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Structural phase transitions and sodium ordering in Na0.5CoO2: a combined electron diffraction and Raman spectroscopy study
- Source :
-
Solid State Communications . May2005, Vol. 134 Issue 6, p403-408. 6p. - Publication Year :
- 2005
-
Abstract
- Abstract: The nonstoichiometric Na x CoO2 system exhibits extraordinary physical properties that correlate with temperature and Na concentration in its layered lattice without evident long-range structure modification when conventional crystallographic techniques are applied. For instance, Na0.7CoO2, a thermodynamically stable phase, shows large thermoelectric power; water-intercalated Na0.33CoO2·1.3H2O is a newly discovered superconductor with T c∼4K, and Na0.5CoO2 exhibits an unexpected charge ordering transition at around T co∼55K. Recent studies suggest that the transport and magnetic properties in the Na x CoO2 system strongly depend on the charge carrier density and local structural properties. Here we report a combined variable temperature transmission electron microscopy and Raman scattering investigation on structural transformations in Na0.5CoO2 single crystals. A series of structural phase transitions in the temperature range from 80 to 1000K are directly identified and the observed superstructures and modulated phases can be interpreted by Na-ordering. The Raman scattering measurements reveal phase separation and a systematic evolution of active modes along with phase transitions. Our work demonstrates that the high mobility and ordering of sodium cations among the CoO2 layers are a key factor for the presence of complex structural properties in Na x CoO2 materials, and also demonstrate that the combination of electron diffraction and Raman spectroscopy measurements is an efficient way for studying the cation ordering and phase transitions in related systems. [Copyright &y& Elsevier]
- Subjects :
- *RAMAN spectroscopy
*ELECTRON diffraction
*ELECTRON microscopy
*SPECTRUM analysis
Subjects
Details
- Language :
- English
- ISSN :
- 00381098
- Volume :
- 134
- Issue :
- 6
- Database :
- Academic Search Index
- Journal :
- Solid State Communications
- Publication Type :
- Academic Journal
- Accession number :
- 17621535
- Full Text :
- https://doi.org/10.1016/j.ssc.2005.02.006