Piezoelectric unimorphs and bimorphs were fabricated by utilizing (100) plane Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3(PZNT91/09) single-crystal plates with giant k31 over 80%, which appeared in the case of a phase with low crystal symmetry. The electromechanical coupling factors on bending mode (k b ) were 64.7% (PZNT91/09 single crystals) and 20.6% (PZT ceramics) in the case of unimorphs. The values of k b in bimorphs were 69.8% (PZNT91/09 single crystals) and 31.2% (PZT ceramics), respectively. Furthermore, the PZNT91/09 single-crystal bimorph showed the superior piezoelectric properties such as three times larger impedance ratio on the resonant and the anti-resonant frequencies. The single-crystal devices possessed the excellent displacement characteristics in comparison with the ones of the PZT ceramic devices.