The thermoelectric effect was first discovered by Thomas Seebeck in 1821 [1] when he discovered that twisting two wires together and twisting one end induced a voltage. The converse effect, that is, application CHIR-258 of voltage to induce a temperature gradient across the thermoelectric material, was discovered by Jean Peltier [1] in 1834, and is thus called the Peltier effect. The performance of the thermoelectric material is evaluated by the dimensionless figure of merit (ZT), ZT = ��S2T/K, where �� is the electrical conductivity, K is the thermal conductivity, T is the absolute temperature, and S is the Seebeck coefficient (S = ��V/��T, that is, the ratio of the induced voltage over the temperature gradient across the thermoelectric device) [2].

Thus, a high performance thermoelectric material requires high electrical conductivity, Seebeck coefficient, and low thermal conductivity. It is really challenging to find a material which has a high Seebeck coefficient (S) in combination with high electrical conductivity (��) and low thermal conductivity (k). In most materials, the electrical conductivity is directly proportional to the thermal conductivity. An ideal TE material would possess a high Seebeck coefficient as in the crystalline semiconductor, high electrical conductivity as in the crystalline metal, and low absolute temperature as in glass [4]. For practical applications, such as thermal generators (TEGs), a ZT of more than 3 is required, whilst the best efforts currently only produce a ZT of 3 [5].

Early thermoelectrical devices developed in the early 1960s earned some popularity given the solid state nature of the devices, that is, no moving parts compared to generators and motors. These devices were mainly based on Bi2Te3 [6, 7]. However, these devices have low efficiency (ZT < 1, and a system efficiency of <10%) and are therefore not cost-effective in most applications. In the mid-1990s, a research on thermoelectric started to gain interest again after theoretical predictions suggested that the thermoelectric efficiency could be enhanced through nanostructuring [8]. The introduction of nanostructures in thermoelectric materials served either to increase the electrical conductivity (through quantum dots), or to decrease the thermal conductivity (through nanowires and amorphous structures) [9�C11].

Currently, the TE communication has paid the most attention on skutterudites [12], half-Heusler alloys [13], clathrates [14], and pentafluoriade [15]. The common characteristic of these materials is their complex structure, which serves to reduce the thermal conductivity and hence increase the ZT. These materials are usually Batimastat targeted for high temperature operation, such as electricity generation from waste heat of industrial sources, such as steel furnaces and aluminum melting. This is due to their optimal ZT in a temperature range of 600K or higher.