Bismuth telluride (Bi 2 Te 3 ) is the best-known commercially used thermoelectric material in the bulk form for cooling and power generation applications at ambient temperature. However, its dimensionless figure-of-merit-ZT around 1 limits the large-scale industrial applications. Recent studies indicate that nanostructuring can enhance ZT while keeping the material form of bulk by employing an advanced synthetic process accompanied with novel consolidation techniques. Here, we report on bulk nanostructured (NS) undoped Bi 2 Te 3 prepared via a promising chemical synthetic route. Spark plasma sintering has been employed for compaction and sintering of Bi 2 Te 3 nanopowders, resulting in very high densification (>97%) while preserving the nanostructure. The average grain size of the final compacts was obtained as 90 AE 5 nm as calculated from electron micrographs. Evaluation of transport properties showed enhanced Seebeck coefficient (À120 mV K À1 ) and electrical conductivity compared to the literature state-of-the-art (30% enhanced power factor), especially in the low temperature range. An improved ZT for NS bulk undoped Bi 2 Te 3 is achieved with a peak value of $1.1 at 340 K.

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