Elastic, Inelastic and Fracture Characteristics of Relaxor Ferroelectric Materials via Nanoindentation

The unique non-uniform polar nanoregions and complex phase structure near morphotropic phase boundaries (MPBs) in relaxor ferroelectric materials lead to rich microstructure changes (domain transition, phase transition) under external field stimulation. This not only results in the material with extremely high electromechanical properties, but also greatly affects their mechanical properties and stability.

This study investigated the fundamental mechanical properties of the rhombohedral phase (R-phase) and tetragonal phase (T-phase) structures of the relaxor ferroelectric single crystal PMN-PT material using the nanoindentation with different shapes of indenters.

The basic mechanical properties of the material were measured by nanoindentation, and the fracture caused by indentation was analyzed by scanning electron microscopy.

The elastic modulus of R-phase relaxed ferroelectric materials showed a significant dependence on the indentation depth, and the hardness of different phases (R, T-phase) materials all show obvious indentation size effects (ISE). Under the loading of the spherical indenter, both R and T phase materials exhibited a pop-in phenomenon caused by the transition from elastic to inelastic. Under the loading of the Berkovich indenter, the R and T phase materials showed different fracture characteristics of crack propagation response with the increase of the indentation depth.

The result demonstrate that the mechanical properties of relaxor ferroelectric materials are significantly related to their phase structure, providing guidance for the design of load bearing and material selection in the practical application of related ferroelectric devices.