Optimization of Thermoelectric Properties of Mechanically Alloyed p-Type SiGe by Mathematical Modelling

Silicon germanium (SiGe) is a conventional high temperature thermoelectric material, which is usually synthesized through a mechanical alloying route using a ball mill, followed by sintering using a vacuum hot press for fabrication of dense bulk samples. The milling time and sintering temperature are two important parameters that have a major influence on the thermoelectric properties of synthesized samples. In the present work, a simulation technique (i.e., response surface analysis) was employed to study the effect of milling time and sintering temperature on the thermoelectric properties of p-type SiGe. The statistical optimisation of thermoelectric properties was performed using the central composite rotatable design. The responses like electrical resistivity, thermal conductivity, Seebeck coefficient, power factor and the figure-of-merit (ZT) of p-type SiGe alloys were evaluated. The experimental data was fitted to a second order polynomial model and the fitted model was evaluated by regression analysis and analysis of variance (ANOVA). A surprising finding of the analysis is that all responses are optimized at similar values of hot press temperature and ball milling times. There was a model predicted optimum value of ZT = 1.148 at sintering temperature of 1504.5 K and ball milling time of 53.6 h.