Ultralow thermal conductivity in In2O3 mediated by porous structures

Abstract Two mesoporous In 2 O 3 were prepared with different pore size by using KIT-6 template synthesized at temperature of 50 ° C and 100 ∘ C (designated as 50 ° C– In 2 O 3 and 100 ∘ C– In 2 O 3 ), respectively. Small angle X-ray scattering and transmission electron microscope measurements all confirm ordered pore structure in the synthesized In 2 O 3 . N 2 adsorption/desorption analysis indicates that the pore size in these two In 2 O 3 is about 11.06 nm and 8.737 nm, respectively. Positron lifetime measurements suggest existence of both micropores and mesopores in the porous In 2 O 3 samples, and the mesopore size in 100 ∘ C– In 2 O 3 is smaller than that in 50 ∘ C– In 2 O 3 . The porosity of 50 ° C– In 2 O 3 and 100 ∘ C– In 2 O 3 is about 44% and 40%, respectively. Comparing with the bulk In 2 O 3 obtained by SPS sintering of the commercial In 2 O 3 nanopowders at high temperature of 900 ∘ C, the thermal conductivity of porous In 2 O 3 decreases by more than an order of magnitude. For the 100 ∘ C– In 2 O 3 , the thermal conductivity is as low as 0.58 W m − 1 K − 1 at room temperature of 25 ∘ C, which is below the amorphous limit. On the other hand, the electrical conductivity of the porous In 2 O 3 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 ∘ C for 50 ∘ C– In 2 O 3 , which is almost three times that of the bulk In 2 O 3 .