The preparation and thermoelectric properties of sodium cobalt oxide and oxyhydrates

• Main Authors: K.-Y. Jeng, 鄭凱伊
• Other Authors: 劉嘉吉
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/92682373654501829807

碩士 === 國立彰化師範大學 === 物理學系 === 97 === Abstract Because of its high seebeck coefficient and low electrical resistivity properties, γ-NaxCoO2 is considered as a promising thermoelectric material for high temperature applications. In this study, structure, transport properties of Na-Co-O in which Ca and Li were substituted for Na have been investigated. Oxidants KMnO4 and NaMnO4 were used for partial removal of sodium ions to form Na0.7-x(H2O)yCoO2-δ. For Ca-doped samples, we successfully synthesized γ-Na0.7-xCaxCoO2-δ from XRD diffraction analysis. The valence of Co ion linearly decreases with increasing Ca content, x. Thermopower which is calculated using the generalized Heikes formula, is good agreement with the experimental trend. Power factor of the sample with x = 0.02 is about 57% higher that that of un-doped γ-Na0.7CoO2, indicating a significant improvement. The sodium cobalt oxyhydrates could be obtained by immersing Na0.68Ca0.02CoO2 in aqueous KMnO4 and NaMnO4 solution.Depending on the different molar ratio, we can compound intermediate (c13.8 Å) and dehydrate phase (c11.2Å), but the result of magnetic measurement showed that the samples are not superconductivity. For the molar ratio of NaMnO4/Na is 10X, the magnetization shows a transition at TN～30K. In Na0.7-xLixCoO2-δ series, we have changed experiment parameters but few impurity peaks can be observed for the XRD patterns. Besides, the surface morphology of the Ca3Co3.95Fe0.05O9 and ZnO films was also analyzed by an atomic force microscope (AFM) using AC mode.