The effects of Ca doping content on the crystal structure, electronic transport, thermal transport, and mechanical properties of In2O3 were systematically studied by means of X-ray diffraction (XRD), thermoelectric performance test, and first-principles calculation. XRD analysis shows that Ca2+ can be completely solid-dissolved into the In2O3 lattice to form a single-phase solid solution without the formation of impurity phases, and the lattice constant increases linearly with the increase in doping content, confirming that Ca2+ successfully replaces In3+ and triggers lattice expansion. The results of thermoelectric performance tests show that Ca doping can significantly improve the electrical conductivity of the material. The essence is that Ca doping introduces a large number of free electrons through the charge compensation effect, and coordinately regulates the carrier concentration and mobility to optimize the electronic transport performance. In terms of thermal transport performance, Ca doping leads to a decreasing trend of the total thermal conductivity of the material. The core mechanism is that the difference in ionic radius between Ca2+ and In3+ causes lattice distortion, enhanced mass fluctuation scattering, and defect scattering. At the same time, the decrease in Young’s modulus intensifies phonon scattering, resulting in a significant decrease in lattice thermal conductivity (dominating the change in total thermal conductivity), while the electronic thermal conductivity increases slightly but accounts for a very low proportion. Under the synergistic optimization of electrical and thermal transport, the thermoelectric figure of merit (ZT) of the material increases from ~0.05 to ~0.239, with particularly prominent effects in the medium and high-temperature range.
Zhang et al. (Thu,) studied this question.