Short- and medium-range structure of multiferroic Pb(Fe_1/2Nb_1/2)O₃ studied using neutron total scattering analysis

Abstract

We performed neutron total scattering analysis on multiferroic Pb(Fe_1/2Nb_1/2)O₃ (PFN) from 300 K to 75 K and present the evolution of short- and medium-range atomic structures across the antiferromagnetic transition, T_N=143 K. Over the whole temperature range, off-center displacement of Fe/Nb ions was not significant and Fe/Nb-O bond-length distribution exhibits little temperature dependence. In contrast, Pb-O bond length showed a rather distinct distribution at high and low temperatures. Using a comparison between crystallographic modeling and total scattering pair distribution function analysis we propose that a displacement of the Pb ion against the Fe/Nb ions is an important low-temperature structural feature. In addition, we present evidence for a static broadening at T=150 K due to the antiferromagnetic ordering of B-site Fe ions. Overall, we found that Fe/Nb ions play a role in the multiferroic properties of PFN by influencing off-centering behavior of the Pb ion with decreasing temperature.