Electric field and temperature induced local polarization switching and piezoresponse in Bi_0.88Sm_0.12FeO₃ ceramics for nanoscale applications

The fundamental understanding of polarization switching in ferroelectric materials is very critical for the development of ferroelectric devices. Electric field and temperature induced nanoscale polarization switching has been studied in polycrystalline Bi_0.88Sm_0.12FeO₃ ceramics using piezoresponse force microscopy (PFM). High resolution synchrotron X-ray diffraction, Rietveld refinements and micro-Raman spectra indicate the phase coexistence of rhombohedral R3c and orthorhombic PbZrO₃-like structures at room temperature. Temperature dependent Raman spectra exhibit nonpolar Pnma phase-like vibrational bands at 175 °C. The PFM amplitude and phase images revealed irregular multi-grain and domain boundaries with oppositely oriented polarizations which are 180° apart in-phase. Step-wise application of negative and positive tip biases indicates that the 109° polarization switching is more favorable at low fields due to large electric and activation energies associated with 180° switching. PFM in-plane (IP) and out-of-plane (OP) images at different temperatures show the 180° domain growth up to 150 °C. The drastic change in the in-plane phase contrast at 175 °C indicates the formation of 71° ferroelastic domains affirming the phase transition. Temperature dependent phase and amplitude measurements exhibit typical hysteresis and butterfly loops below the transition temperature signifying ferroelectric-like piezoelectric behavior. The sudden decrease in the amplitude value at 175 °C supports a phase transition to non-polar phase where piezoeresponse would be nearly zero. However, there exist non-zero piezoresponse regions at 200 °C implying that ferroelectric clusters are embedded in nonpolar phase which make the material ferroelectrically active at nanoscale level.