Phonon scattering and stability of

Raman spectroscopy study ofα-,β-,γ−NaxCoYang1, Xia2, Shi3 et al. 2006Phys. Rev. B30160View full textAdd to dashboardCite

“…Theoretical analysis based on lattice shell model and first-principle calculations have also been performed for typical Na x CoO 2 materials with x = 1.0, 0.74, 0.5, and 0.3, 5,12 however, much controversy still remains in related published results. [4][5][6][7][8][9][10][11][12][13] Qu et al observed three phonon modes in the experimental spectrum of Na 0.7 CoO 2 , 13 in sharp contrast with our previously reported data which clearly demonstrated five Ramanactivated modes for ␥-Na 0.75 CoO 2 . 4 Moreover, remarkable spectral differences also exist in the charge-ordered Na 0.5 CoO 2 material as reported in Refs.…”

“…Moreover, the two modes that appear at 560 and 595 cm − As mentioned in the introduction part, the Ramanscattering measurements on Na x CoO 2 materials ͑polycrystalline samples or single crystals͒ performed in several laboratories show apparently different spectral features. [4][5][6][7][8][9] Here we make a brief discussion on the samples used for experimental investigations. In our previous publication, we identified that five active phonons generally appear in the Raman spectra of ␥-Na x CoO 2 by using ␥-Na 0.7 CoO 2 single crystals grown by the flux method.…”

“…Layered Na x CoO 2 materials have been extensively investigated in recent years due to a notably large thermoelectric power coexisting with superconductivity and complex charge-ordering (CO) transitions [1][2][3]. In order to understand the lattice dynamics in this layered system, Raman scattering [4][5][6][7][8][9], infrared absorption [10], and neutron scattering experiments [11] have been carried out in numerous laboratories and under different experimental conditions. Theoretical analysis based on lattice shell model and first principle calculations have also been performed for typical Na x CoO 2 materials with x = 1.0, 0.74, 0.5 and 0.3 [5,12], however, much controversy still remains in related published results [4][5][6][7][8][9][10][11][12][13].…”

Enhanced low-energy fluctuations and increasing out-of-plane coherence in vacancy-ordered NaxCoO2

“…Co ion charge ordering leads to a multiplication of low-energy modes as observed, e.g. for x=0.5 [16]. In the presently studied Na-vacancy ordered compositions, two in-plane modes are observed in the frequency range Δω ≈ 440-490 cm -1 .…”

Structural changes of NaxCoO2 (x=0.74) at high pressures

“…There are several reports [20][21][22][23] up to now on the Raman measurements for the nonhydrated and hydrated Na x CoO 2 with different Na content. The reported Raman active modes and their positions are not well in agreement from one another.…”