New subvalent bismuth telluroiodides incorporating Bi2 layers: the crystal and electronic structure of Bi2TeI

Abstract

Two new subvalent bismuth telluroiodides, Bi 2 TeI and Bi 4 TeI 1.25 , were prepared by the gas phase synthesis. The compositions of these phases were determined by energy dispersive X ray spectroscopy. X ray diffraction study of melt grown Bi 2 TeI single crystals demonstrated that the compound crystallizes in the monoclinic system (space group C/2m) with the unit cell parameters a = 7.586(1) Å, b = 4.380(1) Å, c = 17.741(3) Å, β = 98.20°. The layered crystal structure of Bi 2 TeI consists of weakly bonded two dimensional blocks with a stoichiometry of the title compound. The blocks are stacked along the c axis. Each block consists of eight atomic layers alternating in the Te-Bi-I-Bi-Bi-I-Bi-Te order and includes a double layer of bismuth atoms. Based on the results of ab initio quantum chemical calculations, the title compound is expected to possess a pronounced anisotropy of conductivity.Key words: low dimensional phases, layered compounds, main group metal-metal bond ing, bismuth telluroiodides.Bismuth is one of a few p metals, which can form crystalline compounds containing extended metal-metal bond systems. For example, the crystal structures of subvalent iodides and mixed subvalent iodide bromides Bi 4 I 4-n Br n 6 consist of one dimensional fragments, which can be de scribed as corrugated bismuth strips of width 4, 14, or 18 atoms, respectively, which are bounded on both sides by halogen atoms. The geometry of these strips is very similar to the atomic arrangement in the crystal structure of bismuth metal. In addition, two dimensional electro neutral Bi 2 layers, which also retain the structure of bis muth metal, were found in the crystals of subvalent bis muth selenides 7-9 and tellurides. 7,10,11The structures of subvalent bismuth chalcogenides, for example, with compositions BiQ and Bi 4 Q 3 (Q = Se, Te), can be considered as a result of intercalation of Bi 2 layers into the crystal structures of layered se lenides and tellurides with composition Bi 2 Q 3 formed by weakly bonded two dimensional electroneutral Bi 2 Q 3 blocks.The aim of the present study was to intercalate bis muth double layers into the crystal structure of bismuth telluroiodide BiTeI. This compound crystallizes in the hexagonal system 12 (space group P3m1, a = 4.3302(1) Å, c = 6.854(1) Å) and can be described as a distorted 2H CdI 2 type crystal structure, in which the tellurium and iodine atoms in the anion sublattice are completely ordered so that the tellurium atoms replace one layer of iodine atoms in the starting CdI 2 structure (Fig. 1).The shortest Bi-Te and Bi-I bonding distances (3.039 and 3.272 Å, respectively) and the Te-I non bonded distance (3.93 Å) suggest a layered character of the structure. Since the geometry of the Bi-Te and Bi-I bond systems in BiTeI (Te-Bi-Te and I-Te-I angles are 83° and 91°, respectively) is similar to that of the Bi-Bi bond system in the Bi 2 layer of subvalent bismuth tellurides (in BiTe 11 and Bi 4 Te 3 , 11 the Bi-Bi distances are 3.267 and 3.098 Å, and the Bi-Bi-Bi angles are 85°a nd 91°, re...

Minimum Thermal Conductivity in Weak Topological Insulators with Bismuth‐Based Stack Structure

“…Bi 2 TeI belongs to the Z 2 (0; 001) class and has a crystal structure of alternately stacked by QSH layers (Bi bilayers) and NI layers (BiTeI bilayers), as shown in Figure a. Weak bonding between the adjacent BiTeI monolayers also exists in the NI layers, which is presumably due to the opposite dipole moment in the two adjacent layers due to the stacking arrangement of the BiTeI bilayers. The dipole moment in the BiTeI compound is unidirectional and is essential in generating the giant Rashba effect .…”

Synthesis, Crystal and Topological Electronic Structures of New Bismuth Tellurohalides Bi2TeBr and Bi3TeBr

“…51 Crystal-growth routes 52 and phase relations in the pseudo-binary BiBr 3 -Bi 2 Te 3 section 53,54 have been studied in full detail. In contrast to that, syntheses of Bi 2 TeI 32,33 and Bi 3 TeI 33 were reported quite recently. We have applied the following core principles, that were determined previously for the Bi-Te-I system, 33 to the present study of the Bi-Te-Br system: 1.…”

“…The crystal structure can be described, just like Bi The crystal structure of Bi 2 TeI was initially solved in the C-centered monoclinic cell. 32 We showed 33 a possible transformation into a cell with trigonal (rhombohedral) metrics. This transformation causes negligible deviations of angles (<0.01°) and atomic positions (< 0.1 pm) from the higher symmetric space group R3 ത m 33 .…”

Bismuth‐based candidates for topological insulators: Chemistry beyond Bi2Te3

“…The band structure calculations in scalar-relativistic approximation [63] predict the compound to be a strongly anisotropic metallic conductor in-plane and a semiconductor with a gap of about 0.2 eV (LDA) in the stacking direction. Moreover, crystal growth experiments complemented with X-ray powder diffraction studies and energy-dispersive X-ray spectroscopy have confirmed the existence of compounds with higher bismuth contents up to "Bi 4 TeI 1.25 " [56,63] [64] suggesting that more than one [Bi 2 ] layers per unit cell could be incorporated in the parent BiTeI structure. It is likely that the sequence of layers could be disordered or modulated structures have formed by the high-temperature route of synthesis.…”