Piezoelectric glass-ceramic for high-temperature applications

Abstract

We report on a non-ferroelectric, piezoelectric polar glass-ceramic specifically targeted for high-temperature sensor use (T > 300 °C). Potential applications include accelerometers for turbine engines and in-cylinder pressure sensors for diesel engines. Choice of an alkali-free, Sr-fresnoite (Sr2TiSi2O8) + added SiO2 bulk composition led to desirably high electrical resistivity while maintaining good piezoelectric sensitivity. Piezoelectric properties are highly competitive with existing high-temperature single crystals and ceramics, consisting of d33 = 10, d31 = 1.5, and d15 = 34 (pC/N). Support for the high value of the shear mode d15 coefficient comes from both direct measurement as well as consideration of the expected variation in effective d33 due to deviation in perfect (001) crystalline alignment, as demonstrated in this system by Wisniewski et al. (2012). Due to the low dielectric permittivity in this system (ε33T/ε0 = 11.5; ε11T/ε0 = 16.5, both at 1 kHz), the voltage coefficients are quite high: g33 = 103, g31 = 15, and g15 = 233 (×10−3 V m/N). The room-temperature pyroelectric coefficient p3 of +8 μC/m2/°C is followed by a hysteretic peak, though repeatable, near 175 °C, attaining −70 μC/m2/°C, but by 250 °C, p3 has returned to low levels and passes through zero around 275 °C. Of crucial particular importance for high-temperature applications is high electrical resistivity, well exemplified by this material, with ρ ~ 1012 Ω-cm at 300 °C and 106 at 850 °C; higher levels of resistivity can be obtained through use of raw materials with lower levels of alkali contaminants. The combination of high electrical resistivity coupled with good piezoelectric sensitivity and the lack of a Curie temperature, with its associated aging effects, makes Sr-fresnoite glass-ceramics a realistic contender in the technically-challenging field of high-temperature piezoelectric materials.