Abstract:
Thermoelectric device is the direct conversion of temperature differences to electric voltage and vice-versa. The thermoelectric device composed of a material which is able to create a voltage when there is a different temperature on each side. In this study, polycrystalline NaxCo₂O₄ ceramic samples were prepared by conventional powder mixing or solid state reaction method using Na₂CO₃ and Co₃O₄ as starting raw materials. Compared with sol-gel method, NaNO₃, Co(NO₃)₂.6H₂O, citric acid and ethylene glycol were used in various on starting chemical. Phase analysis and physical properties of NaCo₂O₄ specimens were characterized and compared. The thermoelectric properties were measured in the temperature range of room temperature to 700℃ The thermal conductivity was calculated from heat capacity, bulk density and thermal diffusivity measured by a laser flash method using (TC7000). Seebeck coefficient and resistivity were measured simultaneously using Seebeck measurement instrument (ZEM-2) in He atmosphere. The NaxCo₂O₄ samples were compacted with varied sintering temperature of 870 890 910 and 930℃. The results showed that the preparation by mixing the powder with calcined temperature at 850℃ for 12 hours ground by hand with agate mortar then sintered at 910℃ show highest ZT as 0.239 at 700℃. Synthesis by sol-gel with calcined temperature at 850℃ for 12 hours sintering at 890℃ showed highest ZT value of 0.132 at 600℃.