Microstructural Evolution and Conductivity Enhancement in Ternary Ag–SnO2–In2O3 Composites via Hot Pressing

To overcome the inherent limitations of Ag–SnO 2 electrical contact materials, this study employed a combined strategy of In 2 O 3 doping and hot pressing sintering, establishing a direct interrelationship among material composition, microstructural evolution, electrical conductivity, and microstrain. Four Ag–SnO 2 –In 2 O 3 powder compositions were synthesized, and the effects of conventional sintering versus hot pressing sintering on microstructure and functional properties were systematically investigated. Results show that hot pressing sintering enables near-complete densification (99% relative density) and significantly improves hardness by 42.5% (57.3HV), primarily by suppressing interfacial porosity and refining microstructural uniformity. Optimal In 2 O 3 addition (4 wt%) not only facilitates homogeneous phase distribution but also minimizes bulk resistivity (2.52 × 10 −6  O·cm), leading to the highest electrical conductivity (3.98 × 10 5  S/cm). Rietveld refinement reveals a pronounced reduction in microstrain (0.01% for In 2 O 3 , 1.7% for SnO 2 ) in the best-performing samples, directly linking lattice relaxation and phase stability to enhanced electron mobility. This mechanistic insight provides a foundation for the rational design and optimization of advanced Ag-based electrical contact materials.