Electro-acoustical constants and Rayleigh SAW propagation characteristics of rare-earth calcium oxoborate single crystals

Electro-acoustical constants (eij T , sij E , dij) of the rare- earth calcium oxoborate RCa4O(BO3)3 (R = La, Gd, Y; RCOB) piezoelectric single crystals, which belong to the monoclinic structure with point group m, were evaluated. Their electro- acoustical constants were systematically compared to the ionic radius of the R-site ions. The piezoelectric constants d11, d12, d13, d31, d32 and d33 hardly changed with the increasing R-site ionic radius. It was confirmed that the 1/(ρ sii E ) terms, which consist of diagonal components of elastic compliances (sii E : i = 1-6) and the RCOB crystal density ρ, were closely related to the measured SAW velocities. The Rayleigh SAW velocities for the fundamental X-, Y- and Z-cuts were theoretically calculated in their crystals, which showed a good agreement with the measured values in all the fundamental cuts of their crystals. In common among their crystals, symmetrical propagation profiles were obtained on the X- and Z-cuts, on the other hand, the Y-cut did not show any symmetrical propagation ones. The Euler angles Ψ with minimum Rayleigh SAW velocities on their Y-cuts were larger than 90 o . These results in their Y-cuts were attributed to