One-Order Decreased Lattice Thermal Conductivity of SnSe Crystals by the Introduction of Nanometer SnSe2 Secondary Phase

In recent years, the layered semiconductor tin selenide (SnSe) has been of great interest in the thermoelectric field because of its remarkable thermoelectric potential. Here, the as-grown Sn0.98Se crystal was found to induce a random secondary phase of SnSe2 in the host SnSe crystal due to similar formation enthalpy between SnSe and SnSe2. In addition, we carefully studied the thermal transport properties of as-grown Sn0.98Se crystals and intrinsic SnSe crystals. The Umklapp scattering is the prominent scattering and results in a low thermal conductivity of 0.77 W/m/K at room temperature along a direction in the intrinsic stoichiometry SnSe crystal. Because of the optical phonon contribution suppressed by the nanoscopic SnSe2 intercalations in the as-grown Sn0.98Se crystal, the thermal conductivity further decreased to 0.45 W/m/K in nonstoichiometric as-grown Sn 0.98 Se crystals, which is a two-fold reduction and close to that of amorphous compounds. Our study may shed more light on the origin of the extra low thermal conductivity in as-grown Sn0.98Se crystals and may provide an efficient way to modulate thermal conductivity by microstructure engineering.