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Metallurgical-grade silicon powder (10 m2/g surface area) has been porosified using a metal-assisted chemical etch process based on hydrofluoric acid-ferric chloride chemistry. By controlling the reagent concentrations and ratios, the degree of porosification has been varied. Initiating the reaction at temperatures below 0°C, typically between −15°C and −25°C, yields etched powders with spectacularly increased surface area and pore volume (porosity). The reduced temperature, and its subsequent control, favors pore nucleation and propagation while minimizing bulk chemical etching. Using this process, mesoporous powders with surface areas up to 480 m2/g and pore volumes up to 0.52 ml/g have proved easily achievable at the 10 g batch level.

In the frame of the current research, thep-type Bi2Te3doped (GeTe)0.95(Bi2Te3)0.05alloy composed of hot pressed consolidated submicron structured powder was investigated. The influence of the process parameters (i.e., powder particles size and hot pressing conditions) on both reduction of the lattice thermal conductivity and electronic optimization is described in detail. Very high maximalZTvalues of up to∼1.6 were obtained and correlated to the microstructural characteristics. Based on the various involved mechanisms, a potential route for further enhancement of theZTvalues of the investigated composition is proposed.

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