Unraveling the structural details and thermoelectric transports of 2D-3D hetero-structure composites

With in-depth research on the thermoelectric properties of the single-phase traditional three-dimensional (3D) and emerging two-dimensional (2D) materials, there is a deficit in the study of the 2D-3D hetero-structure phases, whose structural details and transport features still require a clear understanding. In this work, taking 2D-SnSe and 3D-PbSe as research objects, we prepared mixture-phase composites with the coexistence of 2D and 3D phases and studied the relationship between the thermoelectric transports and phase structures. By conducting the powder X-ray diffraction measurements and Rietveld refinements, we obtained the dynamic 2D-3D hetero-structure compositions of weight percentages with heating-cooling cycles. Subsequently, we estimated the lattice thermal conductivity from the experimental measurements and theoretical calculations as functions of 2D-3D compositions. We discovered that the lattice thermal conductivity reduction became more obvious in the samples with small amounts of hetero-structure phases, benefiting from the extra scattering of phonons by the higher density of hetero-structure interfaces. Moreover, we observed the 2D-3D hetero-structures at the microscopic scale by HADDF-STEM, experimentally confirming the presence of low symmetrical-PbSe and high symmetrical-SnSe phases. This study gave a perspective and investigation method to unravel both the structural details and transport properties of 2D-3D hetero-structure composites, which might provide new strategies for optimizing thermoelectric performance by depressing the thermal transports in hetero-structure materials.