Abstract
This paper reports the temperature-dependent study of beta-Ag2MoO4
micro-crystals using Raman spectroscopy. The micro-crystals were
prepared by the hydrothermal method, and lattice dynamic calculations
based on the density-functional theory (DFT) were used to assign the
Raman modes observed in the spectrum and to support the understanding of
the mechanism driving the vibrational changes undergone by beta-Ag2MoO4.
The effect of the temperature on the vibrational properties of the
beta-Ag2MoO4 has been investigated in the temperature range from 300 to
850 K. The Raman data indicated that the crystal exhibits two
temperature-induced phase transformations. One of them was assigned to a
first-order phase transition (from cubic to unknown symmetry) occurring
at about 541 K, connected with some disorder in the MoO4 tetrahedron,
therefore, leading to tiltings and/or rotations of the MoO4 units, as
revealed by changes in the Raman spectra. The second phase transition
was observed at about 700 K, thus leading the crystal to change its
symmetry from the unknown phase to the same cubic room temperature
symmetry (reentrant phase transition). (C) 2016 Elsevier B.V. All rights
reserved.
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