There have been several reports [1, 2, 3] of enhanced ZT at various temperature regimes using superlattice, quantum-dots, and nano-crystalline inclusions, respectively. In combination with semiconductor technology tools for device fabrication, these materials offer unprecedented advantages such as high cooling power density and high-speed cooling/heating in thermal management and high specific power in direct thermal-to-electric power conversion systems. In particular, the thin-film superlattice structures in the p-type Bi2Te3 / Sb2Te3 system has indicated a figure of merit (ZT) of 2.4 near 300K at RTI [1]. While these Bi2Te3-based superlattices are useable in power conversion applications, using small temperature differentials between 300K to 450K, PbTe-based materials are likely to offer a more attractive band gap for power conversion up to 700K as outlined in the announcement N07-086. Thus the development of PbTe-based superlattice would enable the availability of nanoscale materials in the temperature range of 300K to 700K. While PbTe-based quantum-dot superlattice grown by MBE has shown potential ZT of 1.6 at 300K [2] and as high as 3 at higher temperature, it would be advantageous for a lower cost growth method to be employed that would also enable thicker films on the order of 100?m. Nextreme Thermal Solutions, Inc. along with RTI International has developed a simple evaporation method for depositing superlattice films consisting of PbTe and PbTe0.75Se0.25 layers [4]. However, consistently growing thick films on the order of 100?m that maintained the ZT enhancing nanostructure would be a daunting task. An alternative method to reach these thicknesses that could adjoin films together to form a larger bulk material needs to be developed. The use of a compaction process to take thin-film materials and obtain nano-structured bulk materials is proposed.
Keywords: Nano-Structured Bulk,Superlattice,Quantum-Dots,Nano-Crystalline Inclusions,Pbte,P-Type Bi2te3/Sb2te3, Compaction.
