Quantitative analysis of the direct piezoelectric response of bismuth ferrite films by scanning probe microscopy

Polarisation domain structure is a microstructure specific to ferroelectrics and plays a role in their various fascinating characteristics. The piezoelectric properties of ferroelectrics are influenced by the domain wall contribution. This study provides a direct observation of the contribution of domain walls to the direct piezoelectric response of bismuth ferrite (BiFeO₃) films, which have been widely studied as lead-free piezoelectrics. To achieve this purpose, we developed a scanning probe microscopy-based measurement technique, termed direct piezoelectric response microscopy (DPRM), to observe the domain structure of BiFeO₃ films via the direct piezoelectric response. Quantitative analysis of the direct piezoelectric response obtained by DPRM, detailed analysis of the domain structure by conventional piezoelectric force microscopy, and microscopic characterisation of the direct piezoelectric properties of BiFeO₃ films with different domain structures revealed that their direct piezoelectric response is enhanced by the walls between the domains of spontaneous polarisation in the same out-of-plane direction.