Size effect of mechanical behavior for lead-free (Na0.82K0.18)0.5Bi0.5TiO3 nanofibers by nanoindentation

The nanoscale mechanical behaviors of (Na0.82K0.18)0.5Bi0.5TiO3 (NKBT) piezoelectric nanofibers and thin film were investigated by nanoindentation technique in detail. In comparison with the reduced modulus (158.2 GPa) and hardness (7.3 GPa) of NKBT thin film, the reduced modulus and hardness are 107.6 GPa and 4.9 GPa for the nanofibers, and they decrease by 31.9% and 32.8%. The size effect of the mechanical behavior was obviously observed for the nanofibers, and the mechanism is discussed in conjunction with high surface-to-volume ratio. Indentation depth-dependent reduced modulus and hardness properties were also observed for the nanofibers, and they may be attributed to the strain gradient effect during nanoindentation.