Local atomic structure deviation from average structure of Na0.5Bi0.5TiO3

Abstract

The crystal structure of sodium bismuth titanate and related compounds is of great interest, as these may form part of a new generation of ferroelectric materials used in a multitude of piezoelectric applications. This work examines the short and long range structure of sodium bismuth titanate in different states of synthesis using X-ray and neutron pair distribution function studies. The average structure of NBT was modeled using the monoclinic Cc space group through a combined structural refinement of X-ray and neutron diffraction data via the Rietveld method. A small box approach was used to model the local structure based on the average structure of the material, as determined from the Rietveld structural refinement, and rule out the presence of local A-site ordering in NBT. A 'box-car fitting' method used to analyze the neutron PDF showed that bond environments change when averaged over different length scales and the calculated bond valence of Bi 3+ , in particular, is different locally from its average value. A model calculated using the Reverse Monte Carlo method allowed the positions of Na + and Bi 3+ to move independently, allowing the determination of their distinctive bonding environments with O 2-. This method revealed that Na + and Bi 3+ have slightly different atomic positions, an effect that may be the origin of the large atomic displacement parameters calculated for the A-site from the * Corresponding Author: email jjones@mse.ufl.edu, telephone 352-846-3788

Dramatic Influence of A-Site Nonstoichiometry on the Electrical Conductivity and Conduction Mechanisms in the Perovskite Oxide Na0.5Bi0.5TiO3

“…[18][19][20][21][22][23][24][25] Our work shows there are two types of NBT based on the level of nonstoichiometry (resistive stoichiometric NBT and conducting Bi-deficient NBT). It's not clear whether the NBT samples used in the structural studies reported in the literature are resistive or conducting and whether or not these two electrically distinct materials have the same crystal structure.…”

“…[5][6][7][8][9][10][11][12][13][14][15][16][17] NBT has a complex crystal structure. [18][19][20][21][22][23][24][25] Early neutron powder diffraction studies proposed NBT to exhibit a rhombohedral (space group R3c) structure at room temperature (RT). 18 Recent high resolution synchrotron powder x-ray diffraction data suggest a monoclinic structure with space group Cc is a better fit.…”

“…19 Furthermore, the average structure determined by neutron powder diffraction and synchrotron powder x-ray diffraction is different from the local structure, as revealed by X-ray and neutron total scattering experiments and pair distribution function (PDF) analysis. 20,21 The local deviations from the average structure occur because of distinctly different displacements of Na and Bi ions 20 and complex in-phase and out-of-phase octahedral tilting. 22 The complexity of the local structure has been directly demonstrated by transmission electron microscopy, 22 which confirms an essentially random distribution of Bi and Na and reveals significant disorder of the octahedral rotations and cation displacements.…”

Polarization Rotation and Monoclinic Distortion in Ferroelectric (Bi0.5Na0.5)TiO3–BaTiO3 Single Crystals under Electric Fields

“…The random distribution of Bi and Na on the A site leads to the averaged crystal structure in space group Cc [19] while the structure of BNT for the DFT calculations should have a lower symmetry due to an arrangement of Bi and Na [55]. We selected the monoclinic supercell in space group Pc (BiNaTi 2 O 6 , Z = 4, see Figure 1b), in which the structural feature in the Cc cell can be taken into account.…”

Atomistic origin of huge response functions at the morphotropic phase boundary of(1−x)Na0.5Bi0.5TiO3−xBa

“…The considerable deviation of the short-and intermediaterange order in pure NBT from the long-range order of the average structure was demonstrated by recent x-ray absorption spectroscopy (XAS) [12] and neutron total elastic scattering (TES) [13,14]. Both methods revealed that (i) the off-centering of B-site Ti 4+ cations is only slightly influenced by temperatures and persists in the high-temperature paraelectric phase at least up to 870 K, and (ii) the off-centering of A-site Bi 3+ is considerably larger and less dispersed than that of A-site Na + cations.…”