Study of the Stability of Na0.7CoO2 Thermoelectric Materials under Shock Dynamic Loading in a Shock Tube
The thermoelectric material is a material that shows large thermo power, low resistivity and low thermal conductivity. Recently, layered cobalt oxides have been extensively investigated as a promising candidate as thermoelectric material. Important feature of sodium cobalt oxides is that, the sodium ions (Na + ) randomly occupy the regular site by 50% and the sodium content can go up to 70% changes. In this sense layered cobalt oxides, NaCo 2 O 4 should be written as Na x CoO 2 (x = 0.5) and the compound is quite promising for thermoelectric power generation. Terasaki et al. found that a single crystal NaCo 2 O 4 exhibits good thermoelectric property. These layered oxides consist of two layers: CoO 2 layer and Na ion layer. CoO 2 layers acting as an electron reservoir which are responsible for the electrical conductivity and large thermoelectric power. Na ions layer sandwiched between two neighboring CoO 2 layers adjust the concentration of electron in CoO 2 layers and decrease the thermal conductivity along the stacking direction c. Since the discovery of moderately large thermoelectric power (Seebeck coefficient) together with high electrical conductivity in Na x CoO 2(x is 0.70), experiments were done to find new phases for thermoelectric conversion applications. A single-crystal X-ray diffraction study confirmed that Na x CoO 2 (x = 0.74) adopted the hexagonal P63/mmc space group. Neutron diffraction and electron diffraction study shows that the crystal structure of the oxides is strongly dependent on sodium content. The crystal structure of Na 0.75 CoO 2 was studied at ambient and low temperatures down to 10 K at pressures up to 40 GPa using a diamond cell shows an increase in Co-O bond length and decrease in Na-O bond length. Here we present the experimental results on the interaction of shock heated test gases with Na x CoO 2 at high temperature and moderate reflected shock pressure.
KeywordsShock Tube Thermoelectric Property Cobalt Oxide Thermoelectric Material Drive Section
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