CN1763264A

CN1763264A - Flux method for growth of gallium phosphate crystal

Info

Publication number: CN1763264A
Application number: CN 200510044842
Authority: CN
Inventors: 王继扬; 李静; 梁曦敏
Original assignee: Shandong University
Current assignee: Shandong University
Priority date: 2005-10-08
Filing date: 2005-10-08
Publication date: 2006-04-26
Anticipated expiration: 2025-10-08
Also published as: CN100350081C

Abstract

The present invention is fluxing agent growth process of gallium phosphate crystal. Through using lithium carbonate and molybdenum oxide as flux, gallium oxide and ammonium dihydrogen phosphate as main material, mixing ammonium dihydrogen phosphate, gallium oxide, lithium carbonate and molybdenum oxide in the weight ratio of 1 to 1.23 to 1.12 to 6.57, setting the mixture in platinum crucible, heating to melt inside growth furnace and cooling to the temperature of 10-20 deg.c over the solution saturation point to obtain the mixed melt of gallium phosphate and the flux, introducing seed crystal into the growth furnace, lowering the temperature to 1-2 deg.c over the solution saturation point when the seed crystal begins to melt and rotating the seed crystal in 30 rpm for 24 hr, gallium phosphate crystal is grown. After lowering the temperature, the crystal is taken out of the solution. The process can eliminate water from the crystal and raise the piezoelectric performance of the crystal.

Description

Flux growth method of gallium phosphate crystal

The technical field is as follows:

the invention relates to gallium phosphate (GaPO)₄) A method for growing crystals.

(II) background technology:

the piezoelectric crystal has stable electromechanical performance and small transmission loss, and is an important functional material. The piezoelectric resonator, piezoelectric transducer and piezoelectric sensor prepared by the method are used for communication, electroacoustic, underwater acoustic, ultrasonic,The application in the fields of aviation, medical treatment and the like is wide. There are three major types of piezoelectric crystal materials that have been widely used and form the industry in the information industry: quartz (SiO)₂) Lithium niobate (LiNbO)₃) And lithium tantalate (LiTaO)₃)。

The quartz crystal has very good temperature stability and zero temperature coefficient tangent (ST-cut type), and is insoluble in other acid and alkali solutions except hydrofluoric acid. The quartz crystal is used in the field of piezoelectric materials for high-temperature surface acoustic wave and bulk wave devices. From the stability point of view, there is no material which is comparable to quartz crystals. But the electromechanical coupling coefficient of quartz crystal 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.

The lithium niobate and lithium tantalate crystals have similar structures and performances, are insoluble in water and have stable chemical properties. The coupling factor of lithium niobate is very large (K)²0.055) but has a large temperature coefficient and does nothave a zero temperature coefficient cut. The temperature stability of lithium tantalate is better than that of lithium niobate crystal, but zero temperature coefficient cut does not exist, and the electromechanical coupling factor is less than one fourth of that of lithium niobate.

In order to meet the needs of the information industry which is rapidly developing at present, a novel piezoelectric material becomes a hotspot of the research in the field of materials at present.

Gallium phosphate (GaPO)₄) The crystal structure of the quartz crystal is similar to α -quartz and is a quartz-like crystal, compared with quartz, gallium phosphate has better characteristic, no phase change of α - β quartz exists, the good characteristic can be kept stable, the thermal stability, the piezoelectric coefficient and the electromechanical coupling coefficient of the quartz crystal are much higher than those of the quartz crystal, and the quartz crystal has the advantages of the quartz crystal, such as no first-order thermoelectricity, temperature compensation cut type required by a piezoelectric oscillator and a filter, high resistivity and the like.

At present, a hydrothermal method is always adopted to grow GaPO₄And (4) crystals. Generally, phosphoric acid (H) is used₃PO₄) As medium solution, and phosphoric acid (H) as culture medium₃PO₄) And gallium (Ga). Putting the raw materials into a high-pressure kettle, charging into a furnace, heating to melt the materials for crystal growth, wherein the heating speed is 1-3.5 ℃/day generally, and the heating interval is 180-230 ℃ to 230 ℃. Although the hydrothermal method can stably grow a single crystal, GaPO has been used in recent years₄The hydrothermal growth of the crystal does not make a great breakthrough.

Growth of GaPO by hydrothermal method₄The main defect of the crystal is due to the existence of water and OH in the crystal^-The groups are difficult to remove, and the ordered/disordered polarizability of the medium function at the low frequency of the crystal is reduced. GaPO₄The dielectric constant of the crystal is substantially determined by OH in the crystal^-The content of (a). The measurement of the temperature range between-160 ℃ and 200 ℃ shows that^T ₁₁There is a strong dependence on temperature, which decreases with increasing frequency. 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.

(III) the invention content:

aiming at the defects of the prior art, the invention provides a fluxing agent growth method of gallium phosphate crystal, which can effectively eliminate the water content in the crystal. The method can also avoid expensive hydrothermal device and high pressure container; the consumption and consumption of noble metal are reduced.

The solution adopted by the invention is as follows:

the method for growing the gallium phosphate crystal by using the fluxing agent takes lithium carbonate and molybdenum oxide as the fluxing agent, takes 2N-5N gallium oxide and ammonium dihydrogen phosphate as raw materials, weighs ammonium dihydrogen phosphate, gallium oxide, lithium carbonate and molybdenum oxide according to the weight ratio of 1: 1.23: 1.12: 657, puts the raw materials into a crystal incubator after being uniformly mixed, heats the raw materials 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 surface for preheating, then placing the seed crystals into a mixed melt of gallium phosphate and a fluxing agent, reducing the temperature to 1-2 ℃ above the saturation point after the seed crystals start to melt, simultaneously rotating the seed crystals in a forward rotation-stop-reverse rotation circulation mode at a rotation rate of 30 revolutions per minute, and cooling after 24 hours, wherein the cooling rate is increased from 0.2-0.4 ℃/day in the initial growth stage to 1-2 ℃/day in the later stage; after 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 invention adopts a fluxing agent method to grow GaPO₄The crystal can effectively eliminate the water content in the crystal and improve GaPO₄Piezoelectric properties of the crystal.

(IV) description of the drawings

FIG. 1 is a schematic view showing the structure of a growth and control apparatus for growing a crystal according to the present invention.

FIG. 2 shows GaPO prepared by the present invention₄The infrared absorption spectrum of the crystal.

Wherein: 1. rotating device, 2, seed crystal rod, 3, refractory brick, 4, furnace tube, 5, resistance wire, 6, heat insulating material, 7, crystal incubator, 8, molten liquid, 9, alumina crucible, 10 and thermocouple

(V) specific embodiment:

FIG. 1 shows GaPO growth using the present invention₄The device structure of the crystal is shown schematically. The device is a vertical resistance wire heating furnace, a seed crystal rod 2 extends into a melt 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-molybdenum oxide (Li) is selected₂CO₃＿MoO₃) As fluxing agent, the raw material is gallium oxide (Ga) of 2N-5N₂O₃) And ammonium dihydrogen phosphate (NH)₄H₂PO₄) The above-mentioned various reagents are mixed according to ammonium dihydrogen phosphate and oxygenThe weight ratio of gallium oxide, lithium carbonate and molybdenum oxide is 1: 1.23: 1.12: 6.57, the materials are strictly weighed, and after being uniformly mixed, the materials are put into a crystal incubator 7, namely a platinum crucible, and the temperature is raised to 1000-1050 ℃ for melting and melting. Keeping the temperature for more than 24 hours to ensure that the materials are fully melted and then stirring the materials to ensure that the solution is fully and uniformly mixed, and then cooling the solution to be 10-20 ℃ above the saturation point temperature of the solution to obtain a mixed melt of gallium phosphate and the fluxing agent; the solute concentration is 10-50%.

The chemical reaction equation is as follows:

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

measuring the saturation point temperature of the solution by a seed crystal heuristic method, selecting the seed crystal with better quality for growing, slowly introducing the seed crystal into a growing furnace when the temperature is 10-20 ℃ higher than the saturation point temperature of the solution, putting the seed crystal at a proper position above the liquid level for fully preheating, then putting the seed crystal into the solution, reducing the temperature to 1-2 ℃ above the saturation point, and rotating at a rotation rate of 30 revolutions per minute according to a circulation mode of forward rotation, stop rotation and reverse rotation. The temperature is reduced after 24 hours, the temperature reduction rate is continuously accelerated along with the growth of the crystal, and the temperature is increased from 0.2-0.4 ℃/day in the initial growth stage to 1-2 ℃/day in the later stage. The growth period is about 50 d. After the growth is finished, the crystal is extracted from the solution, and is naturally cooled to room temperature after being cooled to 200 ℃ at the cooling rate of 30 ℃/hour. The cooling process lasts for about 2-3 days. The obtained centimeter-sized GaPO has complete crystal form₄And (4) crystals. The infrared absorption spectrum of the crystal was measured by KBr pellet method (see FIG. 2). No OH is found in the infrared band^-Obviously absorbing the clusters, growing GaPO by a fluxing agent method₄The crystal effectively eliminates the existence of water inside the crystal. The method can also avoid expensive hydrothermal device and high pressurecontainer; the consumption and consumption of noble metal are reduced.

Claims

1. A flux growth method of gallium phosphate crystal is characterized in that: the method comprises the steps of taking lithium carbonate and molybdenum oxide as fluxing agents, taking 2N-5N gallium oxide and ammonium dihydrogen phosphate as raw materials, weighing ammonium dihydrogen phosphate, gallium oxide, lithium carbonate and molybdenum oxide according to the weight ratio of 1: 1.23: 1.12: 657, uniformly mixing, putting into a crystal incubator, heating in a growth furnace to 1000-1050 ℃ for melting, keeping the temperature for more than 24 hours, and cooling to 10-20 ℃ above the saturation point temperature of the solution to obtain a mixed melt of gallium phosphate and the fluxing agents; 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 surface for preheating, then placing the seed crystals into a mixed melt of gallium phosphate and a fluxing agent, reducing the temperature to 1-2 ℃ above the saturation point after the seed crystals start to melt, simultaneously rotating the seed crystals in a forward rotation-stop-reverse rotation circulation mode at a rotation rate of 30 revolutions per minute, and cooling after 24 hours, wherein the cooling rate is increased from 0.2-0.4 ℃/day in the initial growth stage to 1-2 ℃/day in the later stage; after 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.