Quartz homeotypic gallium-orthophosphate-a new high tech piezoelectric material

In the recent years, the crystallographic and physical properties of quartz homeotypic gallium orthophosphate (GaPO₄) have been studied and are summarized. Compared with quartz, these crystals show higher piezoelectric coefficients and therefore a larger electromechanical coupling. Its alpha-quartz-structure is stable up to 1206 K, where a transition to a cristobalite-like structure occurs. An alpha-beta transition does not occur, because the transition temperature would be theoretically near the melting temperature of 1943 K. Nevertheless there exist temperature compensated cuts for BAW and for SAW applications. Beside the higher coupling, the most outstanding property of these crystals is their thermal stability and the very small temperature dependency of the most important physical properties. This makes GaPO₄ the leading material for sensors and high temperature applications. Due to a breakthrough in the growth technology of these crystals, arising from epitaxial growth on quartz seeds, it should be possible to produce this material on an industrial scale within the next years