Lanthanum pyrochlores and the effect of yttrium addition in the systems La2-xYxZr2O7 and La2-xYxHf2O7

Whittle, K. R. and Cranswick, L. M. D. and Redfern, S. A. T. and Swainson, I. P. and Lumpkin, G. R. (2009) Lanthanum pyrochlores and the effect of yttrium addition in the systems La2-xYxZr2O7 and La2-xYxHf2O7. Journal of Solid State Chemistry, 182 (3). pp. 442-450. ISSN 0022-4596 DOI

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The crystal structures of the compounds La2-xYxZr2O7 and La2-xYxHf2O7 with x=0.0, 0.4, 0.8, 1.2, 1.6, and 2.0 have been studied using neutron powder diffraction and electron microscopy to determine the stability fields of the pyrochlore and fluorite solid solutions. The limits of pyrochlore stability in these solid solutions are found to be close to La0.8Y1.2Zr2O7 and La0.4Y1.6Hf2O7, respectively. In both systems the unit cell parameter is found to vary linearly with Y content across those compositions where the pyrochlore phase is stable, as does the x-coordinate of the oxygen atoms on the 48f (x,,) sites. In both systems, linear extrapolations of the pyrochlore data suggest that the disordering is accompanied by a small decrease in the lattice parameter of approximately 0.4%. After the pyrochlore solid solution limit is reached, a sharp change is observed from x~0.41 to 0.375 as the disordered defect fluorite structure is favoured. Electron diffraction patterns illustrate that some short-range order remains in the disordered defect fluorite phases.

Item Type: Article
Uncontrolled Keywords: 08AREP; IA57;
Subjects: 03 - Mineral Sciences
Divisions: 03 - Mineral Sciences
Journal or Publication Title: Journal of Solid State Chemistry
Volume: 182
Page Range: pp. 442-450
Identification Number:
Depositing User: Sarah Humbert
Date Deposited: 30 May 2009 10:33
Last Modified: 23 Jul 2013 09:55

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