Thermoelectric properties and microscopic characterization of Hf doped indium oxide thick film thermocouples screen printed on alumina substrates

The ITHfO slurry was prepared by doping HfO2 into ITO, and In2O3-ITHfO thermocouples were fabricated using screen printing on Al2O3 ceramic substrates. These thermocouples exhibit a temperature limit of 1600℃. Post-annealing at 1250°C resulted in more crystalline films with increased particle size. During this process, Sn2+ in the films oxidised to Sn4+, and the valence of Hf increased. The high-temperature volatilisation of Sn led to a decrease in carrier concentration. However, Hf4+ can substitute for In3+, thereby providing a free electron. This substitution mitigates the reduction in carrier concentration and enhances the upper-temperature measurement capability of the thermocouple. These experimental findings offer a novel approach to doping ITO, aimed at improving the electrical performance of ceramic thermocouples.