Resistivity and Thermoelectric power of NaxCoO2 (x =1.0, 0.7 and 0.6) system

H. Kishan; V. P. S. Awana; M. A. Ansari; Anurag Gupta; R. B. Saxena; V. Ganesan; A. V. Narlikar; C. A. Cardoso; R. Nirmala; Devendra Buddhikot; S. K. Malik

doi:10.1063/1.1847852

arXiv · cond-mat/0412122

Resistivity and Thermoelectric power of NaxCoO2 (x =1.0, 0.7 and 0.6) system

H. Kishan·V. P. S. Awana·M. A. Ansari·Anurag Gupta·R. B. Saxena·V. Ganesan·A. V. Narlikar·C. A. Cardoso·R. Nirmala·Devendra Buddhikot·S. K. Malik

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Abstract

Results of thermo-electric power (S) and electrical resistivity (r) measurements are reported on NaxCoO2 compounds with x = 1.0, 0.7 and 0.6. These are single-phase compounds crystallizing in the hexagonal structure (space group P63/mmc) at room temperature. Thermo-electric power values at 300K (S300K) are, 80mV/K, 39mV/K and 37mV/K for x = 1.0, 0.7 and 0.6 samples, respectively. The samples with x=0.7 and 1.0 are metallic down to 5 K, while the x = 0.6 sample is semiconducting. The value of r300K for x = 1.0 sample is \~0.895 mW-cm and the power factor (S2/r) is = 7.04 x 10-3 W/mK2 which qualifies it as a good thermo-electric material. In x =1.0 sample, S(T) is positive throughout 300-5K temperature range and decreases monotonically to zero as temperature T= 0. In contrast, S(T) of x = 0.7 and 0.6 samples changes sign and shows negative values between 90 K and 16 K before approaching zero as T = 0. Anomalous S(T) behavior of x = 0.6 and 0.7 samples, which are coincidentally the precursor materials to the reported superconductivity in this class of materials, indicates a dramatic change in the electronic structure of these compounds on lowering the Na content.

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H. Kishan, V. P. S. Awana, M. A. Ansari, Anurag Gupta, R. B. Saxena, V. Ganesan, A. V. Narlikar, C. A. Cardoso, R. Nirmala, Devendra Buddhikot, S. K. Malik. 2004-12-06. Resistivity and Thermoelectric power of NaxCoO2 (x =1.0, 0.7 and 0.6) system. https://doi.org/10.1063/1.1847852

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