Crystal structural and optical properties of Cr-doped Y2Ti2O7 and Y2Sn2O7 pyrochlores
Acta Materialia 55 (2007) 2229–2238
F. Matteucci a, G. Cruciani b, M. Dondi a, G. Baldi c, A. Barzanti c
a ISTEC-CNR, Institute of Science and Technology for Ceramics, Via Granarolo 64, 48018 Faenza, Italy
b Department of Earth Sciences, University of Ferrara, Via Saragat 1, 44100 Ferrara, Italy
c CE.RI.COL., Colorobbia Italia SpA, Via Pietramarina 123, 50053 Vinci, Italy
Pyrochlore-type [A2VIIIB2O6O] 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 YCrO3 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 Cr4+ in the octahedral site of the pyrochlore and of Cr3+ in the ternary perovskite.
The oxygen occupancy refinement showed that no anion vacancies are formed upon Cr substitution for Sn4+ or Ti4+, 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.
© 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. |
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