Synthesis of [(SnSe)_1.16–1.09]₁[(Nb_xMo_1–x)Se₂]₁ Ferecrystal Alloys

Abstract

Modification of the modulated elemental reactant method allowed the first reported synthesis of quaternary [(MX) z ] m [(T x T′1–x )­X2] n compounds with controlled compositions. Metastable ferecrystal compounds, [(SnSe)1.16–1.09]1[(Nb x Mo1–x )­Se2]1 with x = 0, 0.26, 0.49, 0.83, and 1, were synthesized and characterized by X-ray diffraction, electron probe microanalysis (EPMA), and scanning transmission electron microscopy (STEM). Misfit layer dichalcogenide analogues, showing controlled alloying of the dichalcogenide layers, have not been reported. Changes in lattice parameters, as a function of x, were similar to literature observations for the (Nb x Mo1–x )­Se2 system. The c-lattice parameters of the ferecrystal alloys decreased linearly from 12.53(2) Å for [(SnSe)1.09]1(MoSe2)1 to 12.27(2) Å for [(SnSe)1.16]1(NbSe2)1. The a-lattice parameters of the dichalcogenide constituent increased from 3.329(8) Å for [(SnSe)1.09]1(MoSe2)1 to 3.461(4) Å for [(SnSe)1.16]1(NbSe2)1. The a-lattice parameter of the rocksalt constituent remained constant resulting in a linear increase in misfit parameter with increased Nb content. Temperature dependent electrical resistivity measurements showed a transition from semiconducting to metallic behavior as the Nb content of the alloys increased.

Effect of sulfur substitution on the thermoelectric properties of (SnSe)1.16NbSe2: charge transfer in a misfit layered structure

“…In this study, we present an in-depth account of the high temperature thermoelectric properties of (SnSe) 1.16 NbSe 2 or Sn 1.16 NbSe 3.16 mist selenide. This compound has been studied by a few authors in the past for various aspects, such as, (1) its complex crystal structure 27 which ensures low lattice thermal conductive like all other mist layered chalcogenides, (2) synthesis and study of ferecrystalline alloys/thin lms [28][29][30] which have shown that charge transfer and hence the electronic properties in this mist are tunable and, (3) polycrystalline room temperature electronic properties 16,27 which indicate its low room temperature electrical resistivity ($6 mU m). These previous studies make this mist selenium compound a suitable candidate for thermoelectric investigation as well.…”

Self-assembly of designed precursors: A route to crystallographically aligned new materials with controlled nanoarchitecture

“…The thickness of each block can be individually controlled as well as the order of the layers, resulting in over 20,000 distinct nanoarchitectures for n and m less than 10. [36] The three constituents can also be combined into one heterostructure, either by alloying the constituents that have a common structure [37], to form a random (A,B)C alloy, or by preparing three component heterostructures with distinct layers of each constituent forming an ordered ABAC alloy. These two possibilities provide access to a large number of new compounds, many more than one would like to make, so the challenge is to understand how properties change as the constituent thicknesses, order, and composition are varied to accelerate the search for the optimum properties for a particular application.…”

“…[37] The composition control is accomplished via calibrations similar to what was discussed earlier. There are at least two different approaches based on the number of sources used.…”

“…The synthesis and properties of [(TiTe 2 ) 1 + δ ] x [(Bi 2-x Sb x ) 2 Te 3 ] y alloys was reported by Mortensen et al, [98] the rock salt constituent was alloyed in ([Pb x Sn 1-x ]Se) z TiSe 2 , [ 99] and the transition metal constituent was alloyed in (SnSe) z (Nb x Mo 1-x )Se 2 . [37] ORDERED ABCB ALLOYS Ordered A m B n C p or more complex sequences of three compounds, such as A m B n C p B q , where A, B and C are compounds containing three compositionally different constituents, three structurally different constituents or a mix of these can be prepared expanding the calibration procedure described above. If the calibrated deposition parameters for two component systems containing the constituents are known, the process is straight forward.…”

Tetragonal tungsten bronzes Nb8−xW9+xO47−δ: optimization strategies and transport properties of a new n-type thermoelectric oxide

“…1,[19][20][21] Still, many experimental efforts failed because the small grains also reduced the power factor S 2 /r. in misfit-layered materials [26][27][28][29][30][31][32] or materials with crystallographic shear (CS) planes. 22 Therefore, materials containing inherent phonon scattering centers at the atomic level have attracted scientific attention recently.…”