Deformation and fracture behaviors of [0 1 1]-poled Pb(Zn1/3Nb2/3)O3–7%PbTiO3 single crystals

The deformation, crack initiation and fracture behavior of [0 1 1]-oriented Pb(Zn1/3Nb2/3)O3–7%PbTiO3 (PZN–7%PT) single crystal samples in both unpoled and poled states have been characterized by means of nano- and microindentation as well as three-point bending experiments. It is found that poling has increased both the elastic modulus and hardness of the (0 1 1) surfaces of the crystal, in addition, the critical indentation load for crack initiation is also increased from 0.225 N for unpoled (0 1 1) surface to 0.475 N for the positive polarity surface (which corresponds to the indentation load direction is against the poling direction), and a slight decreasing in the critical indentation load for crack initiation is noted for the negative polarity surface. It is also found that poling has little effects on the apparent fracture toughness of the (0 1 1) surfaces. These results are compared with those of [0 0 1]-oriented crystals [K.Y. Zeng, Y.S. Pang, L. Shen, K.K. Rajan, L.-C. Lim, Mater. Sci. Eng. A 472 (2008) 35]. The observations are interpreted in term of a compressive stress layer induced by poling in the positive polarity surfaces of the [0 1 1]-poled crystal.