At&t Bell Laboratories

Bell Telephone Laboratories

Ernest D Kolb

Robert A Laudise

Anthony J Caporaso

High quality crystals of materials that are essentially silicon-free are produced in a low pressure hydrothermal growth process through a specific expedient. In particular, the aqueous solution utilized in the pressure vessel during growth is introduced in significantly larger quantities than previously thought to be acceptable.

Hydrothermal crystal growth processes

AlPO.sub.4 crystals are isomorphic with quartz and are expected therefore to have several crystal orientations in which the elastic (piezoelectric) constants are relatively insensitive to temperature. The piezoelectric coupling coefficients of AlPO.sub.4 are approximately three times those of quartz. Hydrothermal growth techniques to date have been marginal, and all have employed H.sub.3 PO.sub.4 as the hydrothermal solution. We describe using HCl as the hydrothermal solution and demonstrate the superiority of HCl from the standpoint of solubility and consequent crystal growth rate.

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New Providence, NJ, United States of America

Ernest D Kolb