ICT2014 Abstracts

ZnSb has been known as a thermoelectric material for a long time. A renewed research interest in the material has emerged by the possibilities of improved efficiency by nanostructuring, as studied for many material systems recently. In the literature, several different effects and approaches have been studied which affect various thermoelectric properties using nanostructuring. Here we have investigated the effect of cryomilling in the synthesis processes of undoped ZnSb.

Nanopowders of ZnSb were prepared by cryomilling where the material was embrittled due to cooling by liquid nitrogen. The resulting powder was studied by X-ray Diffraction, Transmission Electron Microscopy and Dynamic Light Scattering. The mean nanoparticle size was found to be about 10 nm. A series of experiments were designed where the powders were pressed into pellets by two different sintering techniques, here termed: annealing hot press (AHP) and rapid hot press (RHP). Dry ball-milling at room temperature was compared to ball-milling at cryogenic temperature. The cryomilled powder exhibited grain growth after hot-press at 300-470°C, e.g. hot-press at 470°C for 40 min resulted in grain sizes of approximate 200 nm. The thermal conductivity was measured by the laser flash technique, and ZnSb synthesized by cryomilling and RHP sintering displayed a reduction of thermal conductivity by up to 30% compared to samples synthesized by RT ball-milling and AHP. The carrier concentration, resistivity and mobility were measured for the temperature range 300-700 K. The figure of merit for undoped ZnSb cryomilled samples was larger than 0.6 and the carrier concentration was around 3x10¹⁹cm^-3 at 450°C.  Some synthesis parameters bring an instability which is currently investigated.