Multiferroic bismuth ferrite: Perturbed angular correlation studies on its ferroic α-β phase transition

Marschick G, Schell J, Stöger B, Gonçalves J N, Karabasov M O, Zyabkin D, Welker A, Escobar M, Gaertner D, Efe I, Santos R A, Laulainen J E M, Lupascu D C

Abstract

Work of numerous research groups has shown different outcomes of studies of the transition from theferroelectric α-phase to the high temperature β-phase of the multiferroic, magnetoelectric perovskite BismuthFerrite (BiFeO 3 or BFO). Using the perturbed angular correlation (PAC) method with 111m Cd as the probenucleus, the α to β phase transition was characterized. The phase transition temperature, the change of thecrystal structure, and its parameters were supervised with measurements at different temperatures using a sixdetector PAC setup to observe the γ -γ decay of the 111m Cd probe nucleus. The temperature dependence of thehyperfine parameters shows a change in coordination of the probe ion, which substitutes for the bismuth site,forecasting the phase transition to β-BFO by either increasing disorder or formation of a polytype transitionstructure. A visible drop of the quadrupole frequency ω 0 at a temperature of about T c ≈ 820 ◦ C indicates the α-βphase transition. For a given crystal symmetry, the DFT-calculations yield a specific local symmetry and electricfield gradient value of the probe ion. The Pbnm (β-BFO) crystal symmetry yields calculated local electric fieldgradients, which very well match our experimental results. The assumption of other crystal symmetries resultsin significantly different computed local environments not corresponding to the experiment.