LSCO Ceramics as Possible Thermoelectric Material for Low Temperature Applications
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1044-U06-19
LSCO Ceramics as Possible Thermoelectric Material for Low Temperature Applications Julio E. Rodríguez Departamento de Física, Universidad Nacional de Colombia, Apartado Aéreo 85814, Bogotá, Colombia ABSTRACT Temperature dependent Seebeck coefficient S(T), thermal conductivity κ(T) and electrical resistivity ρ(T) measurements on polycrystalline La1.85Sr0.15CuO4-δ (LSCO) compounds grown by solid-state reaction method were carried out in the temperature range between 100 and 290K. The obtained samples were submitted to annealing processes of different duration in order to modify their oxygen stoichiometry. The Seebeck coefficient is positive over the measured temperature range and its magnitude increases with the annealing time up to approximately 150 µV/K. The electrical resistivity exhibits a metallic behavior, in all samples with ρ(T) values less than 1mΩ-cm. As the annealing time increases, the total thermal conductivity increases to values near 3 W/K-m. From S(T), κ(T) and ρ(T) data, the thermoelectric power factor (PF) and the dimensionless figure of merit (ZT) were determined. These parameters reach maximum values around 25 µW/K2-cm and 0.18, respectively. The observed behavior in the transport properties become these compounds potential thermoelectric materials, which could be used in low temperature thermoelectric applications. INTRODUCTION At low temperature the best thermoelectric material are monocrystalline Bi-Sb alloys, which are n-type semiconductor. However, their use in practical thermoelectric devices is limited by both their poor mechanical properties and because no suitable p-type material has been found with compatible properties. The research for efficient thermoelectric materials that work at room temperature and below has often involved nonconventional semiconductors [1-3]. In this sense, oxide perovskites as: LaCoO3, La1-xSrxCoO3, Bi2Ca2Co2Ox, NaCo2O4, Ca3Co4O9, Ca3Co2O6 are promissory candidates to become thermoelectric materials, because of their transport properties and their physical-chemical stability [4-6]. The La2-xSrxCuO4-δ compounds are members of perovskitesfamily, have tetragonal-symmetry and K2NiF4-type structure. This structure consists of a single CuO2 plane separated by LaO planes. The majority of the transport phenomena in these compounds take place throughout the CuO2 planes, which causes a marked asymmetry of the transport properties and a metallic or semiconducting behavior, which depend on the Sr content and critically on the oxygen stoichiometry [7]. It can be shown that the performance of a thermoelectric device depends on its dimensionless figure of merit ZT, which is given by [1,2]: S 2T ZT = (1) ρκ where S is the Seebeck coefficient, ρ the electrical resistivity, κ the total thermal conductivity and T the absolute temperature. In an electrical conductor, both the charge carriers and phonons transport heat. Hence, κ the total thermal conductivity is composed of two contributions: the heat
conducted by electrons (or holes) and by the crystalline lattice, re
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