CRYSTAL-STRUCTURE AND TWINNING OF THE INT ERMETALLIC PHASE BETA-BI2RH

beta-Bi2Rh was prepared from the elements in the presence of iodine. A t room temperature the lattice constants of the triclinic centrosymmet ric structure are a = 6.743 (1), b = 7.030 (1), c = 7.067 (1) Angstrom , alpha = 104.76(1), beta = 100.73 (1), gamma = 105.79 (1)degrees. X-r ay investigations on a single crystal revealed that each Rh atom is su rrounded by seven Bi atoms in a monocapped trigonal prism. The prisms share common rectangular and trigonal faces to build infinite rows of double prisms, which are finally connected into parallel (100) layers. Twinning along [010] is commonly observed, indicating a pseudomono-cl inic C-centered cell.