Abstract
Raman scattering and infrared transmittance techniques were used to
investigate the room-temperature phonon spectra of the polycrystalline
Ba3In2UO9, Sr3In2UO9, Ba3In2WO9 and Sr3In2WO9 double perovskites.
Although X-ray diffraction has shown that both Ba3In2UO9 and Ba3In2WO9
crystallize in a disordered cubic (Pm (3) over barm-O-h(1)) structure with one formula unit per unit cell (Z = 1), Raman measurements revealed
that both Ba3In2UO9 and Ba3In2WO9 compounds should exhibit a 1:1 ordered
domains with Fm (3) over barm symmetry, embedded in the Pm (3) over barm
matrix. Observation of a nu(1)-like vibration of the InO6 octahedron
reflects the occurrence of a two-phonon-like behavior due to the
intrinsic occupational disorder at octahedral symmetry sites. Assignment
of most of the Raman and infrared phonons is also given. Copyright (C)
2009 John Wiley & Sons, Ltd.
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