Measurement of independent piezoelectric constants of a lanthanumgallium silicate family crystals by X-ray diffraction method

Independent piezoelectric strain coefficients d₁₁ and d₁₄ in disordered La₃Ga_5.3Ta_0.5Al_0.2O₁₄ (LGTA) and ordered Ca₃TaGa₃Si₂O₁₄ (CTGS) crystals of the langasite family were measured by high-resolution X-ray diffraction (HRXRD) under external electric field application which causes changes in the interplanar spacing because of the reverse piezoelectric effect. The experiment showed that the piezoelectric strain coefficients can be precisely determined by measuring changes in the interplanar spacing using the optical scheme of a triple-axis X-ray diffractometer. The measured independent piezoelectric strain coefficients d₁₁ and d₁₄ for LGTA and CTGS crystals were d_11(LGTA)=6.455·10^-12 C/N, d_14(LGTA)=-5.117·10^-12 C/N; d_11(CTGS)=3.330·10^-12 C/N, d_14(CTGS)=-15.835·10^-12 C/N.