Low symmetry mono-domain Pb[(Zn/sub 1/3/Nb/sub 2/3/)/sub 0.91/T1/sub 0.09/]O/sub 3/ single crystal with giant electromechanical coupling factor of k/sub 31/ mode

Frequency responses of impedance to 500 kHz in Pb[(Zn/sub 1/3/Nb/sub 2/3/)/sub 0.91/Ti/sub 0.09/]O/sub 3/ (PZNT91/09) single-crystal plates (13/sup L//spl times/4/sup W//spl times/0.36/sup T/ mm) were analyzed on the two kinds of the length extensional vibration modes of k/sub 31/ (13/sup L/ mm) and k/sub 32/ (4/sup 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 k/sub 31/ over 80% has only in the case of the low fc on k/sub 31/ mode and the high fc on k/sub 32/ mode, which are caused by the anisotropy of the crystal symmetry. It was thought that the crystal structure with the giant k/sub 31/ was transformed into a new phase such as monoclinic phase different from rhombohedral and tetragonal phases. Therefore, the giant k/sub 31/ appeared in the case of a low symmetry phase, which can be realized mono-domain structure in the single-crystal plates.