Publications (2)3.84 Total impact
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Article: Correlation of oxygen vacancy concentration and thermoelectric properties in Na0.73CoO2-δ
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ABSTRACT: In this work, oxygen vacancies were precisely controlled by manipulating oxygen partial pressure and the oxygen partial pressure dependence of thermoelectric properties of polycrystalline Na <sub>0.73</sub> CoO <sub>2-δ</sub> was investigated. The results suggest that resistivity and thermopower augment simultaneously with increasing concentration of oxygen vacancies δ due to the recombination of electrons and holes and average Co valence state. The total thermal conductivity can be reduced by minimizing δ . The dimensionless figure of merit was strongly affected by δ at lower operating temperature. The experimental results provide guideline for the variation in performance of this material system under different processing and operating environments.Applied Physics Letters 05/2010; · 3.84 Impact Factor -
Article: Oxygen Level Dependent Lattice Dynamics of Na0.73CoO2-delta
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ABSTRACT: The optical and acoustic phonon branches of Na0.73CoO2-delta have been determined using Raman scattering and inelastic neutron scatterings, and their correlation with phononic thermal conductivity k(ph) in terms of oxygen-vacancy concentration delta was investigated. The experimentally observed phonon stiffening of the Raman-active E-1g mode suggests that oxygen vacancies may help stabilize texturing of Na ions that gives rise to higher k(ph) with increasing delta. The generalized phonon density of states characterized using inelastic neutron scattering exhibits subtle stiffening of acoustic and optical phonons with delta, which appears to be responsible for the variations in k(ph)(T) profile in the temperature range 323-923 K.Journal of Physical Chemistry C. 01/2010; 114(49):21848-21850.
