Structure and thermoelectric properties of new layered compounds in the quaternary system Cs-Pb-Bi-Te

By introducing of various equivalents of PbTe into the layered framework of CsBi₄Te₆, the four new compounds CsPbBi₃Te₆ (1), CsPb₂Bi₃Te₇ (2), CsPb₃Bi₃Te₈ (3) and CsPb₄Bi₃Te₉ (4), were discovered. The compounds adopt layered structures built up of anionic slabs of progressively increasing thickness. The [Pb_mBi₃Te_5+m]^- (m = 1, 2, 3, 4) slabs in the four structures can be viewed as fragments excised from the PbTe-type structures with 4-, 5-, 6- and 7-monolayers, respectively. As prepared, these materials are off-stoichiometric and n-type conductors. We present preliminary results of the crystal structures and thermoelectric properties of these materials and classify them as members of the new homologous series CsPb_mBi₃Te_5+m (m = 1 to 4).