  Electric field dependent mechanical properties of relaxor ferroelectric
material Pb(Mn1/3Nb2/3)O3-PbTiO3 are investigated with the nanoindentation
technique. Giant electric-field-tunable apparent elastic modulus (up to -39%),
hardness (-9% to 20%) and energy dissipation (up to -13%) are reported. Based
on experimental data, a characterization method of electromechanical coupled
nanoindentation is proposed. In this method, an electric field tunable scaling
relationship among elastic modulus, hardness and indentation work for
ferroelectric materials can be determined. In addition, this method can be used
to obtain the electric-field-dependent elastic modulus and hardness, and avoid
the estimate of contact area in the Oliver-Pharr method. Finally, the different
effects on elastic modulus between positive and negative electric fields can be
explained by the flexoelectric effect.
