CN1196817C - Growth of lead indium niobate-lead titanate single crystal with high Curie point by crucible descent method - Google Patents

Abstract

The present invention relates to a Bridgman method for the growth of lead indium niobate-lead titanate single crystal (PINT), which belongs to the field of crystal growth. The present invention is characterized in that the composition of crystals is xPIN-(1-x)PT, wherein PIN represents Pb(In-(1/2)Nb-(1/2))O3, PT represents PbTiO3, and x=0.50 to 0.70. The range of furnace temperature for crystal growth is from 1350 to 1430 DEG C, the descending speed rate of a crucible is from 0.1 to 2.0 mm/h, and the maximal temperature gradient is not smaller than 50 DEG C /cm; PMNT single crystals of heterogeneous isomorphism are used as seed crystals, S(seed crystals)/S(crystals) is larger than or equal to 70%; a closed platinum crucible is selected to be used as a growth crucible. PINT single crystals with the diameter larger than 40mm and the length larger than 60mm can be produced by the technology of the present invention, and the piezoelectric property can reach d33 larger than 2000 pC/N and k33 larger than 90%. The requirements of high technology application of ultrasonic imaging, high-strain drivers, etc. to the properties of crystal materials can be satisfied, and the requirements of high technology application of ultrasonic imaging, high-strain drivers, etc. to the use temperature of crystal materials can be satisfied.

Description

Growth of lead indium niobate-lead titanate single crystal with high Curie point by crucible descent method

Technical field

The invention relates to a method for preparing high Curie point relaxation ferroelectric single crystal lead indium niobate-lead titanate (PINT) with heterogeneous isomorphic lead magnesium niobate-lead titanate seed crystals, more precisely relates to The temperature gradient method, especially the crucible descent method, grows (prepares) the relaxation ferroelectric single crystal PINT. The chemical composition of the crystal can be expressed as xPb(In _1/2 Nb _1/2 )O ₃ -(1-x)PbTiO ₃ , abbreviated as PINT, or PIN-PT. It belongs to the field of crystal growth.

Background technique

Lead magnesium niobate-lead titanate (PMNT) and lead zincate-lead titanate (PZNT) single crystals with quasi-isomorphic phase boundary composition have very high piezoelectric constants, which are comparable to the commonly used piezoelectric materials PZT ferroelectric ceramics. Ratio, its piezoelectric constant d ₃₃ and electromechanical coupling coefficient k ₃₃ have increased from about 600pC/N and 70% to 2000pC/N and over 90% respectively, and its strain is as high as 1%, which is about 0.1% higher than the usual strain Piezoelectric materials are an order of magnitude higher. The superior piezoelectric and electromechanical coupling properties of relaxor ferroelectric single crystal materials make it have broad application prospects in electroacoustic conversion such as medical ultrasonic imaging, sonar, and industrial non-destructive flaw detection. The new generation of B-scan ultrasonic imager (B-ultrasound) using it as a probe will greatly improve its image resolution and frequency bandwidth; however, due to the low Curie temperature of PMNT and PZNT of quasi-isomorphic phase boundary components, they are 150°C respectively and 170°C. Therefore, its temperature stability during use is poor, that is, it is easy to age. Its operating temperature generally cannot exceed 85°C, which is far lower than the operating temperature of PZT ceramics.

PINT ceramics have a high Curie temperature (>250°C), and the relaxation ferroelectric PINT single crystal is grown by flux method [N.Yasuda, H.Ohwa, M.Kume and Y.Yamsshita: Jpn.J. Appl.Phys.39(2000)L68], although its composition deviates far from the original quasi-isotype phase boundary composition. However, the research results found that the crystal has good piezoelectric properties and high temperature stability. However, the growth of relaxor ferroelectric single crystal by flux method has its inherent disadvantages, mainly in that when the crystal grows at high temperature, the highly toxic PbO is easy to volatilize, which not only requires strict protection facilities for growth, but also causes the growth solution to The degree of supersaturation changes greatly, and it is difficult to control the nucleation of crystals; due to the different volatilization of each component of the raw material, it is easy to form component segregation, which makes the integrity of the growing crystal poor; due to the limitation of solubility, the size of the grown crystal is small, It cannot meet the application requirements of ultrasonic imaging and high-strain drivers, and the production efficiency is low, and large-scale production cannot be realized. Since the composition of the relaxor ferroelectric single crystal is relatively complex, it is easy to deviate from the stoichiometry during growth, and it is easy to form a pyrochlore phase, so its growth is relatively difficult.

So far, there is no publication disclosing a preparation method for growing PINT crystals by the crucible drop method.

Contents of the invention

The object of the present invention is to provide a method of growing lead indium niobate-lead titanate single crystal by using a heterogeneous isomorphic seed crystal as a seed crystal and using a crucible drop method. That is, the heterogeneous isomorphic seed crystal with stable perovskite phase-lead magnesium niobate-lead titanate seed crystal is used to grow a relaxor ferroelectric single crystal with poor perovskite phase stability.

The object of the present invention is to realize by a kind of crucible descending method growth PINT single crystal, comprising:

(1) Raw material handling

Regarding raw material processing, it is mainly to determine the x value according to the xPIN-(1-x)PT chemical formula and then accurately weigh various oxide raw materials.

The raw material processing includes batching, mixing, and calcination. The purity of the raw materials is generally required to be above 3N, preferably above 4N, preferably mixed on a ball mill. First, In ₂ O ₃ and Nb ₂ O ₅ with a purity greater than 99.99% are pre-synthesized into InNbO ₄ at 1000-1300°C, and then PbO, InNbO ₄ , and TiO ₂ powders are mixed according to the xPIN-(1-x)PT chemical formula Raw materials, x = 0.50-0.70; then the prepared raw materials are ball-milled for 1-10 hours and mixed into a uniform powder, and then the powder is pre-fired at 700-1000° C. for 1-3 hours. as a starting material for crystal growth.

(2) Selection of crucible

There are also no strict restrictions on the crucible, as long as it can withstand the growth temperature and does not react with the raw material, such as metal or alloy crucibles, especially precious metal crucibles, such as platinum crucibles, iridium crucibles. Among them, simple platinum crucibles are preferred. In order to prevent the volatilization of PbO and the sublimation of In ₂ O ₃ , the platinum crucible filled with seed crystal and growth raw material was properly sealed for crystal growth.

The thickness and shape of the crucible are not strictly limited, and the thinner the better under the premise of being able to withstand the melt, so as to reduce the cost as much as possible. The number and shape of crucibles are also not strictly limited. In order to reduce costs, it is preferable to have multiple crucibles in one furnace, especially special-shaped crucibles, that is, special-shaped crucibles with crystal shapes required by users. In this regard, a number of patents of Shanghai Institute of Ceramics, Chinese Academy of Sciences have been published, such as CN1113970A, the content of which is incorporated by reference in the present invention. The diameter of the platinum crucible in the present invention can be large or small, generally 10-50mm, and the length of the crucible is not limited, generally 200-400mm, and the platinum crucible can be made into a corresponding shape according to the shape of the required PINT crystal , and the platinum crucible can be a sealed single-layer or double-layer or even triple-layer structure (the thickness of each layer is preferably 0.10-0.20mm), so as to prevent the corrosion and volatilization of PbO.

(3) Growth process selection

The difficulty of growing PINT by the crucible drop method is to determine the appropriate growth process conditions, including determining the temperature field distribution of the growth furnace, the temperature gradient, the speed of the crucible drop, the determination of the inoculation position, and the temperature field in the furnace as the crucible drops. Adjust to avoid the generation of pyrochlore phase and ensure the growth of PINT single crystal with uniform composition.

When growing PINT single crystal, due to the poor stability of PINT perovskite, it is better to use PMNT single crystal with no body defects as the seed crystal, that is, lead magnesium niobate-lead titanate single crystal as the seed crystal. , the specific molecular formula is xPb(Mg _1/3 Nb _2/3 )O ₃ -(1-x)PbTiO ₃ , x=0.60～0.76. The direction of the seed crystal is not strictly limited and can be determined according to user needs. It is generally <111> or <110>, and the crystallographic direction of the PINT single crystal can be determined at room temperature with a commercially available single crystal X-ray diffractometer as the seed crystal direction. The shape of the seed crystal is not limited, and the shape of the crucible is not particularly required, and it can be a cylinder, a square prism or other polyhedrons. Also not limited to the size of the seed, depending on the size of the crucible, it is generally preferred that the ratio of the cross-sectional area of the seed (S-seed) to the cross-sectional area of the grown crystal (S- _crystal ) (S _-seed /S- _crystal ) be greater than 70%.

The furnace temperature is 1350-1430°C, and the maximum temperature gradient in the descending direction of the crucible is not less than 50°C/cm, so as to ensure that the raw materials are fully melted in the crucible and the components are uniformly diffused. Melt the crucible at the inoculation position and keep it warm for 3 to 10 hours, then start to grow. Generally, the crucible is lowered at a speed of 0.1 to 2 mm/hr, and a complete PINT single crystal with the same direction as the seed crystal and the same shape as the crucible can be grown. . The descending speed of the crucible depends on the shape and size of the crucible, the quantity of the crucible, the amount of raw materials, the temperature gradient and the heat preservation conditions in the device, etc., which are well known to those skilled in the art.

There are no strict restrictions on the growth equipment, and general temperature gradient method devices can be used. In this regard, multiple patents of Shanghai Institute of Ceramics have been disclosed, such as CN1113970A, the content of which is incorporated by reference in the present invention.

In summary, the present invention is characterized in that:

(1) The crystal composition is x PIN-(1-x)PT, wherein PIN represents Pb(In _1/2 Nb _1/2 )O ₃ , PT represents PbTiO ₃ , and x=0.50-0.70.

(2) The temperature range of the crystal growth furnace is 1350-1430°C, the rate of crucible descent is 0.1-2.0mm/h, and the maximum temperature gradient is not less than 50°C/cm.

(3) S _{seed crystal} /S _crystal ≥ 70% during crystal growth, generally 70-85%, the crucible is at the inoculation position to melt the raw material and keep it warm for 3-10 hours to start growing.

(4) Generally, a sealed platinum crucible is used as the growth crucible. The shape of the crucible can be varied. Generally, it is a special-shaped crucible according to the crystal shape required by the user. It can be a sealed single-layer, double-layer or even three-layer structure. The thickness of each layer 0.10-0.20mm.

The piezoelectric coefficient d of the PINT single crystal involved in the present invention is directly measured with the ZJ-3A type d ₃₃ tester manufactured by the Institute of Acoustics, Chinese Academy of Sciences; _the dielectric constant is converted after measuring the sample capacitance with the HP4192A type impedance analyzer Obtained; the measurement of the electromechanical coupling coefficient k ₃₃ is based on the IEEE176-78 standard, after measuring the resistance R or conductance G at different frequencies with the HP4192A impedance analyzer, it is calculated according to the well-known formula. The hysteresis loop is tested with a modified Sawyer-Tower system in an electric field at a frequency of 20 Hz. The strain curve is tested with a linear variable integral transducer (LVDT).

The present invention compares with the method for growing PINT single crystal with flux, and its advantage is, 1. owing to have utilized the PMNT single crystal of heterogeneous isomorphism as the seed crystal of growth, therefore can preferably suppress the pyrochlore phase in the crystal growth process The formation of crystals is better [Fig. 2]. 2. Since the growth material is sealed in the platinum crucible, PbO will not volatilize and cause no environmental pollution. 3. Since the platinum crucible containing the seed crystal and the growth raw material is properly sealed for crystal growth, the composition of the grown PINT crystal deviates less from its original chemical composition, and the piezoelectric performance of the crystal is good. 4. The crystal growth equipment is simple, the growth process parameters are easy to control, and the uniformity, repeatability, and consistency of the grown PINT crystal are relatively good. 5. Since multiple crucibles can grow crystals at the same time, the production efficiency is high, and it is suitable for large-scale production of PINT crystals with a diameter greater than 40mm and a length greater than 60mm.

The technique of the invention can grow PINT single crystal with piezoelectric constant _d33 greater than 2000pC/N and electromechanical coupling coefficient _k33 of 94%. The method of the invention can solve the growth problem of the relaxation ferroelectric single crystal PINT with poor perovskite phase stability, and realize the large-scale industrial production of the PINT single crystal. It can be seen from this that we have invented a method for growing a relaxor ferroelectric single crystal with a stable perovskite phase using a heterogeneous isomorphic seed crystal with a stable perovskite phase, which can prepare a high Curie point, superior The PINT single crystal with piezoelectric properties is of great significance for improving the operating temperature of high-strain drivers and obtaining medical B-ultrasound.

Description of drawings

Fig. 1 is the crystal growth furnace used in the present invention, wherein 1 is a heating device, 2 is a platinum crucible, 3 is a filling material, and 4 is a down-leading device.

Fig. 2 is the PINT single crystal grown by the preparation method provided by the present invention.

Figure 3 is the X-ray diffraction pattern of the crystal, which shows that the grown crystal has a pure perovskite structure.

Figure 4 shows the variation of the electromechanical coupling coefficient k ₃₃ of longitudinal stretching vibration of 0.66PIN-0.34PT single crystal with temperature. The abscissa is the temperature (°C), and the ordinate is the electromechanical coupling coefficient k ₃₃ .

Figures 5-7 show the relationship between the dielectric constant (ε), loss factor (tanδ) and temperature (T) of <001>, <110>, <111> orientation 0.66PIN-0.34PT single crystal, respectively. The abscissa is temperature (°C), the ordinate on the left represents the dielectric constant, and the ordinate on the right represents the dielectric loss factor (%). The test frequencies shown in the figure are 100Hz, 1kHz and 10kHz respectively, the dotted line is the fresh sample, and the solid line is the polarized sample.

Figures 8-10 are the hysteresis loops of <001>, <110>, <111> orientation 0.66PIN-0.34PT single crystals respectively. The abscissa represents the electric field intensity (kV/cm), and the ordinate represents the polarization intensity (μc/cm ² ).

Figures 11-13 are the strain curves of <001>, <110>, <111> orientation 0.66PIN-0.34PT single crystals respectively. The applied electric field is a bidirectional electric field, and the maximum electric field strength is 20kV/cm. The abscissa represents the electric field strength (kV/cm), and the ordinate represents the strain (%).

Figure 14 shows the relationship between the dielectric constant (ε), loss factor (tanδ) and temperature (T) of the polarized sample of <001> orientation 0.60PIN-0.40PT single crystal. The abscissa is temperature (°C), the ordinate on the left represents the dielectric constant, and the ordinate on the right represents the dielectric loss factor (%). The test frequencies shown in the figure are 100Hz, 1kHz and 10kHz respectively.

Detailed ways

In order to further understand the substantive features and remarkable progress of the present invention, the present invention will be further described below in conjunction with the embodiments with reference to the accompanying drawings. It is obvious that the embodiments are only for the purpose of illustration, and in no way limit the present invention.

Example 1.

In ₂ O ₃ and Nb ₂ O ₅ with a purity greater than 99.99% were pre-synthesized into InNbO ₄ at 1150°C, and then PbO, InNbO ₄ , and TiO ₂ powders were formulated into mixed powders at a ratio of 0.66PIN-0.34PT. Mixed by ball milling for 10 hours to form a uniform powder, and then pre-calcined the powder at 850° C. for 2 hours. as a starting material for crystal growth. Then the powder was put into a cylindrical platinum crucible with a diameter of 20 mm for crystal growth. In the single crystal descending furnace, the maximum temperature gradient along the descending direction of the crucible is 70°C/cm, and PMNT seed crystals are used for growth. The powder was melted at a temperature of 1350°C, and after 4 hours of heat preservation, the crucible was lowered at a speed of 0.6mm/hr, and PINT crystals with a tripartite structure were grown. The dielectric, hysteresis loops, and electric field-induced strains of the three orientations of the grown PINT crystal are shown in Figure 5-13. The piezoelectric constant d ₃₃ of the single crystal is about 2000pC/N measured with a quasi-static d ₃₃ measuring instrument. The electromechanical coupling coefficient k ₃₃ of the PINT single crystal measured by the resonance anti-resonance method is 94%, see Figure 4.

Example 2

In ₂ O ₃ and Nb ₂ O ₅ with a purity greater than 99.99% were pre-synthesized into InNbO ₄ at 1100°C, and then PbO, InNbO ₄ , and TiO ₂ powders were formulated into mixed powders at a ratio of 0.60PIN-0.40PT. Mixed by ball milling for 8 hours to form a uniform powder, and then the powder was pre-calcined at 700°C for 3 hours. as a starting material for crystal growth. Put high-purity 99.99% PbO, In ₂ O ₃ , Nb ₂ O ₅ , TiO ₂ and Pb ₃ O ₄ powders into a cylindrical platinum crucible with a diameter of 20 mm for crystal growth, S Seed/S crystal = 70%. In the single crystal descending furnace, the maximum temperature gradient along the descending direction of the crucible is 70°C/cm, and heterogeneous and isomorphic PMNT seed crystals are used for growth, and the ratio is 71/29. The powder was melted at a temperature of 1350°C, and after 4 hours of heat preservation, the crucible was lowered at a speed of 0.2mm/hr, and PINT crystals with a tetragonal phase structure were grown. Its dielectric curve is shown in Figure 14.

Example 3.

High-purity 99.99% PbO, In ₂ O ₃ , Nb ₂ O ₅ , and TiO ₂ powders are prepared into 0.66PIN-0.34PT mixed powders as starting materials for crystal growth. Put 4 cylindrical platinum crucibles with a diameter of 40 mm in the single crystal drop furnace, and grow PINT crystals with the ratio of cross-sectional area S _{seed crystal} /S _crystal to 70%, and the crystallization direction of the seed crystal is <111>. After raising the temperature to 1380° C. and maintaining the temperature for 10 hours, crystal growth was carried out at a crucible descending speed of 1.0 mm/hr.

Claims (6)

1, a kind of falling crucible method of the high curie point lead niobate lead indate-lead-lead titanate monocrystal of growing comprises: raw material is handled, the fusing that heats up, and crucible degrowth, cooling crystal growing process is characterized in that:

(1) crystal consists of x PIN-(1-x) PT, and wherein PIN represents Pb (In _1/2Nb _1/2) O ₃, PT represents PbTiO ₃, x=0.50-0.70;

(2) 1350-1430 ℃ of crystal growth furnace temperature scope, the speed that crucible descends is 0.1-2.0mm/h, maximum temperature gradient is 70 ℃/cm;

(3) make seed crystal, S with the PMNT monocrystalline of heterogeneous isomorphism _{Seed crystal}/ S _Crystal=70%;

(4) select for use the platinum crucible of sealing as growth crucible.

2, by the falling crucible method of the described growth high curie point of claim 1 lead niobate lead indate-lead-lead titanate monocrystal, it is characterized in that described PMNT monocrystalline as seed crystal, concrete molecular formula is xPb (Mg _1/3Nb _2/3) O ₃-(1-x) PbTiO ₃, x=0.60～0.70.

3, by the falling crucible method of the described growth high curie point of claim 2 lead niobate lead indate-lead-lead titanate monocrystal, it is characterized in that being＜111 as the PMNT single-crystal orientation of seed crystal or＜110.

4,, it is characterized in that at first purity greater than 99.99% In by the falling crucible method of the described growth high curie point of claim 1 lead niobate lead indate-lead-lead titanate monocrystal ₂O ₃And Nb ₂O ₅At 1000-1300 ℃ of pre-synthetic InNbO ₄, then with PbO, InNbO ₄, TiO ₂Be made into compound by xPIN-(1-x) PT chemical formula, behind 1～10 hour uniform mixing of ball milling,, expect as rising of crystal growth again at 700-1000 ℃ of pre-burning 1-3 hour.

5,, it is characterized in that after the inoculation position makes the raw material fusing and is incubated 3～10 hours, beginning degrowth at crucible by the falling crucible method of the described growth high curie point of claim 1 lead niobate lead indate-lead-lead titanate monocrystal.

6, by the falling crucible method of the described growth high curie point of claim 1 lead niobate lead indate-lead-lead titanate monocrystal, it is characterized in that described crucible shape is varied, or individual layer or the multilayer or the three-decker of sealing, every layer thickness 0.10-0.20mm.

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