Extremely Low Thermal Conductivity and Enhanced Thermoelectric Performance of Porous Gallium-Doped In2O3

In this paper, Ga-doped In2O3 (IGO) was synthesized using a hydrothermal method combined with spark plasma sintering (SPS) treatment. Nanosized pore structures were successfully introduced into IGO. A high porosity of 67.2% is obtained in the In1.82Ga0.18O3 sample consolidated by SPS sintering at a relatively low temperature of 500 degrees C. With further increasing sintering temperature, the porosity decreases gradually and reaches 10.1% at 1000 degrees C. Positron annihilation measurements confirm the decrease of porosity in IGO with increasing sintering temperature and reveal that there are still considerable amounts of nanopores even after sintering at 1000 degrees C. The nanopores in IGO act as strong phonon scattering centers, which lead to an extremely low thermal conductivity of 0.21 W m(-1) K-1 at room temperature for IGO sintered at 500 degrees C. This thermal conductivity is nearly 2 orders of magnitude lower than that of the fully densified bulk In2O3 and is also the lowest value reported so far. Although the electrical conductivity of IGO is deteriorated by the pore structure, it is overcompensated by the extremely low thermal conductivity. As a result, a high ZT of 0.383 is obtained at 800 degrees C in this sample. Our results indicate that the pore structure can be a competitive strategy to achieve a high ZT value for thermoelectric materials.