Piezoresistive and thermoelectric properties of semiconducting oxide nanocomposites

Modern aircraft propulsion systems require new engine materials and process technologies that allow turbine engines to be operated at much higher temperatures in order to achieve higher efficiencies and lower emissions. High temperature sensors are required to assess the behavior of such new materials in harsh environments so that structural models can be validated and engine components can be monitored during operation. Thin film semiconducting oxides and nanocomposites based on indium tin oxide (ITO) and other semiconductors are being developed as strain sensors, thermoelectric devices and temperature sensors for high temperature aerospace applications. Self-compensated ITO nanocomposite strain sensors were prepared by reactive co-sputtering from ITO and refractory metal targets (platinum, palladium, nickel, tungsten and NiCoCrAlY) to reduce the effects of apparent strain. Temperature and strain effects on the gage factor of the ITO strain sensors were studied and showed that the diffusion of oxygen through the ITO film was enhanced at high strain levels and elevated temperatures, thus compensating the doubly charged oxygen vacancies that are responsible for the decrease in gage factor. Thermoelectric devices based on n-type and p-type ITO-NiCoCrAlY nanocomposites were fabricated for high temperature energy harvesting to power active wireless strain sensors. Combinatorial materials synthesis was used for thermoelectric materials discovery and to optimize the thermoelectric response of the n-type and p-type ITO-NiCoCrAlY nanocomposites. Thin film ceramic thermocouples based on n-type oxide semiconductors, including oxides including indium oxide (In2O3), tin oxide (SnO2), indium tin oxide (ITO), antimony doped tin oxide (ATO), zinc oxide (ZnO) and aluminum doped zinc oxide (AZO), were also developed to replace noble metal thermocouples inside the hot sections of today\u27s turbine engines used for power generation and propulsion. Thus, a number of oxide thermoelectric materials were developed as part of this thesis that lend themselves to high temperature, oxidizing environments