Temperature Dependence of Cu₃₋xSb₁₋[subscript y]M[subscript y]S₄ (M=Sn,Ge) Resistivity and Thermopower Public Deposited

http://ir.library.oregonstate.edu/concern/undergraduate_thesis_or_projects/cn69m8700

Temperature dependence measurements of resistivity and thermopower.

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  • Temperature Dependence of Cu3₋xSb1₋yMyS4 (M=Sn,Ge) Resistivity and Thermopower
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  • An experimental apparatus is modified to allow measurements of the Seebeck coefficient and resistivity to be taken simultaneously. This apparatus is designed for bulk and thin film samples between temperatures of 10 K and 300 K. The apparatus is constructed such that these simultaneous measurements do not interfere with each other, minimizing experimental time and overhead associated with each measurement. A COMSOL Multiphysics software model of the current experimental apparatus is constructed. The software model uses the finite element method to solve the heat transfer equation, and indicates that the apparatus can maintain thermal conditions for non-interference between the two measurements. A temperature difference across the sample can be generated to measure the Seebeck coefficient, while the resistivity measurement is performed along an isothermal contour. Using this apparatus, measurements on Cu₃SbS₄ are made to determine the potential of Cu₃SbS₄ as a thermoelectric material. Thermoelectric materials are an active area of research today, with applications in cooling and converting waste heat to useable energy. The resistivity and Seebeck coefficient of bulk Cu₃SbS₄ and doped variants are measured for temperatures between 10 K and 300 K. Bulk Cu₃SbS₄ is found to have a room temperature Seebeck coefficient of 800 μV/K, and a resistivity of 4.5 Ω cm. The resistivity has semiconductor-like behavior, with an activation energy that increases with temperature, opposite to the theoretical prediction. The Seebeck coefficient increases with temperature until 130 K, then decreases with temperature. At temperatures above 130 K, the Seebeck coefficient decreases with increasing temperature, but is not proportional to 1/T. Jonker analysis of the Seebeck coefficient and electrical conductivity does not match a theoretical k/e slope. Doping with 1% Sn reduces the magnitude of the Seebeck coefficient by ~75%, with even larger reductions for 5% Sn and 5% Ge doping. Doping with 3% copper vacancies results in a relatively small, ~20% reduction in the magnitude of the Seebeck coefficient. The resistivity of the sample with 3% copper vacancies has semiconductor-like behavior, while the samples doped with 5% Sn and Ge have a metallic-like resistivity. Cu₃SbS₄ doped with 5% Ge displays the highest power factor of the samples measured. PF=1.04x10⁻⁴ W/K²m is measured for the 5% Ge sample at 300 K.
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