Dislocation influence on nanoscale mechanical and ferroelectric behavior of ferroelectric barium titanate.

摘要

Plastic behavior during loading of ferroelectric materials is commonly explained by domain activities, e.g., domain nucleation and domain switching. However, we show that, in this dissertation, plastic behavior of ferroelectrics during nanoindentation is a cooperative event of dislocation activity and domain switching. Studies are conducted on ferroelectric BaTiO3 single crystal by employing an advanced nanoscale characterization technique based on nanoindentation and atomic force microscopy (AFM). Elastic modulus and hardness of individual domains are measured by nanoindentations with a Berkovich indenter. A conical indenter is chosen to generate radially symmetrical stress fields. Following nanoindentations, the residual impressions are imaged by AFM and PFM to characterize the indentation-induced plastic and cracking behavior on the surface. On one hand, dislocation activities are deduced from anisotropic material pileups and rosette screw arms around residual impression. Significantly shorter cracks in the c-domain under the same indentation load suggest a higher apparent fracture toughness of the c-domain, which is estimated to be approximately 3 times higher than that of a-domain. On the other hand, PFM images reveal different domain switching patterns around residual impressions in a- and c-domains. Both indentation-induced cracks and domain switching are believed to be assisted by dislocation pile-ups against the sessile dislocation created at the intersection of two neighboring {110} 45 planes. Finally, the cause of different apparent fracture toughness between a- and c-domains is discussed based on dislocation activities and domain switching.