Phase transitions and piezoelectricity enhancement around MC → O phase transition in PMN-0.34PT single crystals

Phase transitions of Pb(Mg1/3Nb2/3)O-3-0.34PbTiO(3) (PMN-0.34 PT) have been studied by using dielectric constant variations, polarization-electric field hysteresis loops, and polarizing light microscopy (PLM). Even without the assistance of electric field, orthorhombic (O) phase exists in the [001](C)-oriented PMN-0.34 PT single crystals during the heating process, which is confirmed by the polarizer/analyzer extinction angle from full-angle in situ PLM observation combined with the grayscale image analysis. The phase transition sequence is monoclinic (M-C) -> O -> M-C -> tetragonal (T) -> cubic (C), which is different from the commonly accepted M-C -> T -> C sequence. The existence of the O phase accompanies with much enhanced dielectric and piezoelectric performance, which indicates a new mechanism to produce large piezoelectricity in PMN-PT single crystals. (C) 2020 Elsevier B.V. All rights reserved.