Low symmetry mono-domain Pb[(Zn13/Nb23/)0.91T10.09]O3 single crystal with giant electromechanical coupling factor of k31 mode

Frequency responses of impedance to 500 kHz in Pb[(Zn₁3/Nb₂3/)_0.91Ti_0.09]O₃ (PZNT91/09) single-crystal plates (13^L×4^W×0.36^T mm) were analyzed on the two kinds of the length extensional vibration modes of k₃₁ (13^L mm) and k₃₂ (4^W mm). It was found that there were two (low and high) frequency constants (fc) of 520 kHz-m and 830 kHz-m on these modes. The response with the giant k₃₁ over 80% has only in the case of the low fc on k₃₁ mode and the high fc on k₃₂ mode, which are caused by the anisotropy of the crystal symmetry. It was thought that the crystal structure with the giant k₃₁ was transformed into a new phase such as monoclinic phase different from rhombohedral and tetragonal phases. Therefore, the giant k₃₁ appeared in the case of a low symmetry phase, which can be realized mono-domain structure in the single-crystal plates.