Tsygoda V. High-temperature thermoelectric elements based on multicomponent oxygen-free compounds

The thesis' main goal is determination of the influence of technological factors on the microstructure and properties of new conducting materials based on layered anisotropic composites of the «insulator-conductor» type as a part of Si3N4-carbides of transition metals, as well as the employment of these materials in thermoelectric functional elements operating at high temperatures (up to 1100 °C). It has been found that the most promising of such composites are the compositions of Si3N4-ZrC, Si3N4-HfC, in which such phases as SiC, Hf2CN and Zr2CN are formed. It has been shown that the interaction between dielectric matrixes and an additive during the process of high-temperature compression significantly influences the thermoelectric properties of the composite. The violation of stoichiometry causes the growth of the thermoelectromotive force along with the decrease of the electrical conductivity and increase of the defectiveness of n-type materials, as well as growth of the thermoelectromotive force along with an increase both in electrical conductivity and defectiveness of p-type materials. For the first time, the thermoelectric properties of n-type Si3N4-ZrC, Si3N4-HfC; Si3N4-ZrC, Si3N4-WC, Si3N4-TiB2, Si3N4-TaC, Si3N4-TaN composites and p-type Si3N4-C, Si3N4-B4C composites have been researched. It has been shown that cluster percolation structures can be used as thermoelectrodes; the dependence between the thermoelectromotive force and the concentration of the thermoelectric additive is not described by the same mathematical apparatus, as the dependence between the electrical conductivity and the concentration.