Low thermal conductivity in nanoscale layered materials synthesized by the method of modulated elemental reactants

We report the room-temperature, cross-plane thermal conductivities, and longitudinal speeds of sound of multilayer films [(TiTe(2))(3)(Bi(2)Te(3))(x)(TiTe(2))(3)(Sb(2)Te(3))(y)](i) (x=1-5, y=1-5) and misfit-layer dichalcogenide films [(PbSe)(m)(TSe(2))(n)](i) (T=W or Mo, m=1-5, and n=1-5) synthesized by the modulated elemental reactants method. The thermal conductivities of these nanoscale layered materials fall below the predicted minimum thermal conductivity of the component compounds: two times lower than the minimum thermal conductivity of Bi(2)Te(3) for multilayer [(TiTe(2))(3)(Bi(2)Te(3))(x)(TiTe(2))(3)(Sb(2)Te(3))(y)](i) films and five to six times lower than the minimum thermal conductivity of PbSe for misfit-layer dichalcogenides [(PbSe)(m)(TSe2)(n)](i). We attribute the low thermal conductivities to the anisotropic bonding of the layered crystals and orientational disorder in the stacking of layered crystals along the direction perpendicular to the surface. (C) 2008 American Institute of Physics.