Modification of bismuth telluride for improving thermoelectric properties

A chemical method is used to intercalate lithium ions into the layered structure of bismuth telluride and its relatives. Exfoliation of the intercalated compounds in water results in colloidal suspensions of individual layers. These colloids can then be redeposited onto substrates yielding materials with some c-axis orientation, but no registry of ab planes. Annealing of the deposited materials at a low temperature (85/spl deg/C) for several days or at a higher temperature (300/spl deg/C) for several hours produces highly c-axis oriented materials. N-type doped bismuth tellurides are made by substituting selenium for tellurium in the bismuth telluride lattice. A complete range of solid solutions for Bi/sub 2/Te/sub 3-x/Se/sub x/ (x/spl les/3) has been synthesized from the elements and both the n and c lattice parameters vary linearly with the composition (x). P-type doped bismuth tellurides are made by substituting antimony for bismuth in the bismuth telluride lattice. A complete range of solid solutions for Bi/sub 2-x/Sb/sub 2/Te/sub 3/ (x/spl les/2) has been synthesized from the elements. While the a lattice parameter varies linearly with composition (x), the c parameter remains virtually unchanged as the c-axis size is mainly dependent on the close-packing of tellurium anions and not on the size of the interstitial bismuth or antimony ions.