Synthesis and Structures of Ternary Chalcogenides of Aluminum and Gallium with Stacking Faults: KMQ2 (M=Al, Ga; Q=Se, Te)

A new oxychloride, BiSeO3Cl, is obtained at 300°C from a mixture of BiOCl and SeO2 as large colorless crystals. Roomtemperature single-crystal X-ray investigation combined with an SHG test point to a noncentrosymmetric structure (space group P212121, a=6.353(2), b=7.978(3), c=8.651(4) ?, Z=4, RF=5.60%). The structure is characterized by a three-dimensional framework which is built up of BiO5Cl2 pentagonal bipyramids and trigonal pyramids of SeO3E (E is the lone electron pair of Se(IV)). The dielectric and optical nonlinear properties of BiSeO3Cl are evaluated.