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

Different types of polymers can be intercalated into R-RuCl 3 with different synthetic methodologies. Polyaniline/R-RuCl 3 nanocomposite was prepared by the in situ redox intercalative polymerization method, in which R-RuCl 3 was exposed to an aniline/acetonitrile solution in open air. Water-soluble polymers such as poly(ethylene oxide), poly(vinyl pyrrolidone), and polyethylenimine were intercalated by an encapsulative precipitation method using monolayer suspensions of R-RuCl 3 . A modification of this method led to insertion of polypyrrole. Monolayer suspensions of R-RuCl 3 can be prepared from Li x RuCl 3 (x ∼ 0.2). The latter is produced by the reaction of R-RuCl 3 with 0.2 equiv of LiBH 4 . The polymer insertion is topotactic and does not cause structural changes to the host. The metal chloride layers in these materials possess mixed valency. The reduction and polymer intercalation of R-RuCl 3 alters the intralayer and interlayer Ru 3+ (low spin d 5 ) magnetic coupling, so that interesting magnetic properties appear in the nanocomposites. In addition, the reduction brings in free hopping electrons to the RuCl 3 layers and the polymer intercalation builds up new electronic or ionic conducting channels in the galleries, so that the charge transport properties are changed dramatically. For example, Li x RuCl 3 shows an electrical conductivity 3 orders of magnitude higher than pristine R-RuCl 3 at room temperature and Li x (PEO) y RuCl 3 has an ion conductivity comparable with the best (lithium salt)-polymer electrolytes. For a comprehensive understanding of the structure of the representative nanocomposite Li x (PEO) y RuCl 3 , the arrangement of polymer chains inside the galleries was explored with analysis of its one-dimensional (00l) X-ray diffraction pattern. Calculated electron density maps along the stacking c-axis lead to a structural model that fills each gallery with two layers of polymer chains exhibiting a conformation found in type-II PEO-HgCl 2 . The most consistent PEO arrangement in the gallery generates oxygen-rich channels in the middle of the gallery in which the Li ions can reside. The new nanocomposites were characterized with thermogravimetric analysis, infrared spectroscopy, powder X-ray diffraction, magnetic measurements, as well as electrical and ionic conductivity and thermopower measurements.

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