Oxide Thermoelectric

Thermoelectric oxides have their potential advantages over other existing choices in terms of chemical and thermal robustness, weak toxic nature, high thermal stability and excellent oxidation resistance for efficient energy conversion applications. Our area of interest is Transition metal oxides due to its strong electronic correlations and strong spin and orbital fluctuations, as well as high degeneracy in the narrow d-bands, which are advantageous for improving thermoelectric performance. The degree of goodness for TE material is characterized by dimensionless ZT parameter ZT =S²σT/(κ_e + κ_l) where, each parameter S (Seebeck coefficient), σ (electrical conductivity), κ_e (electronic thermal conductivity), κ_l (lattice thermal conductivity ) and T (absolute temperature) are interdependent; therefore, it is a challenge to increase ZT by optimizing these parameters. From initial observations, it is well documented that carrier concertation about 10¹⁸-10²¹ have maximum power factor (S²σ), hence highly degenerate semiconducting materials are prominent choice for TE applications.

Studies of thermoelectric parameters with CFMS-PPMS system

For studying thermoelectric parameters and correlated magnetic properties of the samples, we have standard cryo-free magnetic system (CFMS) in which various assemblies allow to measure different physical properties like magnetization, resistivity, Hall coefficient, AC-susceptibility along with transport properties like thermal conductivity and specific heat capacity in temperature range of 1.7-400K with magnetic field of ± 14Tesla. The geometry of thermal transport measurement is such, the temperature measurement is taken from directly from the sample between the temperature heat source and sink. The thermal conductivity and Seebeck coefficient measurement are taken in single shot experiment. The specific heat capacity measurement works on the principle of relaxation time for the heat on the sample, where heat is given in short pulses. By calculating time constants and background thermal conductance, the sample specific heat is calculated very precisely. The sample mounting of the sample can be seen by following fig. for both thermal conductivity and specific heat respectively.

For Lanthanum-cobaltite based samples, we measure thermoelectric parameters profiles with different field and temperatures, to analyse their inter-correlations. The approach of decoupling the quantities derived from the Boltzmann transport equation by maximising S and σ for “electron crystal” and minimising the lattice contribution to the thermal conductivity (κ_l) to achieve “phonon glass” is followed. This enable us to understand clear views for cumulative and individual dependencies of respective parameter to improve ZT parameter in oxides system.