High temperature ReCOB piezocrystals: Recent developments

Piezoelectric sensors for high temperature applications have attracted attention due to their simplistic structure, fast response time and ease of integration. In this article, oxyborate ReCa4O(BO3)3 (Re: rare earth element; abbreviated as ReCOB) piezoelectric crystals were surveyed for their potential use in high temperature sensing applications. In contrast to quartz and GaPO4 crystals, no phase transformation(s) are observed prior to their melting points, being in the order of ∼1500°C. The electrical resistivity, dielectric, piezoelectric properties and resonance-impedance characteristics were studied as a function of temperature over the range of Room Temperature (RT) to 950°C. The resistivity of ReCOB was found to be ∼2×108Ohmcm at 800°C, two orders higher than langasite, another widely studied crystal system. The electromechanical coupling factors k26 and piezoelectric coefficients d26 were found to be >20% and >10pC/N, respectively, with the variation being