Local Crystal Structure of Antiferroelectric Bi₂Mn_4/3Ni_2/3O₆ in Commensurate and Incommensurate Phases Described by Pair Distribution Function (PDF) and Reverse Monte Carlo (RMC) Modeling.

ABSTRACT: The functional properties of materials can arise from local structural features that are not well determined or described by crystallographic methods based on long-range average structural models. The room temperature (RT) structure of the Bi perovskite Bi₂Mn_4/3Ni_2/3O₆ has previously been modeled as a locally polar structure where polarization is suppressed by a long-range incommensurate antiferroelectric modulation. In this study we investigate the short-range local structure of Bi₂Mn_4/3Ni_2/3O₆, determined through reverse Monte Carlo (RMC) modeling of neutron total scattering data, and compare the results with the long-range incommensurate structure description. While the incommensurate structure has equivalent B site environments for Mn and Ni, the local structure displays a significantly Jahn-Teller distorted environment for Mn³⁺. The local structure displays the rock-salt-type Mn/Ni ordering of the related Bi₂MnNiO₆ high pressure phase, as opposed to Mn/Ni clustering observed in the long-range average incommensurate model. RMC modeling reveals short-range ferroelectric correlations between Bi³⁺ cations, giving rise to polar regions that are quantified for the first time as existing within a distance of approximately 12 Å. These local correlations persist in the commensurate high temperature (HT) phase, where the long-range average structure is nonpolar. The local structure thus provides information about cation ordering and B site structural flexibility that may stabilize Bi³⁺ on the A site of the perovskite structure and reveals the extent of the local polar regions created by this cation.

SUBMITTER: Szczecinski RJ 

PROVIDER: S-EPMC4311938 | biostudies-literature |

REPOSITORIES: biostudies-literature