Role of local disorder in the dielectric response of BaTaO₂N

Short-range structural disorder of the high-κ dielectric BaTaO₂N is revealed by the analysis of the extended x-ray-absorption fine-structure (EXAFS) spectroscopy measured at the Ta L_III edge. Although previous neutron, x-ray, and electron diffraction studies have shown BaTaO₂N to crystallize in a centrosymmetric, cubic structure, these EXAFS spectra show a wide distribution of first shell Ta-(O,N) distances with further implications to nonuniformity of the existing octahedral distortions. A distortion model based upon a density functional theory energy minimization for a 4×4×4 supercell of BaTaO₂N was used to successfully interpret these EXAFS data. We find that structural distortions with very short correlation lengths exist in this material and that these distortions are consistent with the large dielectric permitivity of BaTaO₂N.