Thermoelectric (Peltier) heat pumps are capable of refrigerating solid or fluid objects, and unlike conventional vapor compressor systems, they can be miniaturized without loss of efficiency. More efficient thermoelectric materials need to be identified, especially for low-temperature applications in electronics and devices. The material CsBi(4)Te(6) has been synthesized and its properties have been studied. When doped appropriately, it exhibits a high thermoelectric figure of merit below room temperature (ZT(max) approximately 0.8 at 225 kelvin). At cryogenic temperatures, the thermoelectric properties of CsBi(4)Te(6) appear to match or exceed those of Bi(2-x)Sb(x)Te(3-y)Se(y) alloys.

The highly anisotropic material CsBi(4)Te(6) was prepared by the reaction of Cs/Bi(2)Te(3) around 600 degrees C. The compound crystallizes in the monoclinic space group C2/m with a = 51.9205(8) A, b = 4.4025(1) A, c = 14.5118(3) A, beta = 101.480(1) degrees, V = 3250.75(11) A(3), and Z = 8. The final R values are R(1) = 0.0585 and wR(2) = 0.1127 for all data. The compound has a 2-D structure composed of NaCl-type [Bi(4)Te(6)] anionic layers and Cs(+) ions residing between the layers. The [Bi(4)Te(6)] layers are interconnected by Bi-Bi bonds at a distance of 3.2383(10) A. This material is a narrow gap semiconductor. Optimization studies on the thermoelectric properties with a variety of doping agents show that the electrical properties of CsBi(4)Te(6) can be tuned to yield an optimized thermoelectric material which is promising for low-temperature applications. SbI(3) doping resulted in p-type behavior and a maximum power factor of 51.5 microW/cm.K(2) at 184 K and the corresponding ZT of 0.82 at 225 K. The highest power factor of 59.8 microW/cm.K(2) at 151 K was obtained from 0.06% Sb-doped material. We report here the synthesis, physicochemical properties, doping characteristics, charge-transport properties, and thermal conductivity. Also presented are studies on n-type CsBi(4)Te(6) and comparisons to those of p-type.

A New Thermoelectric Material: CsBi 4 Te 6 . -The title compound is obtained in quantitative yield by reaction of Cs 2 Te and Bi 2 Te 3 at 700°C (60 h). CsBi 4 Te 6 crystallizes in the monoclinic space group C2/m with Z = 8 (single crystal XRD). The structure consists of NaCl-type [Bi4 ] layers and Cs + ions residing between the layers. The anionic layers are interconnected by Bi-Bi bonds with a distance of 3.2383 Å. CsBi 4 Te 6 is a narrow gap semiconductor. The electrical properties can be tuned by doping to yield an optimized thermoelectric material which is promising for low-temperature applications. SbI3 doping results in p-type behavior and a maximum power factor of 51.5 µW/cm·K 2 at 184 K and the corresponding thermoelectric figure of merit ZT of 0.82 at 225 K. The highest power factor of 59.8 µW/cm·K 2 at 151 K is observed for the 0.06% Sb-doped material. -(CHUNG, D.-Y.; HOGAN, T. P.; ROCCI-LANE, M.; BRAZIS, P.; IRELAND, J. R.; KANNEWURF, C. R.; BASTEA, M.; UHER, C.; KANATZIDIS*, M. G.; J. Am. Chem. Soc. 126 (2004) 20, 6414-6428; Dep. Chem., Mich. State Univ., East Lansing, MI 48824, USA; Eng.) -Schramke 33-018 Te -6