Phase Diagram of System (Bi2Te3)-(BiI3)and Crystal Structure of BiTeI

The phase diagram of the pseudobinary system (Bi 2 Te 3 )–(BiI 3 ) has been determined by the methods of differential thermal analysis, X-ray diffraction, X-ray microanalysis and optical microscopy. It was found that there existed a single phase compound around the non-stoichiometric composition Bi 1.00 Te 0.98 I 1.02 which had the melting point of 560°C. The range of the single phase composition seemed to be from Bi 0.99 Te 0.94 I 1.07 to Bi 1.00 Te 0.99 I 1.01 BiTeI has a phase transition which occurs at about 470°C and the crystal structure in the low temperature phase is hexagonal; a =4.346 Å, c =6.835 Å. The atomic distances of Bi–Te, Te–I and I–Bi are 3.826 Å, 3.235 Å and 5.532 Å, respectively. If the difference between the atoms Te and I is ignored, the structure of the compound may be similar to that of CdI 2 . The compound is revealed to be semi-metallic in nature by measuring its electrical resistivity and Hall coefficient.