Nanoscale stacking faults induced low thermal conductivity in thermoelectric layered metal sulfides

Layered metal sulfides (MS)1+x(TiS2)2 (M = Pb, Sn, Bi) with alternative stacking of MS layers and TiS2 layers (a natural superlattice) have been proposed as thermoelectric materials. In this paper, various nanoscale stacking faults have been found in these materials, including the translational disorder in (SnS)1.2(TiS2)2 and the staging disorder in (BiS)1.2(TiS2)2. The lattice thermal conductivities along the layers are systematically and significantly reduced by these stacking faults which are only a few unit cells apart, without deteriorating the electron mobility, demonstrating a “phonon-blocking, electron-transmitting” scenario.