other in a lead container in a lead atmosphere at a temperature of 1000 to 1450 ° C., a method for producing an oxide single crystal.

Pb {(B ¹ , B ² ) _1-x Ti _x } O ₃ General formula (1) (In the general formula (1), x is a value of 0 or more and 0.55 or less, and B ¹ is Zn, Mg, Ni, Sc, Yb and In
B ² is Nb or Ta. ) Hereinafter, the manufacturing method of the present invention will be described in detail.

The ceramic sintered body used in the method for producing an oxide single crystal of the present invention is the composite perovskite compound represented by the above general formula (1). When the sintered density of this perovskite compound is less than 99% of the theoretical density, a uniform single crystal cannot be obtained, and when an electrode is formed on the surface of the obtained crystal and subjected to polarization treatment, Cracks are likely to occur.

In the general formula (1), when x exceeds 0.55, the obtained crystal is extremely liable to be broken by polarization, and the insulation resistance of the obtained single crystal is lowered to make polarization difficult. When B ¹ and B ² are other than the above-mentioned elements, it becomes difficult to obtain a single crystal material exhibiting piezoelectric characteristics superior to those of PZT ceramics.

The above perovskite compound has a ratio of A site to B site (A / B) of 1.0 when expressed as ABO _3.
It is preferably 0 or more and 1.10 or less. A and B are Pb and {(B ¹ , B ² ) _1-x T, respectively.
i _x }. When (A / B) is less than 1.00, the growth rate of a single crystal is extremely slow, which is not practical.
When (A / B) exceeds 1.10, the lead oxide, which is an extra A-site component, is likely to be contained inside the single crystal.
Further, these excess lead oxides can be supplied from a material such as lead zirconate which is a lead oxide supply source placed inside the sealed container.

In the above-mentioned composite perovskite compound, a part of lead can be replaced with any one of Ba, Sr, Ca and La. In this case, the growth rate of the single crystal becomes extremely slow. In order to avoid it, the substitution ratio is preferably 10 mol% or less of lead.

Such a composite perovskite compound contains Mn, Co, Fe, Sb, W, Cu and H which are transition metals.
f etc .; lanthanide element; or a small amount of alkali metal may be included. In addition, in order to maintain a large piezoelectric constant, the content of these is preferably 1 mol% or less at the maximum.

B ¹ element and B ² in the above general formula (1)
The ratio with the element is usually a value determined by the stoichiometric ratio ± 0.02
Although it is a degree, it is possible to shift this ratio at a rate of about ± 0.2.

In the above perovskite compound, SiO
₂ , Al ₂ O ₃ , B ₂ O ₃ , PtO, MgO, Fe ₂ O
₃ , and additives such as Bi ₂ O ₃ may be contained. In this case, the content of SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ and PtO is preferably 0.5 mol% or less, and the content of other additives is 1 mol% or less. Is preferred. When the content of impurities exceeds this range, crystals of pyrochlore having a low dielectric constant are likely to be generated in addition to the crystals of perovskite, and the number of defects in the crystals increases.

The perovskite compound may further contain ZrO ₂ in an amount of 5 mol% or less. This is because if the proportion of ZnO ₂ exceeds 5 mol%, the growth rate of the single crystal is extremely reduced, and further the compositional variation within the crystal increases.

In addition to the normal sintering described above, the ceramic sintered body can be produced by hot isostatic pressing (HIP) or hot pressing. By using such a method, a sintered body having a sintered density of 99% or more of the theoretical density can be easily obtained.

The size of the ceramic sintered body used in the present invention can be appropriately selected according to the intended use of the single crystal. For example, for a medical ultrasonic probe, it may be about 15 × 15 to 17 × 0.5 mm ³ . The smooth surface of this ceramic sintered body has a smoothness ±
It is preferably about 1.0 μm, and most preferably mirror-polished.

The lattice constant of the ceramics sintered body is
Usually, it is about 3.88 to 4.15 angstrom.
The seed single crystal used in the manufacturing method of the present invention is not particularly limited as long as it has a lattice constant of ± 10% or less from the lattice constant of the above-mentioned ceramic sintered body, and any single crystal is used. be able to. Further, the metal formed on the single crystal has the property of being oriented according to the orientation of the underlying single crystal,
You may form these metals in the middle. Usually, Pt or the like is used as the metal. When a seed single crystal having a lattice constant difference of more than 10% is used, cracking is likely to occur when the obtained single crystal is polarized. In this case, 10
It becomes difficult to manufacture a single crystal having a size of mm or more. The difference between the lattice constant of the ceramic sintered body and the lattice constant of the seed single crystal is preferably small, and the lattice constant is most preferably the same in order to suppress mutual diffusion of the components.

The seed single crystal used in the method of the present invention may be made of a material (for example, MgO or SrTiO ₃ ) which is completely different from the ceramic sintered body, as long as the condition of the lattice constant is satisfied. However, it is preferable that the composition of the seed single crystal is the same as that of the ceramic sintered body, because cracks are less likely to occur when the single crystal having a size of 20 mm square or more is produced and then cooled.

The size of the seed single crystal can be appropriately selected according to the size of the ceramic sintered body.
It is preferable that the size is the same as that of the ceramic sintered body. It is sufficient that the thickness of this seed single crystal is at least 0.3 mm or more. At least one smooth surface preferably has a smoothness of about ± 1.0 μm, and is most preferably mirror-polished. .

In producing an oxide single crystal using the method of the present invention, first, as shown in FIG. 1 (a), a predetermined seed single crystal 1 and a ceramics sintered body 2 are prepared. All of these materials meet the above conditions,
At least one surface is smooth. Next, as shown in FIG. 1B, the smooth surface of the seed single crystal 1 and the smooth surface of the ceramic sintered body 2 are brought into contact with each other, and the weight 4 is placed on the ceramic sintered body 2. 1000 in a closed container 5 in a lead atmosphere
Heat at a temperature of ~ 1450 ° C. As the closed container 5 used here, a container made of at least one metal of platinum, palladium, rhodium and silver, or a dense porcelain pod is preferable. This is because the obtained single crystal is easily cracked with materials other than these. The weight 4 is
It can be appropriately selected depending on the shape of the sample, the manufacturing method, and the like. For example, when repeatedly used for a long time, it is preferable to use a platinum plate.

When the heating temperature is lower than 1000 ° C., the rate of single crystallization is extremely slow. On the other hand, when the heating temperature is higher than 1450 ° C., it becomes extremely difficult to prepare a large and uniform crystal. The time for heating the contacted ceramics sintered compact and the seed single crystal can be appropriately selected depending on the sample shape and the like. For example, when the thickness is 10 mm or less, it is preferably 10 to 500 hours. , And more preferably 100 to 2
By heating at the aforementioned temperature for 00 hours, FIG.
The single crystal 6 as shown in (c) is completed.

As described above, in the manufacturing method of the present invention, the specific ceramics sintered body and the seed single crystal are brought into contact with each other in a lead atmosphere in a closed container and heated,
Since the ceramics sintered body is made into a single crystal, it is possible to prevent cracks and foreign substances from being taken into the inside of the single crystal. Further, an oxide single crystal in which cracks do not occur in the oscillator even after polarization is obtained.

Moreover, by using the method of the present invention, a single crystal member having an arbitrary shape such as a triangular shape, a cylindrical shape, or a thin columnar shape can be manufactured. as a result,
It has become possible to stably provide an ultrasonic probe of any shape, which has higher sensitivity and higher reliability than the PZT-based piezoelectric ceramic.

The solid solution single crystal produced by the method of the present invention can be made into a single crystal having any orientation depending on the orientation of the seed crystal. For example, when the obtained single crystal is cut out perpendicularly to the [001] axis (or c axis), an electrode is formed on the (001) plane and polarization treatment is performed, excellent electromechanical coupling is obtained. A transducer with coefficients is obtained. Further, when the obtained single crystal is cut out perpendicularly to the [111] axis, an electrode is formed on the (111) plane, and polarization treatment is performed, a single crystal having a large dielectric constant is obtained. .

When the single crystal obtained by the method of the present invention is processed into a strip-shaped vibrator, the thickness direction ([00
1] axis) has a sound velocity of 2000 to 3500 m / s, and a frequency constant that is a product of a half-resonance frequency and a thickness is 1350 to 150.
0Hz ・ m, the frequency constant of PZT piezoelectric ceramic is 2
It becomes 000 to 3000 Hz · m and is delayed by about 25 to 50%. Further, the electromechanical coupling coefficient k ₃₃ is also excellent at 72 to 85% with little variation, and a large-sized and high-performance vibrator having a maximum diameter of about 100 mm can be obtained.

On the other hand, after the single crystal produced by the method of the present invention is cut in parallel with the [111] axis,
When the electrode is formed on the (111) plane, 2000 to 8
A vibrator having a high dielectric constant of about 000 can be obtained.

[0035]

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Example 1 In this example, Pb {(Mg _1/3 N
b _2/3 ) _0.68 Ti _0.32 } O ₃ was prepared as a solid solution single crystal (hereinafter abbreviated as PMNT 68/32).

First, the method for producing the seed single crystal used will be described in detail below. The seed single crystal is 80 mol% lead oxide (Pb
O) and 20% boron oxide (B ₂ O ₃ ) as a fluxing agent. As starting materials, chemically high-purity PbO, MgO, Nb ₂ O ₅ , and TiO
The powder of No. ₂ was used, these were mixed so as to have the composition shown in the above formula, and an equimolar amount of P was used as a flux.
It was added bO-B ₂ O ₃ flux. After thoroughly mixing this powder with a dry mixing machine, store it in a rubber container and
Rubber pressing was performed at a pressure of ton / cm ² . 600 g of the obtained lump was placed in a 250 cc platinum container with a diameter of 50 mm and dissolved by raising the temperature to 900 ° C. in 4 hours.

After cooling the obtained melt, a rubber-pressed lump containing the above-mentioned mixed powder and flux was further added to a 400 g platinum container, which was capped with platinum and fixed to the center of the electric furnace. . After heating up to 1200 ° C. in 12 hours, and then gradually cooling to 800 ° C. at a slowing rate of 1 ° C./hour,
It was allowed to cool to room temperature. During cooling, oxygen was selectively blown to one end of the lower part of the platinum crucible to cool the platinum crucible so that nucleation occurred at one place.

Then, the platinum crucible was boiled in 30% nitric acid for 8 hours to take out a single crystal, and the obtained single crystal was observed. As a result, the obtained single crystal had an arrowhead shape and the size was about 20 mm square.

When a part of the single crystal was crushed and subjected to X-ray diffraction to examine the crystal structure, it was confirmed that it had a perfect perovskite structure. Moreover, when the composition of this powder was analyzed by ICP, x was about 0.32. The lattice constant of this single crystal was 4.018 angstrom.

Furthermore, using a Laue camera, [001]
The direction of the axis was taken out and the sample was cut perpendicularly to this axis with a cutter to a thickness of 1 mm, and the obtained sample was mirror-polished. Next, this sample was cut into 12 mm squares to prepare 10 rectangular plate oscillators, which were used as seed crystals.

Next, the method for producing the ceramic sintered body will be described in detail. The ceramics sintered body was manufactured as follows using a usual solid-phase reaction method. First, using chemically high-purity PbO, MgO, Nb ₂ O ₅ and TiO ₂ powders as starting materials, Pb {(Mg _1/3 Nb
_2/3 ) _0.68 Ti _0.32 } O ₃ was prepared. Pure water was added to this mixed powder, and the mixture was crushed and dried in a nylon pot mill for 20 hours using a zirconia ball, and then calcined at 800 ° C. in an alumina sheath.

Next, 0.5 wt% of lead oxide was added to this calcined powder, pure water was added again, and the powder was pulverized by the above-mentioned pot mill and dried to obtain a powder. 5 wt% of a 5% PVA aqueous solution as a binder was added to this powder, mixed in a mortar, and passed through a 48 # sieve for granulation. The particles thus obtained were subjected to a pressure of 50 MPa in a mold to 40
It was temporarily molded into a column of mmφ × 15 mm.

Then, the temporary molded body is put into a rubber mold, and 100
It was molded with MPs using a hydrostatic press and degreased by heating in an electric oven at 500 ° C. for 4 hours. The molded body after degreasing is housed in a double high-density magnesia pod and baked at 1200 ° C. for 3 hours.
Hot pressing was performed in oxygen at a pressure of 20 MPa for 5 hours at 00 ° C. to obtain a sintered body.

When the density of the obtained sintered body was measured,
It was 99.5% of the theoretical density, and the crystal structure was a perfect single-phase perovskite structure. The lattice constant of this sintered body was 4.019 angstrom. A 12 mm × 12 mm × 5 mm rectangular plate was cut out from this hot pressed sintered body and one surface was mirror-polished to obtain a ceramic sintered body sample.

The difference between the lattice constant of the ceramic sintered body produced in this example and the lattice constant of the seed single crystal is
0.03%. Using the seed single crystal and the ceramics sintered body sample, an oxide single crystal was manufactured as follows.

First, the mirror surface of the seed single crystal and the mirror surface of the hot pressed sintered body are bonded together and placed in a platinum crucible, and several hot pressed sintered bodies of the same material are placed on top of the crucible. Placed. After sealing the platinum crucible,
These were further placed in a crucible made of magnesia, and heat-treated at 1280 ° C. for 170 hours in an electric furnace. After cooling, these were taken out and the fracture surface was observed. As a result, it was confirmed that no grain boundaries were seen and that they were single-crystallized.

From the newly single-crystallized portion of this heat-treated body, a 12 mm × 12 mm × 0.4 mm square plate was cut out and confirmed to be single-crystallized by the Laue x-ray method. Ten square plates having the same size were cut out, and Ni-Au electrodes were formed on both sides of each by using a sputtering method.
Furthermore, 1.5kV / m in 180 ° C silicone oil
An electric field of m was applied to carry out polarization treatment, and the device was cooled to room temperature as it was. As a result, cracking of the vibrator after polarization was not found in 10 out of 10.

The obtained vibrator was cut to a width of 150 μm with a diamond blade and the rectangular electromechanical coupling coefficient k ₃₃ ′ was measured. As a result, k ₃₃ ′ was 83%, and its variation was 2%. It was extremely small, within.

The oxide single crystal produced by the method of the present invention is particularly effective as a vibrator of an ultrasonic probe. An example of the ultrasonic probe is shown in FIG. In the ultrasonic probe 15 shown in FIG. 2, electrodes 9 and 10 are formed on the upper and lower surfaces of the single crystal material 7 manufactured by the method of the present invention. 8 is a backing material, 11 is an acoustic matching layer, 12 is an acoustic lens, 13 is a ground electrode, and 14 is a flexible printed board.

Such an ultrasonic probe has the same piezoelectric characteristics as described above and has high reliability. (Embodiment 2) In the present embodiment, Pb {(Sc _1/2 N
b _1/2 ) _0.29 (Mg _1/3 Nb _2/3 ) _0.34 Ti _0.37 } O ₃
Solid solution single crystal consisting of (hereinafter PSMNT 29/34 /
Abbreviated as 37. ) Manufactured.

First, the method for producing the seed single crystal used will be described in detail below. The seed single crystal is 75 mol% lead oxide PbO.
And a 25% boron oxide were used as a fluxing agent. As a starting material, chemically high purity (99.
9% or more) PbO, Sc ₂ O ₃ , MgO, Nb ₂ O ₅
And powders of TiO ₂ were used and prepared so as to have the composition shown by the above-mentioned formula, and a double molar amount of PbO—B ₂ O ₃ flux was added as a flux. After thoroughly mixing this powder with a dry mixing machine, it was housed in a rubber container and rubber-pressed at a pressure of 2 ton / cm ² . 600 g of the obtained lump was placed in a 250 cc platinum container with a diameter of 50 mm and dissolved by raising the temperature to 900 ° C. in 4 hours.

After cooling the obtained melt, a mass of the rubber-pressed mixture containing the above-mentioned mixed powder and flux was further added to a 400 g platinum container, which was capped with platinum and fixed to the center of the electric furnace. . After heating up to 1250 ° C. in 12 hours, and then gradually cooling to 800 ° C. at a slowing rate of 1 ° C./hour,
It was allowed to cool to room temperature. During cooling, nucleation was performed at one place by selectively blowing oxygen to a point below the platinum crucible to cool it.

Then, the platinum crucible was boiled with 30% nitric acid for 8 hours to take out a single crystal, and the obtained single crystal was observed. As a result, the obtained single crystal had an arrowhead shape and the size was about 20 mm square.

When a part of this single crystal was crushed and subjected to X-ray diffraction to examine the crystal structure, it was confirmed that it had a perfect perovskite structure. Further, chemical analysis of this powder was carried out by ICP, and it was confirmed that the composition value was almost the same as the charged value. The lattice constant of this single crystal was 4.025 angstrom.

Furthermore, using a Laue camera, [001]
The direction of the axis was taken out and the sample was cut perpendicularly to this axis with a cutter to a thickness of 1 mm, and the obtained sample was mirror-polished. Next, ten 12 mm square rectangular plate oscillators were produced from this sample, and this was used as a seed crystal.

Next, the method for producing the ceramic sintered body will be described in detail. The ceramics sintered body was manufactured as follows using a usual solid-phase reaction method. First, as a starting material, chemically high purity PbO, Sc ₂ O ₃ , MgO,
Using powders of Nb ₂ O ₅ and TiO ₂ , PSMN
T 29/34/37 and PSMNT 58/00 /
42 were prepared so as to have two kinds of compositions. Pure water was added to this mixed powder, and the mixture was crushed and dried in a nylon pot mill for 20 hours using a zirconia ball, and then this powder was calcined in an alumina sheath at 800 ° C.

Next, 0.5 wt% of lead oxide was added to the calcined powder, pure water was added again, and the powder was pulverized by the pot mill and dried to obtain a powder. To this powder, 5 wt% of a 5% PVA aqueous solution as a binder was added, mixed in a mortar, and passed through a 48 # sieve for granulation. The obtained particles are applied with a pressure of 50 MPa in a mold to 40 mmφ.
It was temporarily molded to x15 mm.

Then, the temporary molded body is put into a rubber mold, and 100
It was molded with MPs using a hydrostatic press and degreased by heating in an electric oven at 500 ° C. for 4 hours. The molded body after degreasing was housed in a double high-density magnesia pod and baked at 1250 ° C. for 3 hours.
Hot pressing was performed in oxygen at a pressure of 20 MPa for 5 hours at 00 ° C. to obtain a sintered body.

When the density of the obtained sintered body was measured,
The theoretical density was 99.7%, and the crystal structure was a perfect perovskite structure. The sintered body has a lattice constant of 4.025 Å for PSMNT 29/34/37, and a lattice constant of 4.25 for PSMNT 58/00/42.
It was 030 angstroms. A 12 mm × 12 mm × 5 mm rectangular plate was cut out from this hot pressed sintered body and one surface was mirror-polished to obtain a ceramic sintered body sample.

The difference between the lattice constant of the ceramic sintered body produced in this example and the lattice constant of the seed single crystal is P
Almost no SMNT 29/34/37, but PSM
It is 0.15% in NT58 / 00/42. Using the seed single crystal and the ceramics sintered body sample, an oxide single crystal was manufactured as follows.

First, the mirror surface of the above-mentioned seed single crystal and the mirror surface of the hot-press sintered body were stuck together and put in a platinum crucible, and several hot-press sintered bodies were placed as a weight on the upper part thereof. . After sealing the platinum crucible, put them in a magnesia crucible and put them in an electric furnace for 1280
Heat treatment was performed at 170 ° C. for 170 hours. After cooling, taking out these and observing the fracture surface, no grain boundary was observed,
It was confirmed that it had become a single crystal.

A 12 mm × 12 mm × 0.4 mm square plate was cut out from the newly single-crystallized portion of this heat-treated body, and it was confirmed by the Laue x-ray method that it was single-crystallized. Ten square plates having the same size were cut out, and Ni-Au electrodes were formed on both sides of each by using a sputtering method.
Furthermore, an electric field of 2 kV / mm was applied in silicon oil at 220 ° C. to perform polarization treatment, and the product was cooled to room temperature as it was. As a result, cracking of the vibrator after polarization was not found in 10 out of 10.

The vibrator thus obtained was cut to a width of 150 μm using a diamond blade, and the electromechanical coupling coefficient k ₃₃
As a result of measuring ′, k ₃₃ ′ was 80%, and the variation was extremely small within 2%.

(Embodiment 3) In the present embodiment, Pb
{(Zn _1/3 Nb _2/3 ) _0.30 (Mg _1/3 Nb _2/3 ) _0.23
(Sc _1/2 Ta _1/2 ) _0.18 Ti _0.29 } O ₃ solid solution single crystal (hereinafter PZMNSTT 30/23/18/2
(Abbreviated as 9) was produced.

First, the method for producing the seed single crystal used will be described in detail below. Seed single crystal is 90 mol% lead oxide Pb
It was prepared by a flux method using O and 10% boron oxide as a flux. As a starting material, chemically pure P
Powders of bO, Sc ₂ O ₃ , MgO, Nb ₂ O ₅ , Ta ₂ O ₅ and TiO ₂ were used, and these were compounded so as to have the composition shown by the above-mentioned formula, and further used as a flux.
Twice the molar amount of PbO-B ₂ O ₃ flux is added to the mixed powder. The obtained powder was subjected to rubber pressing in the same manner as described above and then dissolved.

After cooling this, it was fixed to the center of the electric furnace in the same manner as described above. The temperature was raised to 1250 ° C. in 12 hours, then gradually cooled to 800 ° C. at a slow cooling rate of 1 ° C./hour, and further allowed to cool to room temperature. During cooling, oxygen was selectively blown to one point on the lower part of the platinum crucible to cool it so that nucleation occurred at one place.

Then, the platinum crucible was boiled with 30% nitric acid for 8 hours to take out a single crystal, and the obtained single crystal was observed. As a result, the obtained single crystal had an arrowhead shape and the size was about 20 mm square.

A part of this single crystal was crushed and subjected to X-ray diffraction to examine the crystal structure. As a result, it was confirmed that the single crystal had a perfect perovskite structure. When the composition of this powder was analyzed by ICP, it was found that the composition values were almost the same as the charged values. The lattice constant of this single crystal is 4.
It was 034 angstroms.

Furthermore, using a Laue camera, [001]
The azimuth of the axis was taken out, and the sample obtained by cutting with a cutter perpendicularly to this axis to a thickness of 1 mm was mirror-polished. Next, this sample was cut into 12 mm squares to prepare 10 rectangular plate oscillators, which were used as seed crystals.

The ceramic sintered body is used as a starting material.
Chemically high purity PbO, Sc ₂ O ₃ , MgO, Nb ₂
Powders of O ₅ , Ta ₂ O ₅ and TiO ₂ are used, Pb
{(Zn _1/3 Nb _2/3 ) _0.30 (Mg _1/3 Nb _2/3 ) _0.23
(Sc _1/2 Ta _1/2 ) _0.18 Ti _0.29 } O ₃ was prepared. Pure water was added to the mixed powder, and zirconia balls were used for 20 hours in a nylon pot mill.
Mix, crush and dry, then 80 in alumina pod
It was calcined at 0 ° C.

Next, 0.5 wt% of lead oxide was added to this calcined powder, pure water was added again, and the powder was pulverized by the above-mentioned pot mill and dried to obtain a powder. 5 wt% of a 5% PVA aqueous solution as a binder was added to this powder, mixed in a mortar, and passed through a 48 # sieve for granulation. The particles thus obtained were subjected to a pressure of 50 MPa in a mold to 40
It was temporarily molded into mmφ × 15 mm.

Then, the temporary molded body is put into a rubber mold, and 100
It was molded with MPs using a hydrostatic press and degreased by heating in an electric oven at 500 ° C. for 4 hours. The degreased molded body was housed in a double high-density magnesia sheath and baked at 1300 ° C. for 4 hours.
Hot pressing was performed in oxygen at 50 ° C. for 5 hours to obtain a sintered body.

When the density of the obtained sintered body was measured,
The theoretical density was 99.2%, the crystal structure was a single layer perovskite structure, and the lattice constant of this sintered body was 4.034 angstrom. A 12 mm × 12 mm × 5 mm rectangular plate was cut out from this hot press sintered body and one surface was mirror-polished to obtain a ceramic sintered body sample.

A single crystal plate of SrTiO ₃ mirror-polished in the (110) direction was prepared. This lattice constant is 3.
903 angstroms. Using this as a substrate, the above-mentioned 30PZN-23PMN-18PST-2 is placed on top of it.
9PT was placed.

The difference between the lattice constant of the ceramic sintered body produced in this example and the lattice constant of the seed single crystal is
It is 3.3%. Using the seed single crystal and the ceramics sintered body sample, an oxide single crystal was manufactured as follows.

First, the mirror surface of the above-mentioned seed single crystal and the mirror surface of the hot pressed sintered body were stuck together and placed in a platinum crucible, and several hot pressed sintered bodies were placed as weights on the crucible. . After sealing the platinum crucible, put them in a magnesia crucible and put them in an electric furnace for 1280
Heat treatment was performed at 170 ° C. for 170 hours. After cooling, taking out these and observing the fracture surface, no grain boundaries were seen,
It was confirmed that it had become a single crystal.

From the newly single-crystallized portion of this heat-treated body, a 12 mm × 12 mm × 0.4 mm square plate was cut out and confirmed to be single-crystallized by the Laue x-ray method. Ten square plates having the same size were cut out, and Ni-Au electrodes were formed on both sides of each by using a sputtering method.
Furthermore, an electric field of 2 kV / mm was applied in silicon oil at 220 ° C. to perform polarization treatment, and the product was cooled to room temperature as it was. As a result, cracking of the vibrator after polarization was not found in 10 out of 10.

The obtained vibrator was cut to a width of 150 μm with a diamond blade and the rectangular electromechanical coupling coefficient k ₃₃ ′ was measured. As a result, k ₃₃ ′ was 81%, and its variation was 2. It was extremely small, within 5%.

As described above, in Examples 1 and 2, a single crystal was manufactured by the method of the present invention using the ceramics sintered body having the same composition and the seed single crystal. In Example 3, SrTiO ₃ having a perovskite structure was manufactured. Was used as a seed crystal, but the present invention is not limited to this.

An MgO single crystal having a lattice constant of 4.20 Å was used as a seed crystal, and Pb (Mg) having a lattice constant of 4.041 Å was used as a ceramic material.
_{When 1/3} Nb _2/3 ) O ₃ was used to perform heat treatment in a closed container in the same manner as described above, single crystallization was similarly confirmed.

As a seed crystal, TiO ₂ A plane (4.5
9 angstroms) and PMN (4.04 angstroms) or PSN (4.0 angstroms) in the same manner as described above.
8 angstroms), the oxide obtained after heating was polycrystalline and further cracked. In this case, the difference between the lattice constant of the seed single crystal and the lattice constant of the ceramic sintered body was 13.6%, respectively.
And 11.1%. That is, the difference in lattice constant is 1
It is understood that when a seed single crystal exceeding 0% and a ceramics sintered body are used, not only a single crystal oxide cannot be obtained, but also cracks occur.

From the above results, it was found that by using the manufacturing method of the present invention, a single crystal having a large size with few cracks and foreign substances and having stable characteristics after polarization can be obtained.

In the above embodiment, (PMNT68
/ 32), (PSMNT 29/34/37) and (PZMNSTT 30/23/18/29) as examples, the production method of the present invention has been described, but the present invention is not limited thereto. . Pb {(Sc _1/2 Nb _1/2 ) _0.58 Ti _0.42 } O, which is another similar piezoelectric single crystal material
₃ or Pb {(Sc _1/2 Ta _1/2 ) _0.55 Ti _0.37 } O ₃ or Pb {(Yb _1/2 Nb _1/2 ) _0.50 } O ₃ , Pb {(In
Similar results are obtained when _1/2 Nb _1/2 ) _0.63 Ti _0.37 } O ₃ is included.

[0084]

As described in detail above, according to the present invention,
It is possible to obtain a method capable of producing a large single crystal exhibiting stable characteristics even after polarization with few cracks and foreign substances. The single crystal manufactured by the method of the present invention is particularly effective as a vibrator of an ultrasonic probe, but in addition to this, non-destructive inspection equipment, capacitor materials or optical materials, etc., all of which single crystal materials are used. Is expected to be effective for

[Brief description of the drawings]

FIG. 1 is a diagram showing the concept of a method for producing an oxide single crystal of the present invention.

FIG. 2 is a perspective view showing the configuration of a strip-shaped oscillator of a probe using a single crystal manufactured by the method of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Seed single crystal, 2 ... Ceramics sintered body, 3 ... Closed container, 4 ... Weight 5 ... Closed container, 6 ... Completed single crystal, 7 ... Single crystal material,
8 ... Backing material 9 ... Electrode, 10 ... Electrode, 11 ... Acoustic matching layer, 12
… Acoustic lens 13… Earth electrode, 14… Flexible printed board, 1
5 ... Ultrasonic probe.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Shiro Saito 1 Toshiba R & D Center, Komukai Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa

Claims (3)

[Claims] 1. A smooth surface of a ceramic sintered body, which is represented by the following general formula (1), is composed of a composite perovskite compound having a sintered density of 99% or more of a theoretical density, and has at least one smooth surface: A step of contacting with a smooth surface of a seed single crystal having a lattice constant within ± 10% of the lattice constant of this ceramic sintered body and having at least one surface being smooth, and the smooth surfaces being brought into contact with each other. The ceramics sintered body and the seed single crystal were placed in a sealed container in a lead atmosphere at 1000 to 14
And a step of heating at a temperature of 50 ° C. for producing an oxide single crystal. Pb {(B ¹ , B ² ) _1-x Ti _x } O ₃ General formula (1) (In the general formula (1), x is a value of 0 or more and 0.55 or less, and B ¹ is Zn, Mg. , Ni, Sc, Yb and In
B ² is Nb or Ta. ) 2. The composite perovskite compound is ABO
When expressed as ₃ , the ratio of A site and B site (A / B)
Is 1.00 or more and 1.10 or less, The manufacturing method of the oxide single crystal of Claim 1. (A is Pb and B is {(B
¹ , B ² ) _1-x Ti _x }. ) 3. The method for producing an oxide single crystal according to claim 1, wherein the composition system of the seed single crystal is the same as the composition system of the perovskite compound.