Synthesis and characterization of turbostratically disordered (BiSe)_1.15TiSe₂

Abstract

The synthesis and characterization of turbostratically disordered (BiSe) 1.15 TiSe 2 is reported. Specular and in-plane x-ray diffraction studies indicate an alternating structure containing two planes of a distorted rock salt structured BiSe and a Se-Ti-Se trilayer of TiSe 2 with independent lattices. The title compound was found to be turbostratically (rotationally) disordered about the c-axis, and the BiSe layer displays an orthorhombic in-plane structure with a = 4.562(2) Å and b = 4.242(1) Å. Temperature dependent electrical resistivity reveals that the disordered compound is metallic, but with less temperature dependence than may be expected for a 3D crystal, which is attributed to the lack of coherent vibrations due to the turbostratic disorder. The room temperature resistivity was found to be ρ = 5.0 × 10 −6 m with a carrier concentration of n = 5 × 10 21 cm −3 . Comparing the carrier concentration to (PbSe) 1.16 TiSe 2 suggests that the bismuth is trivalent and donates an electron to the conduction band of the TiSe 2 constituent.

Misfit Layer Compounds and Ferecrystals: Model Systems for Thermoelectric Nanocomposites

“…Interestingly, the low residual in-plane resistivity ratio is not due to an increased resistivity at low temperatures, which may be expected from impurity or other fixed defect scattering. For systems where both thermodynamic and metastable compounds are reported, the resistivity at low temperatures is similar in magnitude [86,87,88,89]. Misfit layer compounds with high carrier concentrations show behavior expected for a metal, with resistivity increasing linearly with temperature due to increased electron-phonon scattering.…”

“…The metastable analogs, while showing similar magnitudes of resistivity below 50 K, do not show the increase at higher temperatures. This lack of temperature dependence has been attributed to the lack of electron-phonon scattering at higher temperatures [88,89]. In general, ferecrystals have a higher mobility than the misfit layer compounds.…”

“…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].…”

Structural and electrical properties of a new ([SnSe]1.16)1(NbSe2)1 polytype

“…There have been relatively few comparisons of misfit layer compounds and ferecrystals, but when investigated there have been significant differences between both the structures and the properties of different polytypes [12,13]. This prompted us to prepare the [(SnSe) 1.16 ] 1 (NbSe 2 ) 1 ferecrystal, and here we compare its structure and properties to the [(SnSe) 1.16 ] 1 (NbSe 2 ) 1 misfit layer compound.…”

Correlation of Reduced Interlayer Charge Transfer with Antiphase Boundary Formation in BixSn1–xSe–NbSe2 Heterostructures

“…Additionally, the rectangular distortion of the BiSe layers may be unrelated to the presence of antiphase boundaries. In (BiSe) 1.15 (TiSe 2 ) n compounds the BiSe in‐plane adopts an even larger rectangular distortion than that observed for (BiSe) 1.10 NbSe 2 , but there are only a few antiphase boundaries, and significant interlayer charge transfer occurs , . This suggests that relative band alignments may play a crucial role in determining the interlayer interaction that will occur.…”