Structural and electrical properties of (PbSe)_1·16TiSe₂

Abstract

The synthesis and characterization of a new layered compound with the composition (PbSe)1·16TiSe2 in thin-film form is reported in this study. The structure of the new compound was characterized by specular and in-plane synchrotron x-ray diffraction studies, which indicate that the compound can be described as a layered intergrowth of PbSe and TiSe2 in which the individual constituents are precisely layered yet rotationally (turbostratically) disordered with an average in-plane domain size in the order of 10 nm. In contrast to crystalline (PbSe)1·16(TiSe2)2 prepared by solid-state reaction at high temperature, the electrical resistivity in the range 20–300 K is nearly temperature independent. The Seebeck coefficient at room temperature was measured to be S = −66(1) μV/K at the carrier concentration of n = 2·1(5) × 1021 cm−3, indicating behavior characteristic of a heavily doped semiconductor. The electrical transport properties for the (PbSe)1·16TiSe2 compound are compared and contrasted to those of other misfi t-layered and turbostratically disordered (MX)1+δ(TX2)n compounds.

Misfit Layer Compounds and Ferecrystals: Model Systems for Thermoelectric Nanocomposites

“…The TiSe 2 a -axis lattice parameter was found to be between 0.3561(6) nm and 0.357(1) nm. These values are similar to those reported previously for PbSe-TiSe 2 ferecrystals and misfit layer compounds [65,86,92]. …”

“…As with the thermodynamically stable misfit compounds, however, materials based on TiSe 2 have shown to produce carrier concentrations on the order of 10 21 cm −3 , with high Seebeck coefficients and in-plane resistivity values on the order of 10 −5 Ωm. To date, (SnSe) 1.2 TiSe 2 , (PbSe) 1+δ (TiSe 2 ) n (n = 1, 2) and (BiSe) 1.15 TiSe 2 have all been reported [77,86,88,92]. For TiSe 2 based compounds, the only direct comparison between a ferecrystal and a misfit compound is for [(PbSe)] 1.16 (TiSe 2 ) 2 [65,86].…”

Carrier dilution in TiSe2 based intergrowth compounds for enhanced thermoelectric performance

“…1. 18,22 Extrapolating the trend in lattice parameter to n = 0 gives a value of 0.61(1) nm for the PbSe bilayer thickness, as seen in Fig. A systematic increase in the c-axis lattice parameter is apparent as n is increased, indicating the formation of a growing superstructure.…”

“…The m = 1, n = 1, 2 compounds have been previously reported in detail, 18,22 with a brief overview of all compounds with m, n r 3 also recently discussed. The m = 1, n = 1, 2 compounds have been previously reported in detail, 18,22 with a brief overview of all compounds with m, n r 3 also recently discussed.…”

Telluride Misfit Layer Compounds: [(PbTe)1.17]m(TiTe2)n

“…Briefly, an initial series of five precursors was made with m:n values targeted at m:n = 1:1, 1:3, 1:5, 5:1, and 3:1 by depositing a Pb-Te bilayer m times and a Ti-Te bilayer n times, assuming that d was the same as for the known selenide compound. [9] Based on the composition and thickness of these initial samples, the deposition parameters were iteratively adjusted to obtain the desired composition for each layer and to scale the individual layers to the correct thickness. The diffraction patterns of the optimized asdeposited samples suggest that some self-assembly occurred during the deposition process and the time for which the sample was kept at room temperature.…”