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 Sr x Ba 1−x Nb 2 O 6 (x = 0.35, 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-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-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 Sr x Ba 1−x Nb 2 O 6 and provide a deeper insight into the origins of the materials dielectric properties.

Composition and morphology tuning during hydrothermal synthesis of SrxBa1−xNb2O6tetragonal tungsten bronzes studied byin situX-ray diffraction

“…In addition SBN has good pyroelectric 11,12 and photorefractive properties 13 . Moreover, reduced SBN (SrxBa1−xNb2O6−δ) is reported to have promising thermoelectric properties 14 and filled SBN (SrxBa1.2-xNb2O6) is reported to show low temperature superconductivity 15 .The crystal structure of SBN consists of corner-sharing NbO6 octahedra forming triangular C-sites (empty in SBN), square A1sites and pentagonal A2-sites 6,16 filled with a total of 5 alkaline earth atoms, and 1 vacancy, as shown in Figure 1. The average structure is described by the P4bm space group, but a better understanding of the link between order/disorder, polarization and incommensurate tilting of NbO6 octahedra in the structure is still being addressed 16,17 .…”

“…Moreover, reduced SBN (SrxBa1−xNb2O6−δ) is reported to have promising thermoelectric properties 14 and filled SBN (SrxBa1.2-xNb2O6) is reported to show low temperature superconductivity 15 .The crystal structure of SBN consists of corner-sharing NbO6 octahedra forming triangular C-sites (empty in SBN), square A1sites and pentagonal A2-sites 6,16 filled with a total of 5 alkaline earth atoms, and 1 vacancy, as shown in Figure 1. The average structure is described by the P4bm space group, but a better understanding of the link between order/disorder, polarization and incommensurate tilting of NbO6 octahedra in the structure is still being addressed 16,17 . The three species, ((5-x)*Sr 2+ , x*Ba 2+ and one vacancy) are distributed on a total of 6 sites per unit cell (2 A1-and 4 A2-sites), and one X-ray diffraction experiment is not sufficient to determine the occupancy of Ba 2+ , Sr 2+ and the vacancy on the two sites due to parameter correlations 18 .…”

Local structure of Mott insulating iron oxychalcogenides La2O2Fe2OM2(M=Karki1, Alfailakawi2, Frandsen3 et al. 2021Phys. Rev. B

“…Having obtained a confirmation of the global lattice symmetry for our samples, we then investigated the local symmetry [30,34,[44][45][46][47]. The local structure data of La 2 O 2 Fe 2 OM 2 (M = S, Se) were analyzed by using the PDF refinement program PDFGUI [37] to determine the lattice parameters, scale factor, atomic positions, and the thermal parameters.…”

Total scattering and the pair distribution function in crystallography

“…broadened) instrumental resolution. A Q max 23Å −1 and Q-resolution of around 2.25% [62] on D4c is sufficient for the majority of liquid and glass diffraction patterns, but it can be limiting for highly crystalline materials. The Q resolution broadens Bragg peaks, giving rise to less well resolved Rietveld refinements, and suppresses the intensities of high-r features in the PDF.…”