Local structure of relaxor ferroelectric SrxBa1−xNb2O6 from a pair distribution function analysis

Abstract

Pair distribution function analysis of neutron-scattering data and of ab initio molecular dynamics results have been employed to study short-range structural correlations and their temperature dependence in a heavily disordered dielectric material ${\mathrm{Sr}}_{x}{\mathrm{Ba}}_{1\ensuremath{-}x}{\mathrm{Nb}}_{2}{\mathrm{O}}_{6}\phantom{\rule{4pt}{0ex}}(x=0.35,\phantom{\rule{0.28em}{0ex}}0.5$, and 0.61). Intrinsic disorder caused by a partial occupation of the cationic sites by differently sized Sr and Ba atoms and their vacancies introduces important local strains to the structure and directly influences the Nb-${\mathrm{O}}_{6}$ octahedra tilting. The resulting complex system of tilts is found to be both temperature and Sr-doping sensitive with the biggest tilt magnitudes reached at low temperatures and high strontium contents, where ferroelectric relaxor behavior appears. We find evidence for two Nb-${\mathrm{O}}_{6}$ subsystems with different variations of niobium-oxygen bond lengths, distinct dynamics, and disparate levels of deviation from macroscopic polarization direction. These findings establish a detailed picture of the local structure of ${\mathrm{Sr}}_{x}{\mathrm{Ba}}_{1\ensuremath{-}x}{\mathrm{Nb}}_{2}{\mathrm{O}}_{6}$ and provide a deeper insight into the origins of the materials dielectric properties.