The method to distinguish two types of monoclinic phases (M-A and M-B) in perovskite crystals by polarized light microscopy was developed. The MA-type monoclinic phase was observed in xPb(In1/2Nb1/2)O-3-yPb(Mg1/3Nb2/3)O-3-zPbTiO(3) ternary crystal by polarized light microscopy at room temperature. The phase transition of these monoclinic phases under dc electric field along [1 1 0](cub) direction was investigated in real time. Two dielectric peaks were found in ferroelectric phases of the as-grown ternary single crystals near the morphotropic phase boundary (MPB) with increasing temperature, which indicate the phase transition of monoclinic M-A -> orthorhombic (O) -> tetragonal (T). (C) 2010 Elsevier B.V. All rights reserved.