A material rod for the growth of relaxor ferroelectric single crystal and its preparation method, and material rod manufacturing device

Abstract

The present invention relates to a material rod for the growth of relaxor ferroelectric single crystals and a preparation method and a material rod manufacturing device. The method comprises the following steps: step 1): preparing raw materials according to the stoichiometric ratio of relaxor ferroelectric single crystal materials, placing the raw materials in a raw material melting zone of a container, heating the raw material melting zone to melt the raw materials and keep them warm; step 2): then heating a casting control zone of the container, the casting control zone is connected to the raw material melting zone, so that the molten raw material remains in a molten state, flows into a mold through the casting control zone, and obtains a material rod for the growth of relaxor ferroelectric single crystals after cooling; optionally, when the raw materials are melted and kept warm in step 1) and when the molten raw materials are flowed into the mold through the casting control zone in step 2), oxygen is introduced into the raw material melting zone.

Description

Technical Field

[0001] The invention belongs to the field of piezoelectric crystal materials, and in particular relates to a material rod for growing a relaxor ferroelectric single crystal, a preparation method thereof, and a material rod manufacturing device. Background Art

[0002] The research on relaxor ferroelectric single crystal materials began in the 1990s and has been a hot topic in the field of ferroelectric and piezoelectric materials research at home and abroad for many years. Relaxor ferroelectric single crystal materials have very excellent piezoelectric properties, such as their piezoelectric constant d 33 Reaching over 1500pC / N, 4-5 times higher than PZT, the electro-strain reaches 1.7%, an order of magnitude higher than PZT ceramics, and the electromechanical coupling factor k 33 Reaching over 90%, significantly higher than the electromechanical coupling factor of PZT which is about 70%. In March 1997, Science magazine published a special article reviewing the new relaxor ferroelectric crystal material, which was considered to be an exciting revolution in the field of ferroelectric materials in the past half century. In January 2000, the British magazine Nature reported in detail the research progress in the growth, preparation, performance and application of relaxor ferroelectric crystal materials. In recent years, the United States, Japan, South Korea and other countries have carried out large-scale research on relaxor ferroelectric single crystal materials and devices.

[0003] The application of relaxor ferroelectric single crystal materials in transducers is expected to greatly improve the sensitivity and power of transducers, reduce their volume and weight, and find important applications in broadband, high-sensitivity, miniaturized transducers and arrays, thereby promoting the leapfrog development of my country's medical ultrasound imaging systems and underwater acoustic equipment.

[0004] Relaxor ferroelectric single crystals are a large class of crystalline materials, which are characterized by having an ABO3 composite perovskite structure. The A-site ion is generally Pb 2+ , B-site ion is Zn 2+ Mg 2+ ,Sc 2+ ,In 3+ ,Nb 5+ ,Ti 4+ Therefore, lead zinc niobate-lead titanate [Pb(Zn 1 / 3 Nb 2 / 3 )O3-PbTiO3 (abbreviated as PZN-PT or PZNT)], lead magnesium niobate-lead titanate [Pb(Mg 1 / 3 Nb 2 / 3)O3-PbTiO3 (abbreviated as PMN-PT or PMNT)] all belong to relaxor ferroelectric single crystals. Depending on the B-site ions, there are other binary, ternary and quaternary systems. Generally speaking, relaxor ferroelectric single crystals are mostly solid solution crystals, and they all have a common component PbTiO3. They can have very excellent piezoelectric properties near the quasi-modular phase boundary (MPB) of the solid solution. Relaxor ferroelectric single crystals with different components have differences in the thermodynamic stability, melting temperature, growth habit, phase transition temperature and other aspects of the perovskite phase. For example, the thermodynamic stability of the perovskite phase of the PZN-PT single crystal is poor, and it is a non-uniform melting crystal. It cannot be grown by the melt method. It is generally grown by the flux method. The growth controllability is poor, and the crystal is difficult to grow. The thermodynamic stability of the perovskite phase of the PMN-PT single crystal is better. It is a uniform melting crystal and can be grown by the melt method. The growth controllability is good and the crystal is easy to grow. In terms of phase transition temperature, the Curie temperature of PZN-PT with better piezoelectric performance can be 150-170℃, and the Curie temperature of PMN-PT with better piezoelectric performance can be 135-145℃.

[0005] After twenty years of development, three generations of piezoelectric single crystals have been formed. The first generation of relaxor ferroelectric single crystals is represented by the binary PMNT system, the second generation of relaxor ferroelectric single crystals is represented by the ternary PIMNT single crystal, and the third generation of relaxor ferroelectric single crystals is represented by Mn-doped PIMNT single crystals. From the first generation to the third generation, the performance of single crystals changes from soft to hard, and a series of products are gradually formed to meet the different needs from receiving transducers to transmitting transducers. At present, it has been widely used in the field of high-end medical ultrasound imaging, and has good application prospects in the fields of underwater acoustic transducers, industrial ultrasound, piezoelectric drives, etc.

[0006] Although relaxor ferroelectric single crystals have exceptionally excellent piezoelectric properties, they are expensive. There are many reasons why relaxor ferroelectric single crystals are expensive, such as the high price of raw materials for growing single crystals, the long crystal preparation cycle, and the use of precious metal platinum crucibles for growing crystals. The cost of using a platinum crucible includes the purchase cost of platinum, the processing cost of preparing a platinum crucible, and the growth loss during crystal growth and the processing platinum crucible loss cost. The cost of using platinum exceeds 50% of the total crystal preparation cost. If the amount of platinum used can be reduced, the preparation cost of relaxor ferroelectric single crystals can be greatly reduced. Before crystal growth, the raw materials are usually prepared into rods by a tablet press or cold isostatic pressing, and then loaded into a platinum crucible for crystal growth. The density of the rods prepared by a tablet press or cold isostatic pressing is low. After the crystal growth is completed, there is still about 1 / 3 of the space on the top of the crucible that is not used, that is, the utilization rate of the platinum crucible is only about 67%. Summary of the invention

[0007] In view of the above defects in the prior art, the object of the present invention is to provide a material rod for growing relaxor ferroelectric single crystals and a preparation method and a material rod manufacturing device, which can improve the utilization rate of the crucible for growing crystals.

[0008] In a first aspect, the present invention provides a method for preparing a material rod for growing a relaxor ferroelectric single crystal, the preparation method comprising the following steps: step 1): preparing raw materials according to the stoichiometric ratio of the relaxor ferroelectric single crystal material, placing the raw materials in a raw material melting zone of a container, heating the raw material melting zone to melt the raw materials and keep them warm; step 2): then heating a casting control zone of the container, the casting control zone being connected to the raw material melting zone, so that the molten raw material remains in a molten state and flows into a mold through the casting control zone, and after cooling, a material rod for growing a relaxor ferroelectric single crystal is obtained; optionally, when the raw materials are melted and kept warm in step 1) and when the molten raw materials are flowed into the mold through the casting control zone in step 2), oxygen is introduced into the raw material melting zone.

[0009] The relaxor ferroelectric single crystal material may be undoped or doped with M atoms of lead magnesium niobate or lead titanate (chemical formula: xPb(Mg 1 / 3 Nb 2 / 3 )O3-(1-x)PbTiO3(PMNT), where 0﹤x﹤1), or undoped or doped M atoms of lead indium niobate, lead magnesium niobate, lead titanate (xPb(Mg 1 / 3 Nb 2 / 3 )O3-yPb(In 1 / 2 Nb 1 / 2 )O3-(1-xy)PbTiO3(PIMNT), wherein 0﹤x﹤1, 0﹤y﹤1, and x+y﹤1), and M is at least one of Sm, Eu, Mn, Cr, Cu, Fe, and F.

[0010] When oxygen is introduced into the raw material melting zone, the flow rate of the introduced oxygen can be set to 0.5-2 L / min, and the pressure of the gas in the container can be adjusted within the range of 0-0.3 MPa.

[0011] In the step 1), the raw material can be heated to 1300-1550° C. for 1-15 hours.

[0012] In the step 2), the casting control zone is heated to 1300-1450°C.

[0013] The material of the container can be metal platinum. The material of the mold can be steel, titanium or platinum.

[0014] If steel or titanium is used as the mold material, the mold may have a platinum foil with a thickness of 0.05 to 0.5 mm on the inner wall.

[0015] In a second aspect, the present invention provides a material rod for growing a relaxor ferroelectric single crystal, prepared by any of the above-mentioned methods for preparing a material rod for growing a relaxor ferroelectric single crystal.

[0016] In a third aspect, the present invention provides a method for preparing a relaxor ferroelectric single crystal, using the above-mentioned material rod for growing a relaxor ferroelectric single crystal to prepare the relaxor ferroelectric single crystal by a crucible descent method.

[0017] The method of the present invention is used to prepare the material rod by melt casting, which can improve the utilization rate of the platinum crucible, thereby reducing the amount of platinum, reducing the purchase cost of platinum, the growth loss during processing and growth of crystals, and the processing platinum crucible loss cost, and can greatly reduce the preparation cost of the relaxor ferroelectric single crystal. Preferably, when the raw material is melted and kept warm in step 1) and when the molten raw material flows into the mold through the casting control area in step 2), oxygen is introduced into the raw material melting area. When an appropriate amount of oxygen is introduced into the raw material melting area when heating the raw material melting area, the introduction of oxygen can increase the oxygen partial pressure in the raw material melting area on the one hand, and the high oxygen partial pressure can prevent the melt from losing oxygen when melting at high temperature. The loss of oxygen in the high temperature melt will increase the oxygen vacancies in the components. In order to achieve charge balance, the increase in oxygen vacancies will aggravate the increase in lead vacancies, resulting in a deviation between the melt component and the actual component, and ultimately causing many defects such as lead vacancies and oxygen vacancies in the grown crystal, so that the piezoelectric properties of the grown crystal are reduced (such as the piezoelectric constant d33, etc.). On the other hand, the crystals grown from the material rods prepared by the oxygen-passing process have significantly fewer defects such as internal vacancies, which significantly reduces the surface and internal cracks of the crystals. More importantly, due to the reduction of defects such as vacancies, the processed single crystal wafers, especially those with a thickness of more than 4 mm, are less broken during the heat treatment and polarization process, which ultimately improves the crystal yield. For example, the crystals grown by this process are processed into wafers with a diameter of 25 mm and a thickness of 6 mm. The wafer yield during the heat treatment and polarization process is about 10% higher than the wafer yield during the process without the oxygen-passing process. Thirdly, through the control of the oxygen-passing process, a controllable pressure can be generated in the raw material melting zone, and the casting speed can be adjusted during the casting process. The presence of positive pressure can also effectively reduce the residual melt in the container during casting. In addition, when the casting control area is heated to the specified temperature, the melt can flow down from the casting control area to cast the material rod, avoiding the dumping process of traditional material rod casting, which can effectively prevent the volatilization of materials and can also effectively avoid the human body harm caused by the volatilization of harmful substances such as lead during the casting process. In addition, the temperature of the container remains roughly the same during the entire material rod casting process, which can effectively reduce the material residue in the container of the traditional dumping process.

[0018] In a fourth aspect, the present invention provides an apparatus for manufacturing a material rod for growing a relaxor ferroelectric single crystal, the apparatus comprising a raw material melting zone and a casting control zone, the raw material melting zone having a containing portion for containing relaxor iron single crystal raw material and a first heating portion for heating the containing portion; the casting control zone comprising a casting control body for allowing the melt flow to pass through and a second heating portion for heating the casting control body, the casting control body being connected to the containing portion; the apparatus also has an air inlet portion for introducing oxygen into the containing portion. According to the structure of the device for manufacturing a material rod for growing a relaxor ferroelectric single crystal of the present invention, the first heating part can heat the raw material contained in the containing part in the form of melting and keeping it warm, and the second heating part can heat the raw material melt passing through the casting control body in the form of keeping it in a molten state, so that the molten raw material melt is discharged from the containing part through the casting control body (towards the receiving mold), which can improve the utilization rate of the platinum crucible in the manufacture of relaxor ferroelectric single crystal materials, reduce the amount of platinum, reduce the purchase cost of platinum, the growth loss during processing and growth of crystals, and the processing platinum crucible loss cost, can greatly reduce the preparation cost of relaxor ferroelectric single crystals, can prevent the melt from losing oxygen when melting at high temperature, which ultimately causes the performance of the grown crystal to be low, and can reduce the cracks on the surface and inside of the crystal grown from the prepared material rod, and ultimately improve the crystal output rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A schematic diagram showing a material rod manufacturing device used in a method for manufacturing a material rod for growing a relaxor ferroelectric single crystal according to one embodiment of the present invention;

[0020] Figure 2 The relaxor ferroelectric single crystal PMNT grown from the material rod prepared in Example 1 is shown;

[0021] Reference numerals:

[0022] 1. A material rod manufacturing device (a device for manufacturing material rods for growing relaxor ferroelectric single crystals);

[0023] A: Raw material melting zone;

[0024] B Casting control area;

[0025] 11 raw material receiving part (receiving part);

[0026] 12. Casting main body (casting control body);

[0027] 13 Gas pipelines;

[0028] 14 Gas pipelines. DETAILED DESCRIPTION

[0029] The present invention is further described by the following embodiments, and it should be understood that the following embodiments are only used to illustrate the present invention, but not to limit the present invention. In addition, the concept of direction used in the following description is used for the convenience of description, and the orientation of the structure of the invention is not limited to the direction.

[0030] The present disclosure relates to a method for preparing a material rod for the growth of a relaxor ferroelectric single crystal, which specifically includes preparing raw materials according to the stoichiometric ratio of the relaxor ferroelectric single crystal material, placing the raw materials in a raw material melting zone (hereinafter, sometimes referred to as the "upper zone") of a container, heating the raw material melting zone to melt the raw materials and keep them warm; then heating the casting control zone (hereinafter, sometimes referred to as the "lower zone") of the container, connecting the casting control zone with the raw material melting zone, allowing the molten raw material to remain in a molten state and flow into a mold through the casting control zone, and obtaining a material rod for the growth of a relaxor ferroelectric single crystal after cooling; optionally, when the raw materials are melted and kept warm and when the molten raw materials are flowed into the mold through the casting control zone, oxygen is introduced into the raw material melting zone. The present disclosure adopts a new method for preparing a material rod for the growth of a relaxor ferroelectric single crystal, which can prepare a material rod with a much higher relative density than that prepared by the tablet pressing method and the cold isostatic pressing method commonly used in the preparation of relaxor ferroelectric single crystal material rods, and can increase the utilization rate of the crucible for growing crystals to more than 85%, thereby significantly reducing the cost of crystals.

[0031] The device for manufacturing a material rod for growing a relaxor ferroelectric single crystal in one form of the present disclosure includes a raw material melting zone and a casting control zone, wherein the raw material melting zone has a housing portion for housing a relaxor iron single crystal raw material (hereinafter, sometimes referred to as a "raw material housing portion") and a first heating portion for heating the housing portion; the casting control zone includes a casting control body for allowing the melt to flow through and a second heating portion for heating the casting control body, wherein the casting control body is connected to the housing portion; the device also has an air inlet portion for introducing oxygen into the housing portion. The first heating portion can be heated in a form of melting and keeping the raw material contained in the housing portion warm, and the second heating portion can be heated in a form of keeping the raw material melt passing through the casting control body in a molten state, so that the molten raw material melt is discharged from the housing portion through the casting control body (towards a receiving mold). The raw material can be heated by the first heating portion to be fully melted and each component can be uniform, and then the lower portion can be heated to prepare the material rod. The following structure can be formed: the raw material melt heated and melted by the first heating portion can flow from the housing portion through the casting control body and be discharged to the receiving mold by its own weight and / or air pressure. Optionally, the accommodating portion has an inverted conical bottom surface, and the casting control body is connected to the lower end of the inverted conical bottom surface. Optionally, the casting control body extends in a direction intersecting the horizontal plane, or the casting control body is arranged substantially parallel to the horizontal plane. Optionally, the casting control body is formed in a round tube shape with an inner diameter of 5mm-15mm and a length of 6cm-20cm. Optionally, an opening and closing portion for opening or closing the accommodating portion and the casting control body is provided at the connection between the accommodating portion and the casting control body. Optionally, the accommodating portion is a non-open device, or the device is an open device with a cover that can open and close the accommodating portion. Optionally, the air inlet portion has a gas pipeline arranged to penetrate the accommodating portion. Optionally, the material of the accommodating portion and the casting control body is metal platinum. Optionally, the outside of the raw material melting zone and / or the casting control zone also includes a heat preservation component; and / or the first heating portion and the second heating portion include a heater, a thermocouple and a temperature controller.

[0032] The preparation is carried out by using a container (device for manufacturing a material rod for growing a relaxor ferroelectric single crystal, referred to as "material rod manufacturing device") having a raw material melting zone and a casting control zone. The raw material melting zone is provided with an open raw material receiving portion and a cover portion capable of opening and closing the raw material receiving portion, and the casting control zone is provided with a hollow casting main body portion with both ends open. One end (such as Figure 1 In addition, the material rod manufacturing device 1 may not have a cover, and the raw material melting part is a non-open device, and the pipe connected to the device is used for feeding.

[0033] Figure 1 A schematic diagram of a material rod manufacturing device used in a method for preparing a material rod for growing a relaxor ferroelectric single crystal is shown. Figure 1As shown, the material rod manufacturing device 1 comprises: an upper raw material melting zone A, including an open raw material holding portion 11, a first heating portion for heating the raw material in the raw material holding portion, and a cover portion (not shown) capable of opening and closing the raw material holding portion; and a lower casting control zone B, including a hollow casting body portion (casting control body) 12 open at both ends and a second heating portion for heating the casting body portion, wherein the upper end of the casting body portion is connected to the bottom surface of the raw material holding portion.

[0034] The material rod manufacturing device 1 is also provided with an air intake section for introducing oxygen into the raw material storage section 11. The air intake section has a gas pipeline including a gas pipeline for air intake and a gas pipeline for air exhaust. A gas pipeline 13 for introducing oxygen from a gas source (oxygen gas source) into the raw material storage section and a gas pipeline 14 for outputting gas are provided through the cover section. In a closed state (e.g., a cover closed state), the gas outlet of the gas pipeline 13 and the gas inlet of the gas pipeline 14 are located in the raw material storage section 11. Oxygen is introduced into the upper region through the air intake section. By controlling the air intake amount of the gas pipeline 13 and the air exhaust amount of the gas pipeline 14, a certain air pressure can be formed in the raw material storage section. When the raw material storage section is filled with raw material, the gas pipeline 13 is located above the raw material. The raw material storage section 11 is formed into a substantially bottomed cylindrical shape. The material rod manufacturing device 1 is configured in a form that enables the raw material melt heated and melted by the first heating section to flow from the storage section through the casting control body under the action of its own weight and / or air pressure and be discharged to the receiving mold. The bottom surface of the raw material containing part 11 is in the shape of an inverted cone, and a hole portion connected to the casting body part 12 is provided at the lower end of the cone. The cone-shaped bottom surface facilitates the migration of the melt to the bottom by its own weight and oxygen pressure. The casting body part 12 is formed into a hollow shape with open ends and a peripheral wall that can form a closed cross-section, for example, a circular tube with a circular closed cross-section. The casting body part 12 is configured so that the melt can flow to the mold by its own weight and / or oxygen pressure. The casting body part 12 is arranged substantially parallel to the horizontal plane, or is formed in the shape of a hollow tube extending in a direction intersecting the horizontal plane, which further facilitates the melt to flow through the casting body part 12 by its own weight and / or oxygen pressure. In one embodiment, the casting body 12 is arranged substantially vertically, or arranged at a certain angle to the horizontal plane, such as 85°, 80°, 75°, 70°, 65°, 60°, 55°, 50°, etc. to the horizontal plane. It should be understood that the above angle description is only exemplary and explanatory, and cannot limit the present disclosure. In one embodiment, the casting body 12 can be arranged substantially parallel to the horizontal plane, which further facilitates the melt to flow through the casting body 12 by its own weight and oxygen pressure; in one embodiment, the casting body 12 is arranged in a bent or tortuous or spiral manner, which further facilitates the melt to flow through the casting body 12 by its own weight and / or oxygen pressure. In the case where the casting body 12 is a circular tube, the inner diameter of the connecting portion between the raw material receiving portion 11 and the casting body 12 (including the hole portion on the bottom surface of the raw material receiving portion 11 and the portion of the casting body 12 at least close to the raw material receiving portion 11) can be 5mm-15mm. The length of the casting body 12 can be 6cm-20cm. The casting body 12 may have the same inner diameter at a portion relatively close to the raw material receiving portion 11 and a portion relatively far from the raw material receiving portion 11, or may have different inner diameters. Within the inner diameter and length range, the casting can be started and stopped by adjusting the temperature.In some embodiments, when the connecting portion between the casting main body 12 and the raw material containing portion 11 has a tube shape with an inner diameter of 5mm-15mm, when the molten raw material is heated in the raw material melting zone, a small portion of the raw material flows to the casting main body 12, and soon condenses and blocks the connecting portion (or the hole portion on the bottom surface of the raw material containing portion 11), and melts to become a flowable state when the casting control zone is heated to a certain temperature.

[0035] The casting body 12 and the raw material holding part 11 together serve as the container body, and the two can be formed integrally. The material of the container body can be metal platinum, which is resistant to high temperatures and can avoid being significantly corroded by the melt, and can be reused. There is a heating device on the outside of the container, and it can also have a thermal insulation support material. The first heating part is arranged outside the raw material holding part 11 to heat the raw material (upper area) in the raw material holding part. The thermal insulation support material can be arranged around the outer periphery of the raw material holding part 11. The first heating part is selected from a muffle furnace, a vertical electric furnace, etc., and the heating part includes a heater, and the heater is selected from a silicon-molybdenum heater or a silicon-carbon heater, etc. In one example, the first heating part (the upper heating device) includes a heater, a thermocouple, a temperature controller, and a wire connecting the above three. The first heating part can be formed by using a muffle furnace, etc., for example, the raw material holding part 11 and the cover part (including the gas pipeline) are arranged in the muffle furnace. The second heating part (the lower heating device) is arranged outside the casting main body 12, heats the casting main body 12 and maintains a set temperature during the casting process. The set temperature refers to the temperature for keeping the raw material in a molten state, which can be 1300-1550°C. The insulation material surrounds the outer periphery of the casting main body 12. The second heating part is selected from a muffle furnace, a vertical electric furnace, etc., and the heating part includes a heater, and the heater is selected from a silicon-molybdenum heater or a silicon-carbon heater, etc. In one example, the second heating part includes a heater, a thermocouple, a temperature controller, and a wire connecting the above three, and an appropriate amount of insulation material is surrounded by the outside of the heater.

[0036] Below the casting body 12, a mold is provided for receiving the melt from the outlet at the lower end of the casting body 12. The shape and size of the mold match the shape and size of the growing crystal. For example, a bottomed barrel mold composed of two semi-barrels with a diameter of 4 inches and a length of 150 mm (for easy demoulding) can be used. The material of the mold can be steel (high temperature resistant steel), titanium or platinum. If steel or titanium is used as the mold material, the inner wall of the mold may have a platinum foil with a thickness of 0.05 to 0.5 mm, preferably with a thickness of 0.10-0.25 mm. If steel or titanium is directly used as the mold, it may be corroded by the melt. This problem can be avoided by padding with platinum foil, and impurity contamination can be avoided. In addition, when steel and titanium are used, the amount of platinum used and the cost are less than when platinum is directly used as the mold, which is more economical.

[0037] A relaxor ferroelectric single crystal manufacturing apparatus according to one aspect of the present disclosure includes the above-mentioned apparatus for manufacturing a material rod for growing a relaxor ferroelectric single crystal.

[0038] The following is an exemplary description of the process for preparing a material rod for growing a relaxor ferroelectric single crystal according to the present invention.

[0039] First, raw materials are prepared according to the stoichiometric ratio of the relaxor ferroelectric single crystal material. The relaxor ferroelectric single crystal material can be lead magnesium niobate or lead titanate (chemical formula: xPb(Mg 1 / 3 Nb 2 / 3 )O3-(1-x)PbTiO3(PMNT), where 0﹤x﹤1), or undoped or doped M atoms of lead indium niobate, lead magnesium niobate, lead titanate (xPb(Mg 1 / 3 Nb 2 / 3 )O3-yPb(In 1 / 2 Nb 1 / 2 )O3-(1-xy)PbTiO3(PIMNT), where 0﹤x﹤1, 0﹤y﹤1, and x+y﹤1), M is at least one of Sm, Eu, Mn, Cr, Cu, Fe, and F, and the concentration of the doping element is generally less than 5%. For example, according to the stoichiometric ratio of the relaxor ferroelectric single crystal material, lead oxide and the oxides corresponding to other elements other than lead are weighed, ball-milled and mixed evenly to prepare the components of the crystal to be grown (clinker or a mixture of raw material and clinker in a certain ratio). The preparation of clinker can be divided into two steps: (1) synthesizing pre-sintered material. According to xPb(Mg 1 / 3 Nb 2 / 3 )O3-(1-x)PbTiO3(PMNT) MgO and Nb2O5 are weighed and mixed evenly by ball mill, and then pre-calcined at 900-1300℃ for 2-20h to synthesize MgNb2O6. Alternatively, according to the stoichiometric ratio of xPb(Mg 1 / 3 Nb 2 / 3 )O3-yPb(In 1 / 2 Nb 1 / 2)O3-(1-xy)PbTiO3 stoichiometric ratio of MgO, Nb2O5 and In2O3 are weighed and mixed evenly by ball mill, and then pre-fired at 900-1300℃ for 2-20h to synthesize MgNb2O6 and InNbO4. (2) Synthesizing clinker using pre-fired material. The pre-fired material and other oxides (such as TiO2 and lead oxide, etc.) weighed according to the stoichiometric ratio of relaxor ferroelectric single crystal materials are mixed evenly by ball mill, and then pre-fired at 700-1200℃ for 1-10h to prepare clinker. Lead oxide can be selected from PbO and / or Pb3O4. Oxides corresponding to other elements include TiO2, MgO, Nb2O5, In2O3, Sm2O3, Eu2O3, MnO2, Cr2O3, CuO2, Fe2O3, PbF2, etc.

[0040] Next, the raw material is loaded into the raw material holding part 11, and the raw material is heated by the upper heating device in a closed state of the upper area to melt it. The raw material is loaded into the raw material holding part 11 and the cover is closed, the upper area becomes closed, oxygen is introduced into the raw material holding part 11 through the gas pipeline 13, and oxygen is output through the gas pipeline 14. The flow rate of oxygen can be 0.5-2L / min, and the pressure of the gas in the container can be adjusted within the range of 0-0.3MPa. The raw material can be heated to 1300-1550℃, and the insulation time is 1-15 hours to fully melt the raw material. Since the relaxor ferroelectric single crystal has a complex composition, the uniformity of the castable is ensured by controlling the heating temperature and the insulation time during heating and melting. It is preferred that the insulation time is not less than 1 hour to avoid causing local unevenness of the castable and causing uneven performance of the subsequent grown crystal. The more preferred heating temperature is 1340-1440° C., and the preferred holding time is 1-6 hours. Holding at a suitable temperature for a suitable time can ensure both the quality of the molten raw material and the service life of the melting crucible.

[0041] Next, the lower area is heated to 1300-1450°C by the lower heating device, and the melt (molten raw material) in the raw material holding part 11 flows into the mold through the outlet at the lower end of the casting body 12, and after cooling, a material rod for growing a relaxor ferroelectric single crystal is obtained. The preferred heating temperature is 1330-1420°C, which can ensure both the smooth casting of the melt and the service life of the casting body. The casting of the material rod is controlled by the heating device at the bottom of the container. When the heating device is raised to a specified temperature, the melt automatically flows out, and when the heating is stopped, the melt stops flowing out.

[0042] The present invention discloses a new method for preparing a material rod for the growth of a relaxor ferroelectric single crystal, which can prepare a material rod with a much higher relative density than the commonly used tablet pressing method and cold isostatic pressing method for preparing relaxor ferroelectric single crystal material rods, and can increase the utilization rate of the crucible for growing crystals to more than 85%, which can significantly reduce the cost of crystals.

[0043] When the upper region is heated, an appropriate amount of oxygen is introduced, but oxygen may not be introduced into the container body. If the specific casting device disclosed in the present invention is used in the preparation process of the material rod, an appropriate amount of oxygen is introduced when the upper region is heated. The introduction of oxygen can increase the oxygen partial pressure in the raw material melting zone on the one hand. The high oxygen partial pressure can prevent the melt from losing oxygen when melting at high temperature. The loss of oxygen in the high-temperature melt will increase the oxygen vacancies in the components. In order to achieve charge balance, the increase in oxygen vacancies will aggravate the increase in lead vacancies, resulting in a deviation between the melt component and the actual component, and ultimately causing many defects such as lead vacancies and oxygen vacancies in the grown crystals, which reduces the piezoelectric properties of the grown crystals (such as the piezoelectric constant d33, etc.). On the other hand, the crystals grown by the material rod prepared by the oxygen-passing process have significantly fewer defects such as internal vacancies, which significantly reduces the surface and internal cracks of the crystals. More importantly, due to the reduction of defects such as vacancies, the processed single crystal wafers, especially wafers with a thickness of more than 4 mm, are less broken during the heat treatment and polarization process, which ultimately improves the crystal output rate. For example, the crystals grown by this process are processed into wafers with a diameter of 25mm and a thickness of 6mm. The wafer yield rate during the heat treatment and polarization process is about 10% higher than that of the wafers that do not use the oxygen-passing process. Thirdly, by controlling the oxygen-passing process, a controllable pressure can be generated in the raw material melting zone, and the casting speed can be adjusted during the casting process. The presence of positive pressure can also effectively reduce the residual melt in the container during casting. The casting of the material rod is controlled by the heating device at the bottom of the container. When the heating device rises to the specified temperature, the melt automatically flows out. When the heating stops, the melt stops flowing out. This control process can effectively avoid the volatilization of relaxor ferroelectric single crystal materials and the residue of materials in the container caused by the pouring process used in traditional casting. In addition, it can also effectively avoid human harm caused by the volatilization of harmful substances such as lead.

[0044] Preparation of relaxor ferroelectric single crystals.

[0045] Using the prepared growth relaxor ferroelectric single crystal material rod and platinum crucible, a relaxor ferroelectric single crystal is prepared by a crucible descent method. The crucible descent method may include: taking the growth relaxor ferroelectric single crystal material rod obtained above out of the mold, placing it in a crucible, and growing the crystal. The crystal growth process parameters are detailed in Chinese invention patent ZL201310352429.2.

[0046] The following further examples are given to illustrate the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention belong to the scope of protection of the present invention. The specific process parameters and the like in the following examples are also only examples within a suitable range, that is, those skilled in the art can make a selection within a suitable range through the description herein, and are not limited to the specific values ​​​​exemplified below.

[0047] In the following examples, the reagents, materials and instruments used are conventional reagents, conventional materials and conventional instruments unless otherwise specified, and are all commercially available. The reagents involved can also be synthesized by conventional synthesis methods.

[0048] Example 1

[0049] According to the crystal 0.68Pb(Mg 1 / 3 Nb 2 / 3 )The raw materials (TiO2, MgO, Nb2O5 and PbO) prepared in the stoichiometric ratio of 0.12PbTiO3-0.32PbTiO3 are placed in a platinum container and the lid of the container is closed. The flow rate of oxygen is 0.8L / min. The oxygen pressure is 0 when the material rod is prepared. When the material rod is prepared to 50% by weight, the oxygen pressure is adjusted to 0.2MPa. The raw materials are heated to 1340℃ by the upper heating device and kept warm for 6 hours until all the raw materials are melted and mixed evenly. The lower area is heated to 1400℃ by the lower heating device, and the melt flows into a mold with a diameter of 3 inches and a length of 180mm made of metal titanium through the lower outlet. The inner wall of the mold is padded with a layer of 0.10mm thick platinum foil. After cooling, the material rod for growing relaxor ferroelectric single crystals is obtained. The material rod is placed in a 3-inch platinum crucible and placed in a crucible descending furnace for crystal growth. The utilization rate of the platinum crucible reaches 88%. Figure 2 The crystal grown from the rod prepared by the above process is shown in Table 1.

[0050] Example 2

[0051] According to the crystal 0.42Pb(Mg 1 / 3 Nb 2 / 3 )O3-0.25Pb(In 1 / 2 Nb 1 / 2)O3-0.33PbTiO3 stoichiometric ratio of raw materials (TiO2, MgO, Nb2O5, In2O3 and Pb3O4), put into a platinum container and cover the container, oxygen flow rate is 1L / min, oxygen pressure is 0.1MPa when starting to prepare the material rod, and oxygen pressure is adjusted to 0.2MPa when the material rod is prepared to 80% by weight. The raw materials are heated to 1400℃ by the upper heating device and kept warm for 3h until all the raw materials are melted and mixed evenly. The lower area is heated to 1330℃ by the lower heating device, and the melt flows into a mold with a diameter of 4 inches and a length of 160mm made of high-temperature resistant steel through the lower outlet. The inner wall of the mold is padded with a layer of 0.25mm thick platinum foil. After cooling, the material rod for growing relaxor ferroelectric single crystal is obtained. The crystal is grown using this material rod, and the preparation process of the crystal is consistent with the growth process conditions in Example 2 of Chinese invention patent ZL201310352429.2. The utilization rate of the platinum crucible reached 90%. The performance test data of the crystal are shown in Table 1.

[0052] Example 3

[0053] According to the crystal 0.71Pb 0.9775 Sm 0.015 (Mg 1 / 3 Nb 2 / 3 )O3-0.29Pb 0.9775 Sm 0.015 The raw materials (TiO2, MgO, Nb2O5, Sm2O3 and PbO and Pb3O4 with a molar ratio of 1:1) prepared with the stoichiometric ratio of TiO3 are placed in a platinum container and the lid of the container is closed. The oxygen flow rate is 0.5L / min, and the oxygen pressure is maintained at 0.15MPa during the preparation of the material rod. The raw materials are heated to 1300℃ by the upper heating device and kept warm for 12 hours until all the raw materials are melted and mixed evenly. The lower area is heated to 1440℃ by the lower heating device, and the melt flows into a mold with a diameter of 3 inches and a length of 180mm prepared by metal platinum through the lower outlet. After cooling, the material rod for growing relaxor ferroelectric single crystals is obtained. This material rod is used for crystal growth. The utilization rate of the platinum crucible reaches 85%.

[0054] Example 4

[0055] According to the crystal 0.38Pb[Mn 0.01 (Mg 1 / 3 Nb 2 / 3 ) 0.9925 ]O3-0.26Pb[Mn 0.01 (In 1 / 2 Nb 1 / 2 ) 0.9925 ]O3-0.36Pb[Mn 0.01 Ti0.9925 ]O3 stoichiometric ratio of raw materials (TiO2, MgO, Nb2O5, In2O 3、 MnO2 and PbO), put them into a platinum container and cover the lid of the container. The flow rate of oxygen is 2L / min. The oxygen pressure is 0.05 when the material rod is prepared. When the material rod is prepared to 70% by weight, the oxygen pressure is adjusted to 0.25MPa. The raw materials are heated to 1550℃ by the upper heating device and kept warm for 1h until all the raw materials are melted and mixed evenly. The lower area is heated to 1300℃ by the lower heating device, and the melt flows into a mold with a diameter of 4 inches and a length of 160mm made of metal titanium through the lower outlet. After cooling, the material rod for growing relaxor ferroelectric single crystals is obtained. Use this material rod for crystal growth. The utilization rate of the platinum crucible reaches 92%. The performance test data of the crystal are shown in Table 1.

[0056] Example 5

[0057] According to the crystal 0.60Pb[Fe 0.08 (Mg 1 / 3 Nb 2 / 3 ) 0.994 ]O3-0.40Pb[Fe 0.08 Ti 0.994 ]O3 in a stoichiometric ratio (TiO2, MgO, Nb2O5, Fe2O3 and PbO and Pb3O4 in a molar ratio of 2:1), are placed in a platinum container and the lid of the container is closed. The flow rate of oxygen is 1.6L / min. The oxygen pressure is 0 when the material rod is prepared. When the material rod is prepared to 75% by weight, the oxygen pressure is adjusted to 0.3MPa. The raw materials are heated to 1440℃ by the upper heating device and kept warm for 2h until all the raw materials are melted and mixed evenly. The lower area is heated to 1420℃ by the lower heating device, and the melt flows into a mold made of high-temperature resistant steel with a diameter of 4 inches and a length of 160mm through the lower outlet. The inner wall of the mold is padded with a layer of 0.15mm thick platinum foil. After cooling, the material rod for growing relaxor ferroelectric single crystals is obtained. Using this material rod for crystal growth, the utilization rate of the platinum crucible reaches 90%.

[0058] Table 1 Properties of relaxor ferroelectric single crystals with different compositions

[0059]

[0060] Test method: The piezoelectric performance test refers to the national standard GB / T3389-2008 "Test method for performance parameters of piezoelectric ceramic materials".

[0061] Comparative Example

[0062] The raw material prepared in Example 1 was selected and a material rod was prepared by cold isostatic pressing. The pressure of the cold isostatic pressing was 200 MPa, the holding time was 5 minutes, the diameter of the material rod was 3 inches, and the length was 180 mm. This material rod was used for crystal growth, and the utilization rate of the platinum crucible was 60%. The raw material prepared in Example 1 was selected and a material rod was prepared by a tablet press. The pressure of the tablet press was 200 MPa, the holding time was 5 minutes, the diameter of the material rod was 3 inches, the length was 60 mm, and the height was 45 mm. A total of 5 material blocks were pressed, with a total height of 180 mm. This material rod was used for crystal growth, and the utilization rate of the platinum crucible was 65%.

Claims

1. A method for preparing a material rod for growing a relaxor ferroelectric single crystal, characterized in that: The preparation method comprises the following steps: Step 1): preparing raw materials according to the stoichiometric ratio of the relaxor ferroelectric single crystal material, placing the raw materials in a raw material melting zone of a container, heating the raw material melting zone to melt the raw materials, and keeping the temperature; Step 2): heating the casting control area of ​​the container, the casting control area is connected to the raw material melting area, so that the molten raw material remains in a molten state, flows into the mold through the casting control area, and obtains a material rod for the growth of relaxor ferroelectric single crystal after cooling; When the raw material is melted and kept warm in step 1) and when the molten raw material flows into the mold through the casting control zone in step 2), oxygen is introduced into the raw material melting zone.

2. The preparation method according to claim 1, characterized in that: The relaxor ferroelectric single crystal material is lead magnesium niobate, lead titanate, or lead indium niobate, lead magnesium niobate, or lead titanate, which is undoped or doped with M atoms, and M is at least one of Sm, Eu, Mn, Cr, Cu, Fe, and F.

3. The preparation method according to claim 1, characterized in that: When oxygen is introduced into the raw material melting zone, the flow rate of the introduced oxygen is 0.5 to 2 L / min, and the pressure of the gas in the container is adjustable within the range of 0 to 0.3 MPa.

4. The preparation method according to claim 1, characterized in that: In the step 1), the raw material is heated to 1300-1550° C. and kept at this temperature for 1-15 hours.

5. The preparation method according to claim 1, characterized in that: In the step 2), the casting control zone is heated to 1300-1450°C.

6. The preparation method according to any one of claims 1 to 5, characterized in that The material of the container is metal platinum.

7. A material rod for growing a relaxor ferroelectric single crystal prepared by the method for preparing a material rod for growing a relaxor ferroelectric single crystal according to any one of claims 1 to 6.

8. A method for preparing a relaxor ferroelectric single crystal, characterized in that: The relaxor ferroelectric single crystal is prepared by a crucible descent method using the material rod for growing a relaxor ferroelectric single crystal as claimed in claim 7.

9. A device for manufacturing a material rod for growing a relaxor ferroelectric single crystal, characterized in that: The device comprises a raw material melting zone and a casting control zone, wherein the raw material melting zone comprises a receiving portion for receiving relaxor iron single crystal raw material and a first heating portion for heating the receiving portion; the casting control zone comprises a casting control body for allowing the melt flow to pass through and a second heating portion for heating the casting control body, wherein the casting control body is connected to the receiving portion; The device is also provided with an air inlet portion for introducing oxygen into the containing portion; The casting control body is formed in a round tube shape with an inner diameter of 5 mm to 15 mm and a length of 6 cm to 20 cm; An opening and closing portion for opening or closing the accommodating portion and the casting control body is provided at a connection between the accommodating portion and the casting control body.

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