Synthesis, Characterization, and Electrical Properties of ([SnSe]1+δ)m(NbSe2)3 Ferecrystalline Compounds
Ta, Phuong Kim
MetadataShow full item record
Ta, Phuong Kim
Ferecrystalline compounds ([SnSe]1+δ)m(NbSe2)3, or (m,3), with 1 < m < 30 were prepared using the modulated elemental reactants (MER) technique in a vacuum deposition chamber. A 5.78(4) Å change in c-lattice parameter change was observed as the compounds were systematically built up in thickness, ranging from 1 to 30 layers of m. The c-lattice constants for both SnSe and NbSe¬2 constituents found in the (m,3) compound were consistent with those of the previously studied (m,1) and (m,2) compounds. In-plane diffraction data revealed distortion of the basal plane as the thickness of the SnSe layer increased, similar to those of the (m,1) and (m,2). HAADF-STEM images showed turbostratic disorder, which is the signature feature of ferecrystals, and different polytypes of the NbSe2 subunits. Metallic behavior was observed in electrical resistivity. The slight upturn in the resistivity at low temperature in higher m value indicates carrier localization. Carrier concentration decreases as the number of SnSe layer increases, but it decreases faster than expected, suggesting charge is transferred from the SnSe constituent to the NbSe2 subunit. A change from a negative to positive slope as a function of temperature was observed in carrier mobility as m increases. When plotted as a function of m/n ratio, electrical resistivity of the (m,3) compounds deviates from the predicted parallel resistor model, indicating the middle NbSe2 layer has a limited influence on resistivity of the compounds.