Microindentation response of relaxor ferroelectric PMN-0.32PT single crystal

Abstract

The relaxor ferroelectric 0.68Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 (PMN-0.32PT) which lies near the morphotropic phase boundary (MPB) composition has gained attention in the recent past due to its excellent electromechanical properties. The devices made of these materials are often subjected to contact forces which may lead to domain switching/phase-transformation resulting in poor electromechanical properties and sub-standard performance. This has encouraged researchers to understand their deformation behavior under contact loading such as indentation. The indentation experiments on other relaxor ferroelectric materials reported the indentation size effect (ISE) in the hardness, though mechanistic reasons for this behavior are not well understood. In addition, the ISE in the relaxor ferroelectric PMN-0.32PT has not been investigated in detail till now. Therefore, Vickers micro-indentation experiments are performed on [001] poled PMN-0.32PT single crystals. The results show that these crystals exhibit a strong ISE. Further, the load-independent hardness of these crystals is found to be 4.85 ± 0.05 GPa which is in agreement with the previously reported values. The XRD analysis performed on indented surface suggests indentation induced phase transformation which is further confirmed by Raman spectroscopy. It is found that the ISE in PMN-0.32PT single crystals can be satisfactorily described by proportional specimen resistance (PSR) model, but not by modified PSR model. Thus, it is concluded that the ISE in poled PMN-0.32PT single crystals can be attributed to the combined effect of resistance offered by the specimen to indenter penetration, the interface friction, and the polarization-rotation induced phase transition below the indenter.