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 [(TiTe2)3(Bi2Te3)x(TiTe2)3(Sb2Te3)y]i (x=1−5,y=1−5) and misfit-layer dichalcogenide films [(PbSe)m(TSe2)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 Bi2Te3 for multilayer [(TiTe2)3(Bi2Te3)x(TiTe2)3(Sb2Te3)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.