Full tensor properties of [111]_C poled (Na, K)(Nb,Ta)O₃ lead-free single crystal

Complete sets of elastic, piezoelectric and dielectric constants of [111]_C poled (Na,K)(Nb, Ta)O₃ single crystal have been measured. The results show that the crystal with “3O” domain structure exhibits high shear but low longitudinal piezoelectric properties (d15=140 pC/N, k₁₅=0.569, d₃₃=64 pC/N and k₃₃=0.450), which is similar to the “1O” single domain state, but different from the “4O” multi-domain state. The orientation-dependent longitudinal properties, e.g., d₃₃^⋆, ε₃₃^⋆, s₃₃^⋆ and k₃₃^⋆ in the (01¯1)_C plane have been calculated. The maximum piezoelectricity exists at the position of 38° away from [011]_C, which is close to the [111]_C direction. By comparing the measured and calculated parameters, it can be concluded that the piezoelectricity is dominated by the intrinsic contribution while the dielectricity is controlled by the extrinsic contributions.