Piezoelectric properties at high temperature in $\alpha$-quartz materials

The performances of resonators made of $\alpha $-quartz and GaPO$_{4}$ are compared based on piezoelectric measurements up to 850°C. Up to now, no explanation was available for the observed decrease in piezoelectric performances well below the phase transition temperature in these materials. Total neutron scattering measurements were used to determine the instantaneous structural disorder as a function of temperature. The losses of piezoelectric properties measured above 700$^{\circ}$C for GaPO$_{4}$ can thus be correlated to an important degree of structural disorder, which is evaluated by various angular distributions. The distribution of the intertetrahedral O-O-O bridging angle values becomes very wide for this material between 700 and 800$^{\circ}$C. The relative movement of the tetrahedra can provide an explanation for the observed piezoelectric losses well before the phase transition