New results on the thermal sensitivity of bulk and surface modes of gallium orthophosphate GaPO/sub 4/

Gallium orthophosphate (GaPO/sub 4/) is a piezoelectric crystal with the same class of symmetry as quartz, exhibiting higher electromechanical coupling factors for both bulk and surface waves. In this paper the results obtained for velocity measurements of bulk modes of GaPO/sub 4/ at low temperatures (from 4 K to 273 K) using the pulse-echo technique are presented. A set of elastic constants is derived together with their temperature coefficients, and a comparison is made with recent values proposed by Krempl et al. GaPO/sub 4/ already appears as an acoustic material with an exceptional temperature stability, superior to quartz. In parallel, results on the thermal sensitivity of Rayleigh surface waves on GaPO/sub 4/ are presented. A temperature-compensated cut at 75/spl deg/C has been found on a Z-cut plate exhibiting a parabolic frequency-temperature dependance with a 2nd order temperature coefficient of about 25/spl times/10/sup -9/ K/sup -2/, better than the conventional (ST, X) SAW cut of quartz.