Determining the Independent Piezoelectric Coefficients Using Laser Interferometric Method

In this work, the laser interferometric method was used to evaluate the piezoelectric coefficients of crystals in trigonal symmetry, such as LiNbO3 (LN) and La ₃ Ga _5.5 Ta _0.5 O ₁₄ (LGT) crystals. Taking advantage of the high sensitivity of Michelson interferometric, when the piezoelectric crystal deformed at the nanoscale under the applied electric field, the interferometric fringe will change correspondingly, thus amplifying the tiny deformation of the piezoelectric crystals. Compared to the traditional impedance method and ultrasonic method, the laser interferometric method could realize direct measurement and confirm the positive or negative sign of piezoelectric coefficients. The independent piezoelectric coefficients were evaluated to be d11=6.9 pC/N, d ₁₄ =5.0 pC/N for trigonal LGT crystal, and d ₂₁ =-22.8 pC/N, d ₃₁ =0.87 pC/N, d ₃₃ =10.2 pC/N, and d ₁₆ =71.2 pC/N for trigonal LN crystal. The laser interferometric method can be applied for determining the independent piezoelectric coefficients for non-centrosymmetric crystal materials.