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Temperature‐induced phase transformations in Na 2 WO 4 and Na 2 MoO 4 crystals
Author(s) -
Lima C. Luz,
Saraiva G. D.,
Freire P. T. C.,
Maczka M.,
Paraguassu W.,
de Sousa F. F.,
Mendes Filho J.
Publication year - 2011
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.2759
Subject(s) - raman spectroscopy , crystallography , phase transition , phase (matter) , crystal (programming language) , crystal structure , order (exchange) , chemistry , tetrahedron , materials science , condensed matter physics , physics , optics , organic chemistry , computer science , programming language , finance , economics
Temperature‐dependent Raman studies on Na 2 WO 4 and Na 2 MoO 4 crystals were performed in order to obtain information on structural changes induced by temperature evolution. The stability of the cubic phase of Na 2 WO 4 and Na 2 MoO 4 crystals was assessed and our results indicate that this phase is stable in the 8–823 K and 15–773 K ranges for Na 2 WO 4 and Na 2 MoO 4 , respectively. The crystal of Na 2 WO 4 shows a phase transition occurring at 833 K. Na 2 MoO 4 undergoes a sequence of three phase transitions, which were observed at 783–803, 823–913 and 943–950 K. In both crystals, a strong first‐order phase transition occurs as indicated by the behavior of the Raman modes: the Raman bands split and new bands appear below 100 cm −1 . These transitions are connected with tilting and/or rotations of the WO 4 and MoO 4 tetrahedra, which leads to a disorder at the WO 4 and MoO 4 sites. Copyright © 2010 John Wiley & Sons, Ltd.