Resistivity and piezoelectric properties of Ca3TaGa1.5Al1.5Si2O14 single crystals for high temperature sensors

Abstract

High quality colorless Ca₃TaGa_1.5Al_1.5Si₂O₁₄ (CTGAS) single crystals are successfully grown by the Czochralski method for high temperature (over 200 °C) sensor applications. The full set of properties, including thermal expansion, resistivity, dielectric, elastic and piezoelectric constants, is characterized as a function of temperature for the first time. The thermal expansion of CTGAS is nearly isotropic, which is beneficial to prevent stress and cracking after growth and in various temperature applications. The variation of the dielectric permittivities is about 4% between room temperature and 650 °C, while the dielectric loss is less than 2%. In the same temperature range, the piezoelectric coefficient d₁₁ increases from 4.15 to 5.03 pC N⁻¹ (about 21%). The average temperature coefficient frequency of the (XYt) −30° plate is as small as −15 ppm K⁻¹. Furthermore, the resistivity of CTGAS grown under an low oxygen partial pressure atmosphere is as high as ∼4 × 10¹⁰ Ω cm at 400 °C, which is more than two orders of magnitude better than that of the reference candidate La₃Ta_0.5Ga_5.1Al_0.4O₁₄. Altogether, CTGAS exhibits excellent electric and piezoelectric properties at elevated temperatures, and therefore is a promising candidate for high temperature sensor applications.