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Neutron powder diffraction study of defect spinel structures: Tetrahedrally coordinated Ti 4+ in Ni 2.62 Ti 0.69 O 4 and Ni 2.42 Ti 0.74 Si 0.05 O 4
Author(s) -
Lager G. A.,
Armbruster T.,
Ross F. K.,
Rotella F. J.,
Jorgensen J. D.
Publication year - 1981
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s0021889881009321
Subject(s) - octahedron , rietveld refinement , crystallography , spinel , neutron diffraction , diffractometer , chemistry , stoichiometry , powder diffraction , crystal structure , materials science , metallurgy
Cation‐excess spinels with the general formula Ni 2(1 + x ) 2 + (Si 4+ , Ti 4+ ) (1 − x ) O 4 (0.16 ≤ x ≤ 1) can be considered as defect NiO rocksalt structures in which two octahedral metal atoms are replaced by one tetrahedrally coordinated atom. Neutron time‐of‐flight powder data have been collected for two members of the solid‐solution series with the ZING‐P′ high‐resolution diffractometer at Argonne National Laboratory. Least‐squares refinement, using a modified Rietveld profile analysis, confirms that all Ti 4+ in Ni 2.62 Ti 0.69 O 4 [ R (profile) = 3.27%; R (Rietveld) = 9.06%] and Ni 2.42 Ti 0.74 Si 0.05 O 4 [ R (profile) = 3.07%; R (Rietveld) = 8.54%] partially occupies the tetrahedral site 8( a ) ( Fd 3 m ). Ni 2+ totally occupies the octahedral position 16( d ) and partially occupies position 16( c ) which is vacant in stoichiometric spinels. The presence of small amounts of Si 4+ (~ 3 mol%) in the tetrahedral site 8( a ) stabilizes the structure and results in a large decrease [0.0194 (1) Å] in the a cell parameter.