Structural variations in pyrochlore-structured Bi2Hf2O7, Bi2Ti2O7 and Bi2Hf2-xTixO7 solid solutions as a function of composition and temperature by neutron and X-ray diffraction and Raman spectroscopy
Henderson, S.J., Shebanova, O., Hector, A.L., McMillan, P.F. and Weller, M.T. (2007) Structural variations in pyrochlore-structured Bi2Hf2O7, Bi2Ti2O7 and Bi2Hf2-xTixO7 solid solutions as a function of composition and temperature by neutron and X-ray diffraction and Raman spectroscopy. Chemistry of Materials, 19, (7), 1712-1722. (doi:10.1021/cm062864a).
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The structural behavior of the pyrochlore Bi2Hf2O7 with varying temperature has been studied by powder neutron diffraction X-ray diffraction, and Raman scattering. The unit cell undergoes phase changes that are determined by diffraction methods to occur between -, -, - and -polymorphs at around 400, 550 and 900 C. The -Bi2Hf2O7 polymorph corresponds to the ideal cubic pyrochlore phase. Three of the four polymorphs have previously been reported to occur for Bi2Sn2O7. The need to accommodate the active Bi3+ lone pair in the presence of large HfO6 octahedra results in an "icelike" ordering of Bi positions in Bi2Hf2O7 at room temperature. A similar sequence of phase transitions is observed at room temperature with increasing Ti4+ for Hf4+ substitution in the compositional series Bi2Hf2-xTixO7. The structure changes as the space available to the Bi3+ ion increases represent a gradual increase in disorder and symmetry.
|Keywords:||phases, phonon,dielectric-properties, spectrum, dynamics, soft, bi2sn2o7, dependence, srtio3, strontium titanate, crystal-chemistry|
Q Science > QD Chemistry
|Divisions:||University Structure - Pre August 2011 > School of Chemistry
|Date Deposited:||31 Jul 2008|
|Last Modified:||23 Jul 2012 10:42|
|RDF:||RDF+N-Triples, RDF+N3, RDF+XML, Browse.|
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