Large High Quality Single Crystal Aluminum Phosphate for Acoustic Wave Devices

Abstract : Recently there has been considerable interest in the potential for using single crystal alpha AlPO4 in a variety of acoustic wave applications. This interest was prompted by the possibility of obtaining simultaneously in one material, the properties of temperature stability, low acoustic loss, and high piezoelectric coupling. The poor quality and general lack of large alpha AlPO4 single crystals has precluded the evaluation and testing of this material in the desired prototype devices. This situation has motivated development of a noval synthesis technique for attaining such crystals. This paper describes a unique modification (patent pending) of the conventional hydrothermal growth method which yields large (3cm), high-optical-quality single crystals. The method permits continuous visual observation of the pressurized crystal growth process thus permitting close control of real-time nucleation and growth kinetics. The optimum conditions for attaining high quality crystals such as temperature-ramp rates, reagent concentration and purity, system design, and ampoule configuration are presented.