Anomalous atomic displacement parameters and local dynamics in the Curie range of a Pb-free relaxor ferroelectric system (Bi_(1-x)Ba_x)(Fe_(1-x)Ti_x)O_3(0.36 ≤ x ≤ 0.50)

摘要

We report here the relaxor ferroelectric (RFE) behaviour in a multiferroic solid solution system, (Bi1-xBax)(Fe1-xTix)O-3, at a critical disorder level of x(C) similar to 0.35 in BiFeO3 and 0.65 (i.e., 1-x(C) = 0.35) in BaTiO3 similar to the 1:2 ratio of Mg2+ and Nb5+ in the canonical RFE Pb(Mg1/3Nb2/3)O-3. This Pb-free system, like canonical Pb-based RFEs, does not exhibit macroscopic symmetry breaking and shows only the signatures of ergodicity breaking at Vogel-Fulcher freezing temperature (T-VF). The atomic displacement parameters (ADPs) of Fe3+/Ti4+ and O2-, obtained using high wave vector (Q) and high-resolution synchrotron x-ray diffraction data as a function of temperature, show anomalous diffuse peaks in the Curie range. It is shown that the diffuse peak in ADPs is due to softening of the vibrational frequencies of the B-O chain (B = Fe3+/Ti4+ and O = O2-) below the Burns temperature (T-B) followed by hardening below the characteristic temperature (T'(m)), which corresponds to a peak in the dielectric permittivity (epsilon'). Published by AIP Publishing.