Thermoelectric materials have been intensively investigated during the last years for energy harvesting applications. The main drawback of this technology is the low efficiency of the current materials. Significant advances in this respect have been recently achieved by nanostructuring, to mainly reduce the thermal conductivity. In this approach a bulk sample is milled into a nanostructured powder that is then compacted to form a nanobulk sample. The main objective of this thesis is to explore and introduce a new technique, ultrasound milling, based on the crushing of bulk samples by means of ultrasound effects taking place in a liquid medium, for the preparation of nanostructured bulk materials. Bismuth telluride alloys are the industrial standard in thermoelectrics and has been chosen as the material to perform this investigation. The most suitable conditions for the preparation of the nanostructured powders by the ultrasound milling technique have been identified. The optimised powders were used to prepare compacted nanobulk samples. The thermoelectric properties of these samples were finally characterised at room temperature and their performance related to their microstructure. Extraordinarily low thermal conductivity was obtained for both n- and p-type samples prepared (0.5 and 0.35 W/Km respectively), which are within the lowest reported values for any thermoelectric alloy. This reduction was accompanied with a significant decrease in electrical conductivity which led to a non-significant improvement in the figure of merit (Z). However, high ZT values (1 and 1.4 for n- and p-type bismuth telluride respectively) were identified in non-treated samples after a very simple grinding process which was employed as pre-treatment. The figure of merit of these two materials prepared by this simple methodology is close to the best reported values for Bi2Te3. Our results identify ultrasound milling and the simple crushing method as promising tools for the fabrication of nanostructured bulk thermoelectric materials.