Article,
Temperature-induced phase transitions in metastable beta-Ag2WO4: a Raman scattering study
VIBRATIONAL SPECTROSCOPY, (2020)
DOI: 10.1016/j.vibspec.2020.103135
Abstract
Temperature-dependent Raman study was performed in order to obtain
information on structural changes induced by the temperature in the
beta-Ag2WO4 crystal. The stability of the hexagonal structure (P6(3)/m)
phase of the Ag2WO4 crystal was accessed, and our results indicated that
this material undergoes a sequence of three phase transformations, which
were observed at 413-433, 483-493 and at approximately 613 K. In these
tran-sitions, the changes that occurred in the Raman spectra were
characterized by the appearance and disappearance of new Raman bands.
The results lead us to assume the following sequence of phase
transitions: beta to phase II, phase II to phase III, and phase III to
alpha phase. After temperature decreases from the alpha phase at the
highest temperature to room temperature, another phase transition
occurred, but the final phase is not the beta-Ag2WO4 phase. Such phase
transition is irreversible and relates to tilting and/or rotations of
the WO4 tetrahedra, which leads to a disorder at the WO4 sites. The
Principal Component Analysis (PCA) and Hierarchical Cluster Analysis
(HCA) were also performed to evaluate the Raman spectra data of the
beta-Ag2WO4 to identify the correlations with the phase transformations
that occurred during the increasing and decreasing of temperatures.
