Аннотация
Temperature-dependent Raman spectroscopy studies of K2WO4 and MgMoO4
polycrystals were performed in order to obtain information about
vibrational and structural changes in these materials as a function of
temperature. The stability of the monoclinic phase for both K2WO4 and
MgMoO4 samples was assessed and our results indicated that this phase is
stable in the 295-723 K and 300-770 K ranges for K2WO4 and MgMoO4,
respectively. It was observed that both samples underwent two phase
transformations above room temperature. The first phase transformations
which occur at about 633 K and 640 K for K2WO4 and MgMoO4, respectively,
is most likely connected with weak tilting and/or rotations of WO4/MoO4
tetrahedral units that lead to a disorder in the oxygen sublattice.
Raman spectroscopy data also indicated that K2WO4 and MgMoO4 exhibited a
first-order phase transition at around 723 K and 770 K, respectively,
changing from monoclinic to hexagonal symmetry. (c) 2012 Elsevier B.V.
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