The Structural Transformation from the Pyrochlore Structure, A₂B₂O₇, to the Fluorite Structure, AO₂, Studied by Raman Spectroscopy and Defect Chemistry Modeling

Authors: Glerup M.¹; Nielsen O.F.¹; Poulsen F.W.²

Source: Journal of Solid State Chemistry, Volume 160, Number 1, August 2001 , pp. 25-32(8)

Buy & download fulltext article:

Price: $52.63 plus tax (Refund Policy)

Abstract:

Pyrochlore oxides of the composition Y₂Ti_2-yZr_yO₇, with y= 0, 0.3, 0.6, and 0.9, were studied using Raman spectroscopy. Doping with Zr⁺⁴, a homovalent ion, gradually induces the material to undergo a structural change from the perfect pyrochlore structure to a defect pyrochlore structure and ends at an oxygen deficient fluorite structure with the formula (Y, Ti, Zr)₁O_1.75. Invoking the bigger Zr⁺⁴ ion on the Ti⁺⁴ site causes this structural transformation. We have also investigated highly Ti-doped YSZ ceramic samples, which all have an oxygen deficient cubic fluorite structure. These samples have formula units between (Y, Ti, Zr)₁O_1.675 and (Y, Ti, Zr)₁O_1.90. It is argued that a band observed at 750 cm^-1 in both the Ti-doped pyrochlore samples and in the Ti, Y, Zr fluorite samples is due to oxygen in seven fold coordination around Ti. Local structures are accordingly observed by Raman in these samples. We finally report a Raman spectrum of orthorhombic Y₂TiO₅. A defect chemistry model has been formulated, which qualitatively describes the observed pyrochlore–fluorite structural transition. Copyright 2001 Academic Press.

Language: English

Document Type: Research article

Affiliations: 1: Department of Chemistry, University of Copenhagen, Universitetsparken 5, Copenhagen Ø, DK-2100, Denmark 2: Risø National Laboratory, Frederiksborgvej 399, Roskilde, DK-4000, Denmark

Publication date: 2001-08-01