Crystal structure, optical properties, and electronic structure of calcium strontium tungsten oxynitrides CaxSr1-xWO2N

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dc.contributor.authorYashima, Men_AU
dc.contributor.authorFumi, Uen_AU
dc.contributor.authorNakano, Hen_AU
dc.contributor.authorOmoto, Ken_AU
dc.contributor.authorHester, JRen_AU
dc.date.accessioned2014-07-03T04:40:24Zen_AU
dc.date.available2014-07-03T04:40:24Zen_AU
dc.date.issued2013-09-12en_AU
dc.date.statistics2014-07-03en_AU
dc.description.abstractNovel calcium strontium tungsten oxynitrides CaxSr(1-x)WO(2)N (x = 0.25 and 0.5) have been synthesized. The crystal and electronic structures, electron-density distribution, and optical properties of CaxSr(1-x)WO(2)N and CaxSr(1-x)WO(2)N (x = 0, 0.25, and 0.5) have been investigated by neutron, synchrotron, and X-ray powder diffraction; transmission electron microscopy energy-dispersive spectroscopy (TEMEDS); scanning electron microscopy; UV visible reflectance measurements; and ab initio density functional theory (DFT)based calculations. Precursor materials CaxSr(1-x)WO(2)N (x = 0, 0.25, 0.5, and 1) with a scheelite-type structure were prepared by solid-state reactions, and heated at 900 degrees C for 5 h under an ammonia flow. The main phase in the product for the composition x = 1 was metallic tungsten W, whereas cubic Pm3m perovskite-type oxynitrides CaxSr(1-x)WO(2)N were obtained for the compositions x = 0, 0.25, and 0.5. The unit-cell parameter a of the cubic perovskite-type CaxSr(1-x)WO(2)N obtained from the Rietveld analysis of synchrotron X-ray and neutron powder diffraction data decreases with an increase of Ca concentration x (0 < x < 0.5), which indicates the substitution of Ca for Sr. The existence of nitrogen in CaxSr(1-x)WO(2)N was confirmed by (I) the refined occupancy factor in the Rietveld analysis of neutron data and (2) EDS. The maximum-entropy-method electron-density analysis combined with the DFT calculations indicates W N and W-O covalent bonds in CaxSr1_xWO2N, which are formed by the overlapping of W 5d and anion 2p orbitals. The minimum electron density at the W N bond is higher than that at the W-0 one, which indicates that the W N bond is more covalent due to the smaller difference in the electronegativity between W and N atoms compared to the W and O ones: The oxidation number of W in CaxSr(1-x)WO(2)N was estimated to be 5.2 by bond valence sum, which indicates the W5+ ion with the 5di electron configuration. Precursor oxides Ca Sr,,WO, with W6* having the 5cl electron configuration are white and insulating, whereas the CaxSr(1-x)WO(2)N oxynitrides with the W5* ion having the 5di configuration are black and exhibit metallic character. These results indicate the insulator metal transition from the d oxide CaxSr(1-x)WO(2)N to the di oxynitride CaxSr(1-x)WO(2)N. © 2013, American Chemical Society.en_AU
dc.identifier.citationYashima, M., Fumi, U., Nakano, H., Omoto, K., & Hester, J. R. (2013). Crystal structure, optical properties, and electronic structure of calcium strontium tungsten oxynitrides CaxSr1-xWO2N. Journal of Physical Chemistry C, 117(36), 18529-18539. doi:10.1021/jp405597xen_AU
dc.identifier.govdoc5439en_AU
dc.identifier.issn1932-7447en_AU
dc.identifier.issue36en_AU
dc.identifier.journaltitleJournal of Physical Chemistry Cen_AU
dc.identifier.pagination18529-18539en_AU
dc.identifier.urihttp://dx.doi.org/10.1021/jp405597xen_AU
dc.identifier.urihttp://apo.ansto.gov.au/dspace/handle/10238/5731en_AU
dc.identifier.volume117en_AU
dc.language.isoenen_AU
dc.publisherAmerican Chemical Societyen_AU
dc.subjectMagnetic propertiesen_AU
dc.subjectMagnetismen_AU
dc.subjectDiffractionen_AU
dc.subjectNeutron diffractionen_AU
dc.subjectNeutronsen_AU
dc.subjectValenceen_AU
dc.titleCrystal structure, optical properties, and electronic structure of calcium strontium tungsten oxynitrides CaxSr1-xWO2Nen_AU
dc.typeJournal Articleen_AU
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