Thermoelectric properties of Ag doped Na0.8CoO2 synthesized via citrate-nitrate auto combustion reaction

Masuri, Muhammad Radzi (2018) Thermoelectric properties of Ag doped Na0.8CoO2 synthesized via citrate-nitrate auto combustion reaction. Project Report. Universiti Teknikal Malaysia Melaka, Melaka, Malaysia. (Submitted)

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Abstract

This study focuses on the synthesis of Ag dope with thermoelectric ceramic oxide of NaxCoO2 via citrate-nitrate auto combustion reaction method. The reason of this study is to improve the present ceramic-based thermoelectric NaxCoO2 to achieve higher ZT its current conversion efficiency by material doping. The previous researches of synthesizing the thermoelectric were mostly used the solid state reaction where issues can be found as it has less control of stoichiometry, poor quality of material purity and its homogenous. Thus, in order to achieve a better stoichiometry of the compound and better homogenous also the compound purity, the auto combustion reaction method is highlighted. The concentration of Ag is controlled at 0.1, 0.3, 0.5, 0.7 and 0.9M of concentration in the mixed solution of Ag(NO)3, NaNO3 and Co(NO3)2 as the concentration of Na is at 0.8M of concentration. The mixture of solutions of Ag(NO)3 and Na0.8CoO2 is then dried over 250°C under the UV light and turn into gel state. The combustion properties were observed by using TG-DTA to analyse the weight loss during the drying process. Precursor gels of Na0.8CoO2 Ag-doped were being heated until it achieves the auto combustion reaction which turned the precursor gels into ashes. The ashes from the combustion were calcined at 900°C. Then the powder was continued to be pelletized by using compressive machine at pressure of 14.2 MPa. The size of the pellet was fixed at about 10mm x 2mm diameter. The characterization of the Na0.8CoO2 Ag-doped was performed by using the XRD to study the crystallinity structure and the concentration of Ag in the Na0.8CoO2 Ag-doped. The surface morphology of Na0.8CoO2 Ag-doped was analysed by using SEM. At molarity x = 0.1, 0.3 and 0.5M shows the agglomerated surface structure while x=0.7 and 0.9M showed coarse structure regions. Thermogravitatiometric analysis and differential thermal analysis (TG-DTA) indicated that the precursor gels with molarity x=0.7 decomposed in a single-step reaction combusted at 270°C. Sample with molarity x=0.7 appeared in this work to be the electrically superconducting as measured by using standard four-probe technique.

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