Correlated rattling-ion origins of dielectric properties in reentrant dipole glasses BaTiO3-BiScO3

Abstract

The local structure of the pseudo-cubic solid solution 0.6BaTiO3-0.4BiScO3, which exhibits reentrant dipole-glass behavior, has been determined using the Reverse Monte Carlo method to simultaneously fit (1) neutron and X-ray total scattering data (including the corresponding real-space pair-distribution functions), (2) Bi and Sc extended X-ray absorption fine structure, and (3) patterns of diffuse scattering in electron diffraction. These structural refinements revealed the multi-site probability density distributions for both Bi (14-sites) and Ti (8 sites), whereas Ba and Sc featured normal unimodal distributions. Bi atoms are displaced along both the 〈111〉 and 〈100〉 directions, while Ti atoms are shifted along 〈111〉. Correlated dynamic hopping of Bi and Ti over their corresponding split sites combined with chemical disorder is proposed as the origin of the strong frequency dispersion observed in dielectric measurements. The existence of split sites also explains the reentrant dipole-glass behavior reported for this system.