Phonon scattering and stability of Na0.5CoO2
Raman scattering experiments have been performed on NaxCoO2 as a function of temperature at the composition x=0.5 where a structural instability and a metal-insulator transition have been observed. Three additional phonon modes are observed compared to samples with larger x. An in situ annealing study (Tmax = 550K) with the initial presence of water vapor at ambient conditions reveals an irreversible structural instability of this composition.
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