New subvalent bismuth telluroiodides incorporating Bi-2 layers: the crystal and electronic structure of Bi2TeI

Two new subvalent bismuth telluroiodides, Bi2TeI and Bi4TeI1.25, 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 Bi2TeI single crystals demonstrated that the compound crystallizes in the monoclinic system (space group C/2m) with the unit cell parameters a = 7.586(l) A, b = 4.380(l) angstrom, c = 17.741(3) angstrom, beta = 98.20 degrees. The layered crystal structure of Bi2TeI 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.