Electric field induced nanoscale polarization switching and piezoresponse in Sm and Mn co-doped BiFeO₃ multiferroic ceramics by using piezoresponse force microscopy

Samarium (5%Sm) and manganese (0.5%Mn) co-doped BiFeO₃ (B5SF0.5MO) polycrystalline multiferroic ceramics were prepared by solid-state-reaction to study the morphology, local polarization switching and piezoresponse, using atomic force microscopy (AFM) and piezoresponse force microscopy (PFM). Room temperature x-ray diffraction (XRD) and micro-Raman spectra reveal that samarium and manganese co-doping retains the parental rhombohedral R3c structure of BiFeO₃ (BFO). The out-of-plane (OP) PFM phase images show domains with oppositely oriented polarizations which are distinguished as domains with downward and upward polarizations with respect to the cantilever direction. Polarization switching occurs in the poled sample by locally poling the sample at negative and positive biases. Following the domain switching mechanism in BFO, it was found that 109° domain switching occurred besides the growth of 180° domains upon application of an electric field. The clockwise phase hysteresis implies the Debye model of piezoelectric relaxation effect due to defects that are both elastic and electric dipoles. The negative self-polarization in these samples is supposed to be the result of built-in internal bias field generated from excess electrons and charge defects like oxygen vacancies. The Saturated localized in-field hysteresis phase and amplitude loops from 180° domains suggest the existence of well-defined polarization along the field direction and suggests that Sm and Mn co-doped BFO can be a potential material for nanoscale piezoelectric applications.