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An Unexpected Crystal‐Chemical Principle for the Pyrochlore Structure
Author(s) -
Vanderah Terrell A.,
Levin Igor,
Lufaso Michael W.
Publication year - 2005
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.200500234
Subject(s) - pyrochlore , chemistry , crystallography , crystal structure , metal , phase (matter) , ion , inorganic chemistry , organic chemistry
Phase equilibrium studies of the Bi–Zn–Nb–O system show that pyrochlore does not form at chemical compositions predicted by the traditional formula for this crystal structure, A 2 B 2 O 6 O', where A denotes large (8‐coordinated, e.g. Bi 3+ ) and B small (6‐coordinated, e.g. Zn 2+ , Nb 5+ ) cation sites. Instead, pyrochlore forms only at compositions with excess B cations which, surprisingly, occupy the large A‐cation sites. Reports of similar behavior in other pyrochlores suggest a previously unrecognized inherent structural feature (displacive disorder) which allows the formation of a large family of cubic pyrochlores with small B cations occupying up to ca. 25 % of the large A‐cation sites. Many pyrochlores can now be synthesized by deliberately combining large and small metal ions on the A sites. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)