Microhardness and fracture toughness of 〈1 1 1〉-oriented Pb(Zn1/3Nb2/3)O3-PbTiO3 single crystal

Novel relaxor ferroelectric single crystal (1−x)Pb(Zn1/3Nb2/3)O3-xPbTiO3 (PZNT) was grown by vertical Bridgman method, the mechanical properties of the (1 1 1) face were systematically researched using microindentation technique. It was found that the Vickers' microhardness Hv was as a function of the applied load. In the range of 0.1-3 kg, Hv was decreased from 4.03 to 3.26 GPa. The dependence of Hv on applied load could be explained on the basis of Kick's law, and the Meyer index n was determined to be 1.88. In-plane crack anisotropy behavior was observed on the wafer, the crack length in the direction parallel to domain wall was longer than that perpendicular to it, therefore, the (1 1 1) PZNT crystal displayed fracture toughness Kc anisotropy accordingly. The crack types (radial-median and Palmqvist systems) parallel and perpendicular to the domain wall in the 0.1-3 kg load range were classified.