Hydrothermal crystal growing process and apparatus
AssigneeAllied Corporation
InventorsBruce H. Chai, Ernest Buehler, John J. Flynn
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Abstract
Large single crystals of berlinite are grown onto seed crystals by maintaining the crystals at a fixed elevated temperatutre in a pressure vessel containing a nutrient of coarse berlinite crystalline powder, held at a fixed lower temperature, and concentrated phosphoric acid. Because berlinite shows retrograde solubility, the nutrient goes into solution, and berlinite deposits on the higher-temperature growing crystal. The vessel is rocked to promote motion of saturated solution to the crystal and depleted solution to the nutrient. Large single crystals of alpha-gallium orthophoshate may be grown using the same apparatus and a similar process. The resultant crystals may be cut into wafers useful in surface acoustic wave devices.
Claims21
A process for growing single crystals of a metal orthophosphate selected from the group consisting of alpha-aluminum orthophosphate and alpha-gallium orthophosphate, comprising the steps of:
- (a) suspending a seed crystal of the metal orthophosphate in a first chamber of a substantially horizontally-oriented pressure vessel, said first chamber being partitioned from at least one additional chamber so that a temperature gradient can be maintained and fluid can flow between the chambers,
- (b) introducing into a second chamber of the vessel a quantity of coarse crystalline powder of the metal orthophosphate,
- and then, sequentially,
- (c) partially filling the vessel with concentrated phosphoric acid,
- (d) sealing the vessel,
- (e) heating the vessel to achieve a seed crystal temperature in the range from about 135.degree. C. to 210.degree. C. and a powder temperature about 5.degree. C. to 30.degree. C. lower,
- (f) maintaining the temperatures in the vessel while rocking the vessel about a horizontal axis to raise first one chamber of the vessel and then another, whereby the seed crystal grows from an acid solution of the metal orthophosphate,
- (g) cooling the vessel to near ambient temperature, and
- (h) recovering the resultant single crystal.
A process for growing single crystals of a metal orthophosphate selected from the group consisting of alpha-aluminum orthophosphate and alpha-gallium orthophosphate, comprising the steps of:
- (a) suspending a seed crystal of the metal orthophosphate in a first chamber of a substantially horizontally-oriented pressure vessel, said first chamber being partitioned from at least one additional chamber so that a temperature gradient can be maintained and fluid can flow between the chambers,
- (b) introducing into a second chamber of the vessel a quantity of coarse crystalline powder of the metal orthophosphate,
- and then, sequentially,
- (c) sealing the vessel,
- (d) heating the vessel to achieve a seed crystal temperature in the range from about 135.degree. C. to 210.degree. C. and a powder temperature about 5.degree. C. to 30.degree. C. lower,
- (e) partially filling the vessel with concentrated phosphoric acid,
- (f) maintaining the temperatures in the vessel while rocking the vessel about a horizontal axis to raise first one chamber of the vessel and then another, whereby the seed crystal grows from an acid solution of the metal orthophosphate,
- (g) cooling the vessel to near ambient temperature, and
- (h) recovering the resultant single crystal.
Dependencies are inferred from the claim text.