Effect of local strain fields on the structural, Neel transition temperature and long range ferroelectric ordering in rare earth substituted Bi_(0.9)R_(0.1)FeO_3 multiferroic ceramics (where, R = Gd~(3+), Tb~(3+), Dy~(3+))

摘要

X-ray diffraction analysis of BiFeO_3 (BFO) and rare earth (R) substituted BiFeO_3 (BRFO) ceramics revealed the pervoskite phase formation. Raman scattering measurements elucidated the weakening of Bi-O covalent bond and destabilization in FeO_6 octahedral chains in BRFO ceramics. A variation in Fe-O bond length and modulation in FeO_6 local environment were evidenced from UV-visible spectroscopic studies. A weak ferro-magnetism along with high coercivity (H_C) values was observed for BRFO ceramics. Heat flow measurements revealed a reduction in Neel transition temperature (T_N) and a slight increase in Curie transition temperature (T_C). The suppression of long range ferroelectric ordering in BRFO ceramics were probed from the nature of endotherm corresponding to T_C. The variation and nature of phase transitions in BRFO ceramics were explained based on a structural model by considering the local strain fields created by ordered oxygen displacements due to A-site cation disorder and size variance effects.