Executive Summary : | Heat generated from various sources viz. automobile engines, boilers in industries, Sun’s heat goes wasted and need to be tapped for useful energy conversion. This becomes more important as the fossil fuels which form the source of energy for most of our day-to-day activities are available only for few decades. Based on the Seebeck and Peltier effects, it is possible to convert the available heat energy to electrical energy and vice versa. Semiconductors which do this conversion are called thermoelectric materials and form the basis for the current project proposal. The heat to electricity energy conversion of a thermoelectric material is given by the ratio of its power factor and thermal conductivity. For a high performance thermoelectric material the desirable criteria is a high power factor and a low thermal conductivity which is a daunting task as an increase in electronic conductivity will result in reducing the Seebeck coeffecient and increase electronic contribution to the thermal conductivity. The non-oxides viz. Bi2Te3, SiGe, PbTe, filled skutterudites exhibit the highest ZT due to their optimum to narrow band gaps and phonon scattering centres. The commercialization of these compounds has only been limited to few of them viz. Bi2Te3 owing to their toxicity. Oxides on the other hand have a great chemical stability at high temperatures, non-toxic, low cost and ease of manufacturing are more suitable for most of the commercial heat to electrical energy conversion applications. The research in oxide did not gain importance mostly due to their low electrical and high thermal conductivity until the discovery of NaCoO₂ which showed simultaneously a high Seebeck coeffecient and electrical conductivity. This was attributed to the strong correlation existing in the CoO2 layers between Co³+ and Co4+ cations. The objective of the current proposal is to reduce the thermal conductivity of some high ZT oxide system by carrying out same site multivalent ion doping. Two p-type layered thermoelectric materials viz. Ca3Co4O9 and BiCuOSe will be taken and multivalent doping will be carried out at the specific sites in their crystal structures. In terms of appllication, a high dimensionless figure of merit p-type semiconductor can be achieved at the end of the project which can be coupled with an n-type leg to build a thermoelectric module. A device can be built in collaboration with electrical engineering department and out put power be measured. If reasonable output power is obtained it can be given to an industry for further testing and commercialization. |