Ultralow thermal conductivity in In2O3 mediated by porous structures

Two mesoporous In2O3 were prepared with different pore size by using KIT-6 template synthesized at temperature of 50 degrees C and 100 degrees C (designated as 50 degrees C-In2O3 and 100 degrees C-In2O3), respectively. Small angle X-ray scattering and transmission electron microscope measurements all confirm ordered pore structure in the synthesized In2O3. N-2 adsorption/desorption analysis indicates that the pore size in these two In2O3 is about 11.06 nm and 8.737 nm, respectively. Positron lifetime measurements suggest existence of both micropores and mesopores in the porous In2O3 samples, and the mesopore size in 100 degrees C-In2O3 is smaller than that in 50 degrees C-In2O3. The porosity of 50 degrees C-In2O3 and 100 degrees C-In2O3 is about 44% and 40%, respectively. Comparing with the bulk In2O3 obtained by SPS sintering of the commercial In2O3 nanopowders at high temperature of 900 degrees C, the thermal conductivity of porous In2O3 decreases by more than an order of magnitude. For the 100 degrees C-In2O3, the thermal conductivity is as low as 0.58 Wm(-1)K(-1) at room temperature of 25 degrees C, which is below the amorphous limit. On the other hand, the electrical conductivity of the porous In2O3 is deteriorated by the pore structure, but it is partially compensated by the increase of Seebeck coefficient. The overall ZT factor increases to higher than 0.08 at 300 degrees C for 50 degrees C-In2O3, which is almost three times that of the bulk In2O3.