Аннотация
The crystalline structure of NaCaMg2F7 was determined using single
crystal X-ray diffraction. This compound crystallizes in the cubic
pyrochlore structure, i.e., space group Fd (3) over barm, lattice parameter: a = 10.2610(5) Angstrom and Z = 8. All atoms occupy special
crystalline sites, but Na and Ca are randomly distributed in the
anti-cristobalite sub-lattice of the pyrochlore structure. The
vibrational spectrum was determined by polarized Raman scattering and
infrared reflectance. The number of observed Raman and infrared active
phonons is larger than that predicted by the factor group analysis of
the pyrochlore structure. The anomalous vibrational spectrum is
discussed in terms of a disorder-induced symmetry lowering mechanism.
(C) 2004 Elsevier Inc. All rights reserved.
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