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Crystal structural and optical properties of Cr-doped Y sub(2)Ti sub(2)O sub(7) and Y sub(2)Sn sub(2)O sub(7) pyrochlores

Pyrochlore-type [A sub(2) super(V) super(I) super(I) super(I)B sub(2) super(V) super(I)O sub(6)O] rare earth stannates (PS) and titanates (PT), doped with increasing amounts of Cr, develop colours ranging from magenta to brown. Combined X-ray and neutron diffraction data revealed that Cr solubility...

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Bibliographic Details
Published in:Acta materialia 2007-04, Vol.55 (7), p.2229-2238
Main Authors: Matteucci, F, Cruciani, G, Dondi, M, Baldi, G, Barzanti, A
Format: Article
Language:English
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Summary:Pyrochlore-type [A sub(2) super(V) super(I) super(I) super(I)B sub(2) super(V) super(I)O sub(6)O] rare earth stannates (PS) and titanates (PT), doped with increasing amounts of Cr, develop colours ranging from magenta to brown. Combined X-ray and neutron diffraction data revealed that Cr solubility in both pyrochlores is very limited, i.e. 0.07 atoms/formula unit in PS and 0.06 atoms/formula unit in PT. A further increase in the Cr amount determines the formation of the YCrO sub(3) perovskite. Diffuse reflectance spectroscopy data showed that the optical properties of Cr-doped yttrium titanates and stannates are rather similar, and that the final colour of the powders is due to the overlapping peaks of Cr super(4) super(+) in the octahedral site of the pyrochlore and of Cr super(3) super(+) in the ternary perovskite. The oxygen occupancy refinement showed that no anion vacancies are formed upon Cr substitution for Sn super(4) super(+) or Ti super(4) super(+), implying that such a charge compensation mechanism does not occur, confirming that the Cr in titanate and stannate pyrochlores is mainly in a tetravalent state.
ISSN:1359-6454
DOI:10.1016/j.actamat.2006.11.008