An ultra-low thermal conductivity compound with the ideal formula [(PbSe)1.00]1[MoSe2]1 has been successfully crystallized across a range of compositions. The lattice parameters varied from 12.41 Å to 12.75 Å and the quality of the observed 00ℓ diffraction patterns varied through the composition region where the structure crystallized. TEM cross sections confirm the interleaving of bilayers of PbSe with Se-Mo-Se trilayers. Measured resistivity values ranged over five orders of magnitude, from 0.307 Ωm to 70 μΩm, and Seebeck coefficients ranged from -181 μV/K to 91 μV/K in the samples after the initial annealing to form the basic structure. Annealing in an open system results in two distinctly different behaviors: a combined high conductivity / low Seebeck coefficient, as expected for a heavily doped semiconductor or metal, and a lower conductivity / higher Seebeck coefficient, as expected for a semiconductor. Annealing of samples under a controlled atmosphere of selenium resulted in low conductivities and large negative Seebeck coefficients, suggesting an n-doped semiconductor. STEM Z-contrast images revealed an interesting volume defect, where PbSe grew through a region where a layer of MoSe2 would be expected in the perfect structure. Further studies are required to correlate the density of these defects with the observed electrical properties.
Citation: Journal of Electronic Materials
Pub Type: Journals
chalcogenides, thin film deposition, electrical resistivity, Seebeck coefficient, X-ray diffraction, STEM Z-contrast imaging, turbostratic disorder