Effect of poling direction on microhardness and indentation fracture toughness in PMN-0.28PT and PMN-0.32PT single crystals

Abstract

The relaxor ferroelectric Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) has been considered to be a potential choice for high performance actuators and sensors owing to their ultrahigh electromechanical properties. Their devices are often subjected to contact loading which may nucleate surface cracks leading to catastrophic failure. Therefore, in order to understand the deformation and fracture behavior, Vickers micro-indentation experiments are performed on [001] oriented poled PMN-0.28PT and PMN-0.32PT single crystals along parallel and perpendicular to the poling direction. Results show that the hardness, H is primarily governed by the orientation of domains with respect to the loading direction. The finite element simulations demonstrated that H increases with rise in piezoelectric coupling coefficient, d33. Further, the length of crack parallel to poling direction is found to be larger than that of perpendicular to poling direction when indentation load is perpendicular to the poling direction. This behavior is in contrast to the trend reported for Pb(ZrxTi1−x)O3 (PZT), BaTiO3, and lead-free piezoelectric materials in the past. The Switching spectroscopy piezoresponse force microscopy (SS-PFM) performed along the cracks shows different patterns of d33* for crack parallel and perpendicular to the poling direction. Motivated from the observed trend in d33*, the mechanism of crack propagation is presented and the reasons for anisotropy in KIC is also explained. © 2023 Acta Materialia Inc.