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Pressure‐ and temperature‐dependent Raman studies of KNbW 2 O 9 hexagonal tungsten bronze
Author(s) -
Mączka M.,
Souza Filho A. G.,
Freire P. T. C.,
Mendes Filho J.,
Kojima S.,
Hanuza J.,
Majchrowski A.
Publication year - 2003
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.975
Subject(s) - raman spectroscopy , orthorhombic crystal system , octahedron , tungsten , bronze , phase transition , crystal structure , materials science , crystallography , hexagonal crystal system , hexagonal phase , phase (matter) , chemistry , analytical chemistry (journal) , condensed matter physics , metallurgy , optics , physics , organic chemistry , chromatography
Pressure‐ and temperature‐dependent Raman studies were performed on KNbW 2 O 9 ferroelectric hexagonal tungsten bronze single crystal. The results suggest that some structural changes, possibly phase transitions, connected with tilting of the WO 6 octahedra occur in this material at around 290–350 K and 1.0–1.4 GPa. No changes in the spectra could be observed at the 523 and 543–553 K phase transitions. The data indicate that these phase transitions lead to only weak changes in the vibrational properties of KNbW 2 O 9 , which were not observed owing to the large bandwidth of the Raman bands. The Raman studies suggest, therefore, that the structure of the unknown phase, existing below 553 K, differs slightly form the orthorhombic structure present above 553 K. The pressure‐dependent study revealed that the 52 cm −1 band, assigned to external vibrations of the WO 6 octahedron, consists at ambient temperature and pressure of two overlapping bands. These bands become well separated at high pressure. Copyright © 2003 John Wiley & Sons, Ltd.