CN1872670A

CN1872670A - Method for developing crystal of aluminium phosphate through cosolvent

Info

Publication number: CN1872670A
Application number: CN 200610044988
Authority: CN
Inventors: 王继扬; 李静; 梁曦敏
Original assignee: Shandong University
Current assignee: Shandong University
Priority date: 2006-06-26
Filing date: 2006-06-26
Publication date: 2006-12-06
Anticipated expiration: 2026-06-26
Also published as: CN100363253C

Abstract

This invention provides a method for growing aluminum phosphate. The method uses aluminum oxide and ammonium dihydrogen phosphate as the raw materials, and lithium carbonate and ammonium dihydrogen phosphate as the fusing agents. The method comprises: (1) mixing the raw materials and the fusing agents in a crystal-growing container; (2) heating for melting, keeping the temperature for more than 24 h, and cooling to 10-20 deg.C above the saturation point of the melt; (3) introducing the seed crystal, and cooling to 1-2 deg.C above the saturation point; (4) rotating at 30 rpm, cooling at a rate of 0.2-0.4 deg.C/d to 1-2 deg.C/d, terminating the growth 45-50 days later, and pulling out the crystals; (5) cooling at a rate 30 deg.C/h to 200 deg.C, and naturally cooling to room temperature. The method can effectively eliminate water in the aluminum phosphate crystals, and can improve the piezoelectric property of the crystals.

Description

Method for growing aluminum phosphate crystal by fluxing agent

Technical Field

The invention relates to AlPO₄The growing method of (aluminium phosphate) crystal belongs to AlPO₄The technical field of crystal growth.

Background

The piezoelectric crystal has stable electromechanical performance and small transmission loss, and is an important electronic functional material. The piezoelectric resonator, the piezoelectric transducer and the piezoelectric sensor prepared from the material have wide application in the fields of communication, electroacoustic, underwater acoustic, ultrasonic, aviation, medical treatment and the like. Quartz crystals have been widely used and form the industry in the information industry field. The quartz crystal has very good temperature stability and zero temperature coefficient tangent (ST cutting type), and is insoluble in other acid and alkali solutions except hydrofluoric acid. In the field of piezoelectric materials for high-temperature surface acoustic wave and bulk wave devices, the quartz crystal is almost the same day. From the stability point of view, there is no material which is comparable to quartz crystals. But the electromechanical coupling factor of the quartz transistor is small (K)²0.001), the surface acoustic wave device and the bulk wave device made of the material have the defects of small bandwidth and large difference loss. In order to meet the requirements of modern digital communication technology which is rapidly developed at present, the research of novel piezoelectric materials becomes a hotspot of the research in the field of materials at present.

AlPO4 (aluminum phosphate) has a crystal structure similar to α -quartz and is a quartz-like crystal, compared with quartz, AlPO4 has better characteristics, the electromechanical coupling coefficient is 2-4 times larger than that of quartz in the application of bulk waves and surface acoustic waves, and the crystal can be used for manufacturing bulk wave and surface acoustic wave devices, voltage-controlled oscillators, temperature compensation crystal oscillators and the like in addition to the bulk wave resonators, the Y rotation cut theta angle is-38-30, compared with the performance of the same cut angle of quartz, the frequency temperature performance of the crystal is better than that of quartz except that AT is similar to BT cut type, and the angle sensitivity of the temperature coefficient of quartz is better.

Researchers have been using hydrothermal methods to grow AlPO4 crystals. The main defect of the hydrothermal growth method is that the existence of OH in the crystal is difficult to avoid^-And thus the dielectric polarizability of the crystal. Hydrothermal method for growing AlPO₄Crystals, typically phosphoric acid (H)₃PO₄) As medium solution, and phosphoric acid (H) as culture medium₃PO₄) And alumina (Al)₂O₃). The growth conditions in phosphoric acid were 6.1M phosphoric acid concentration and the growth zone start temperature was 151 ℃. The temperature difference between the growth area and the nutrition area is 2.5 DEG CThe temperature rise speed is 1.6-2 ℃/day, and the temperature of the growth area is 200 ℃ when the growth is finished.

Hydrothermal method for growing AlPO₄The main defect of the crystal is due to the existence of water and OH in the crystal^-The radicals are difficult to remove, reducing the quality factor of the crystal. Meanwhile, the hydrothermal growth method requires high-temperature and high-pressure conditions, the consumption of noble metal linings is large, the requirement on equipment is high, and the method is not favorable for large-scale production. Due to the limitations of the hydrothermal method, which is a growth method, it is difficult to minimize the water content in the crystal. AlPO in recent years₄The hydrothermal growth of the crystal does not make a great breakthrough.

Disclosure of Invention

Aiming at the defects of the existing hydrothermal method for growing AlPO4 crystal, the invention provides a method which can effectively eliminate the water content in the crystal and improve the AlPO₄Piezoelectric performance of the crystal, and a method for growing aluminum phosphate crystal by using a complete crystal form.

The method for growing the aluminum phosphate crystal by the fluxing agent comprises the following steps:

taking lithium carbonate and ammonium dihydrogen phosphate as fluxing agents, taking 2N-5N aluminum oxide and ammonium dihydrogen phosphate as raw materials, weighing the ammonium dihydrogen phosphate, the aluminum oxide, the lithium carbonate and the ammonium dihydrogen phosphate according to the weight ratio of 1: 2.25: 6.44: 15.5, uniformly mixing, putting into a crystal incubator, heating in a growth furnace to 1000-; introducing seed crystals into a growth furnace when the temperature is 10-20 ℃ higher than the saturation point of the solution, placing the seed crystals above the liquid level for preheating, then placing the seed crystals into a mixed melt of aluminum phosphate and a fluxing agent, after the seed crystals begin to melt, reducing the temperature to 1-2 ℃ higher than the saturation point, simultaneously rotating the seed crystals in a forward rotation-stop-reverse rotation circulating mode at a rotation rate of 30 revolutions per minute, and after 24 hours, beginning to reduce the temperature, wherein the temperature reduction rate is increased from 0.2-0.4 ℃/day at the initial growth stage to 1-2 ℃/day at the later stage; after 45-50 days, the growth is finished, the crystal is extracted from the solution, cooled to 200 ℃ at the cooling rate of 30 ℃/hour, and naturally cooled to room temperature.

The method for growing AlPO by adopting fluxing agent₄The crystallization is carried out under high temperature condition, and AlPO can be effectively eliminated by adopting the method₄The existence of water in the crystal improves the piezoelectric performance of the crystal. AlPO grown by flux method₄The crystal is complete in crystal form, and no OH is found in the infrared band^-Apparent absorption of the clusters.

Drawings

The attached drawing is a structural schematic diagram of a growing furnace for growing crystals by adopting the invention.

In the figure: 1. the device comprises a rotating device, 2, a seed crystal rod, 3, refractory bricks, 4, a furnace tube, 5, a resistance wire, 6, a heat insulating material, 7, a crystal incubator, 8, molten liquid, 9, an alumina crucible, 10 and a thermocouple.

Detailed Description

Examples

The attached figure shows the growth of AlPO by the method of the invention₄The structure of the crystal growing furnace is shown schematically. The growth furnace is a vertical resistance wire heating furnace, a seed crystal rod 2 extends into a molten liquid 8 and rotates under the drive of a rotating device 1, a refractory brick 3 is arranged in a furnace tube 4, a resistance wire 5 is wound on the outer wall of the furnace tube 4, and the outer layer of the resistance wire is made of a heat insulation material 6. The temperature control equipment is an FP21 type programmable automatic temperature controller, and the temperature control precision in the growth temperature region is 0.1 percent. The crystal grower 7 is placed in an alumina crucible 9, is a platinum crucible with the thickness of 70 multiplied by 90mm, can bear the working temperature below 1774 ℃, and is not easy to be corroded by contained melt. The thermocouple 10 uses PtRh/Pt, which can effectively control the growth temperature.

Lithium carbonate-ammonium dihydrogen phosphate (Li) is selected₂CO₃-NH₄H₂PO₄) As fluxing agent, the solute concentration is 15%, and the raw materials are high-purity 2N-5N alumina and ammonium dihydrogen phosphate (Al)₂O₃、NH₄H₂PO₄) The reagents are strictly weighed according to the weight ratio of ammonium dihydrogen phosphate, alumina, lithium carbonate and ammonium dihydrogen phosphate of 1: 2.25: 6.44: 15.5,after being uniformly mixed, the mixture is put into a crystal incubator 7, the temperature is raised to 1000 ℃ to 1050 ℃ for melting the materials, the temperature is kept for more than 24 hours, the materials are fully melted and then stirred, so that the solution is fully and uniformly mixed; and then cooling to 10-20 ℃ above the saturation point temperature of the solution to obtain a mixed melt of aluminum phosphate and the fluxing agent.

The chemical reaction equation is as follows:

the reaction equation of the fluxing agent system is as follows:

the method comprises the steps of measuring the saturation point temperature of a solution by using a seed crystal heuristic method, selecting a seed crystal with good quality for growth, slowly introducing the seed crystal into a growth furnace when the temperature is 10-20 ℃ higher than the saturation point temperature, placing the seed crystal at a proper position above a liquid level for fully preheating, and then putting the seed crystal into the solution, keeping the seed crystal for a period of time and slightly melting the seed crystal so as to ensure that the end surface of the seed crystal, which is in contact with the solution, has a layer of fresh atomic surface, and avoiding the extension of defects such as mechanical defects, dislocation and the like. The temperature was then lowered to 1-2 ℃ above the saturation point and rotated at a rotation rate of 30 revolutions per minute in a cyclic manner of forward-stop-reverse rotation (such rotation being beneficial to the growth of the crystal faces). The temperature is reduced after 24 hours, the temperature reduction rate is continuously accelerated along with the growth of the crystal, the temperature is increased from 0.2-0.4 ℃/day in the initial growth stage to 1-2 ℃/day in the later growth stage, and the growth period is 50 days. And after the growth is finished, extracting the crystal from the solution, cooling to 200 ℃ at a cooling rate of 30 ℃/hour, naturally cooling to room temperature, and keeping the cooling process for about 2-3 days. Since the crystal grown by flux method is discharged from the furnace at high temperature, the cooling rate at this stage must be slow. Thus, crystal cracking caused by thermal stress can be avoided, and the integrity of the crystal is maintained. AlPO with complete crystal form is obtained by the method₄Crystal, no OH is found in infrared band^-Apparent absorption of the clusters.

Claims

1. A method for growing aluminum phosphate crystals by using a fluxing agent is characterized by comprising the following steps: taking lithium carbonate and ammonium dihydrogen phosphate as fluxing agents, taking 2N-5N aluminum oxide and ammonium dihydrogen phosphate as raw materials, weighing the ammonium dihydrogen phosphate, the aluminum oxide, the lithium carbonate and the ammonium dihydrogen phosphate according to the weight ratio of 1: 2.25: 6.44: 15.5, uniformly mixing, putting into a crystal incubator, heating in a growth furnace to 1000-; introducing seed crystals into a growth furnace when the temperature is 10-20 ℃ higher than the saturation point of the solution, placing the seed crystals above the liquid level for preheating, then placing the seed crystals into a mixed melt of aluminum phosphate and a fluxing agent, after the seed crystals begin to melt, reducing the temperature to 1-2 ℃ higher than the saturation point, simultaneously rotating the seed crystals in a forward rotation-stop-reverse rotation circulating mode at a rotation rate of 30 revolutions per minute, and after 24 hours, beginning to reduce the temperature, wherein the temperature reduction rate is increased from 0.2-0.4 ℃/day at the initial growth stage to 1-2 ℃/day at the later stage; after 45-50 days, the growth is finished, the crystal is extracted from the solution, cooled to 200 ℃ at the cooling rate of 30 ℃/hour, and naturally cooled to room temperature.