title: (23)Na multiple-quantum MAS NMR of the perovskites NaNbO(3) and NaTaO(3).
abstract: The distorted perovskites NaTaO(3) and NaNbO(3) have been studied using (23)Na multiple-quantum (MQ) MAS NMR. NaTaO(3) was prepared by high temperature solid state synthesis and the NMR spectra are consistent with the expected room temperature structure of the material (space group Pbnm), with a single crystallographic sodium site. Two samples of NaNbO(3) were studied. The first, a commercially available sample which was annealed at 900 degrees C, showed two crystallographic sodium sites, as expected for the room temperature structure of the material (space group Pbcm). The second sample, prepared by a low temperature hydrothermal method, showed the presence of four sodium sites, two of which match the expected room temperature structure and the second pair, another polymorph of the material (space group P21ma). This is consistent with powder X-ray diffraction data which showed weak extra peaks which can be accounted for by the presence of this second polymorph. Density functional theory (DFT) calculations support our conclusions, and aid assignment of the NMR spectra. Finally, we discuss the measured NMR parameters in relation to other studies of sodium in high coordination sites in the solid state.
authors.affiliation: Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, UK CB2 3EQ. sema@st-andrews.ac.uk
authors.forename: Sharon E
authors.initials: SE
authors.lastname: Ashbrook
authors.forename: Laurent
authors.initials: L
authors.lastname: Le Pollès
authors.forename: Régis
authors.initials: R
authors.lastname: Gautier
authors.forename: Chris J
authors.initials: CJ
authors.lastname: Pickard
authors.forename: Richard I
authors.initials: RI
authors.lastname: Walton
mesh_terms: D017610:Calcium Compounds / Q000032:analysis / Q000737:chemistry*; D003198:Computer Simulation; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D009556:Niobium / Q000032:analysis / Q000737:chemistry*; D010087:Oxides / Q000032:analysis / Q000737:chemistry*; D011789:Quantum Theory; D012964:Sodium / Q000032:analysis / Q000737:chemistry*; D012975:Sodium Isotopes; D013635:Tantalum / Q000032:analysis / Q000737:chemistry*; D014025:Titanium / Q000032:analysis / Q000737:chemistry*
chemical_list: D017610:Calcium Compounds; D010087:Oxides; D012975:Sodium Isotopes; D009556:Niobium; C059910:perovskite; D013635:Tantalum; D012964:Sodium; D014025:Titanium; C073337:niobium pentoxide; C078151:tantalum oxide