Temperature induced phase transformations on the Li2MoO4 system studied by Raman spectroscopy
Abstract
The present research reports results of lattice dynamics calculations and temperature-dependent Raman scattering study of the dilithium molybdate system, Li2MoO4, in the 25-600 °C temperature range. The effects of the temperature duly produced gradual changes, associated with the disorder and anharmonic effects followed by thermodynamic instability, leading the structure to a phase transformation. Calorimetric measurements up to 1000 °C corroborated that the crystal structure experienced gradual modifications, characterized by changes in the DSC base line. These stated thermal events as well as the changes in the profile of the Raman spectra, suggested that a phase transformation is connected with tilting and/or rotations of the MoO4 tetrahedron leading to a disorder in the MoO4 sites. The observation of one exothermic peak on the DSC curve at about 702 °C is related with the melting in the sample. The experimental results were discussed based on the mode assignments performed by using lattice dynamics calculations from where we predicted both wavenumbers and atomic displacements.
- Publication:
-
Journal of Molecular Structure
- Pub Date:
- July 2017
- DOI:
- 10.1016/j.molstruc.2017.03.038
- Bibcode:
- 2017JMoSt1139..119S
- Keywords:
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- Dilithium molybdate;
- High temperature;
- Raman scattering;
- Phase transformations;
- Trigonal phase