Temperature dependence of electrical resistivity, dielectric and piezoelectric properties of Ca3TaGa3-xAlxSi2O14 single crystals as a function of Al content

High quality colorless Ca3TaGa3-xAlxSi2O14 (CTGAS) single crystals are successfully grown by the Czochralski technique within the full solid solution range. The influence of Al content on the electrical resistivity, dielectric and piezoelectric properties is systematically investigated for the first time at room temperature, as well as a function of temperature up to 700 degrees C. With the increase of Al content the resistivity, the electromechanical coupling factor k(12) and the piezoelectric coefficient d(11) increase, while the dielectric permittivity epsilon(T)(11)/epsilon(0) decreases. CTGAS single crystals exhibit a very low dielectric loss (<1%) till 550 degrees C, and the electrical resistivity is over 10(10) Omega cm at 400 degrees C for all samples, i.e. more than two orders of magnitude higher than that of the considered material La3Ta0.5Ga5.5-xAlxO14. Present results indicate that, among the langasite family, Ca3TaGa3-xAlxSi2O14 is at present the most promising crystal for high temperature sensor applications, since it exhibits the highest resistivity and a good piezoelectric response. (C) 2016 Elsevier B.V. All rights reserved.