PHASE-DIAGRAMS OF TLI-BI3 (B=AS,BI) AND SOME PROPERTIES OF THE NEW COMPOUND TL7BI3I16

In the system TlI-AsI3 we find no ternary halide. The phase diagram Tl I-BiI3 shows the two stable compounds Tl3Bi2I9 and Tl7Bi3I. Twinning p revents a full determination of the structures. Large single crystals of Tl7Bi3I are obtained by the Bridgman technique. By sensitive piezoe lectric and electrooptic measurements the absence of a center of symme try is demonstrated; however, the effects are strongly quenched by the structural twinning. The electronic properties are similar to those o f BiI3. A direct band gap at about 2.2 eV is accompanied by two indire ct transitions at slightly smaller photon energies. Copyright (C) 1997 Elsevier Science Ltd.