Reducing thermal conductivity in thermoelectrica

Thermoelectric materials are able to directly convert thermal energy into electrical energy and reversibly electrical energy into thermal energy. Thermoelectric devices are ideally suited to applications were simplicity and reliability, as well as the absence of moving parts and silent operation outweigh their relatively high cost and low efficiency: spot cooling of electronics, air conditioning, water cooler, cooling of superconducting electronics and infrared detectors or home refrigerators. Moreover, applications are essential, wherever electric energy can be obtained from waste heat gradients. The potential of a material for thermoelectric application is determined by the dimensionless figure of merit, given by the square of the Seebeck coefficient divided by the product of electrical resistivity and thermal conductivity. As the thermal conductivity enters the figure of merit in the denominator, the primary goal of the present proposal is an extensive study of the temperature dependent thermal conductivity of selected samples, as a key parameter controlling the thermoelectric performance. To increase the value of the thermoelectric figure of merit, the absolute values of the thermal conductivity have to be diminished in order to prevent a significant portion of the heat flowing down the temperature gradient. This can be achieved by boosting the number and the intensity of scattering processes. Beside mechanisms which in the past have been employed independently, such as i) atom disorder via simple substitution and ii) phonon scattering on lattice sites by inserting atoms in large cages of the structure (rattling modes); we propose a concept for the efficient reduction of thermal conductivity by combining the above indicated mechanisms simultaneously with scattering of heat carrying phonons on valence fluctuating electrons of atoms with valence instabilities (breathing modes). In this context, the proposed research will focus on families of compounds characterised by strong electron correlations providing extraordinary high density of states at the Fermi level (large thermopower). Promising systems selected under these constraints are i) intermetallics with perovskite type AuCu3, ii) with BaAl4 type and iii) with filled skutterudite type (LaFe4P12). New equipment available for the accomplishment of the proposed project allows a study of the most relevant transport coefficients in an extraordinarily wide temperature range.

Thermoelectric materials are able to directly convert thermal energy into electrical energy and reversibly electrical energy into thermal energy. Thermoelectric devices are ideally suited to applications were simplicity and reliability, as well as the absence of moving parts and silent operation outweigh their relatively high cost and low efficiency: spot cooling of electronics, air conditioning, water cooler, cooling of superconducting electronics and infrared detectors or home refrigerators. Moreover, applications are essential, wherever electric energy can be obtained from waste heat gradients. The potential of a material for thermoelectric application is determined by the dimensionless figure of merit, given by the square of the Seebeck coefficient divided by the product of electrical resistivity and thermal conductivity. As the thermal conductivity enters the figure of merit in the denominator, the primary goal of the present proposal is an extensive study of the temperature dependent thermal conductivity of selected samples, as a key parameter controlling the thermoelectric performance. To increase the value of the thermoelectric figure of merit, the absolute values of the thermal conductivity have to be diminished in order to prevent a significant portion of the heat flowing down the temperature gradient. This can be achieved by boosting the number and the intensity of scattering processes. Beside mechanisms which in the past have been employed independently, such as i) atom disorder via simple substitution and ii) phonon scattering on lattice sites by inserting atoms in large cages of the structure (rattling modes); we propose a concept for the efficient reduction of thermal conductivity by combining the above indicated mechanisms simultaneously with scattering of heat carrying phonons on valence fluctuating electrons of atoms with valence instabilities (breathing modes). In this context, the proposed research will focus on families of compounds characterised by strong electron correlations providing extraordinary high density of states at the Fermi level (large thermopower). Promising systems selected under these constraints are i) intermetallics with perovskite type AuCu3, ii) with BaAl4 type and iii) with filled skutterudite type (LaFe4P12). New equipment available for the accomplishment of the proposed project allows a study of the most relevant transport coefficients in an extraordinarily wide temperature range.