Unique periodic modulations in the infinite [Te_x]^n-chains of RbUSB_0.33Te₆

The new phase RbUSb_0.33Te₆ is described. The structure of RbUSb_0.33Te₆ is acentric and trigonal (space group P3) with infinite [UTe₆]^2- columns running along the c axis. The structure has straight [UTe₆]^6- columns in which the U atoms adopt distorted tri-capped trigonal prisms. The central axis in the [UTe₆]^2- columns is defined by a row of U atoms 4.064 (1) apart, i.e., a metal "wire" seethed with what appear to be three infinite zig-zag Te chains. The crystals, however, exhibit a super-structure that results in a rhombohedral space group which is 9 times larger (a_super = √3a_sub, b_super = √3b_sub, c_super = 3c_sub) than that of the ideal P3 structure. The superstructure is caused by a periodic modulation of Te - Te distances in the zig-zag chains. The almost equal Te - Te distances in the infinite chains are in fact dimers, trimers, and pentamers. The material is a narrow gap semiconductor with a room temperature electrical conductivity of ∼ 40 S/cm.