Unique Periodic Modulations in the Infinite [Te_x]~(n-) Chains of RbUSb_0.33Te_6

摘要

The new phase RbUSb_0.33Te_6 is described. The structure of RbUSb_0.33Te_6 is acentric and trigonal (space group P3) with infinite [UTe_6]~(2-] columns running along the c axis. The structure has straight [UTe_6]~(6-) columns in which the U atoms adopt distorted tri-capped trigonal prisms. The central axis in the [UTe_6]~(2-) columns is defined by a row of U atoms 4.964 (1) A 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 wich is 9 times larger (a_super = a_sub, b_super = b_sub, c_super = 3c_sub) than that of the ideal P3 structure. The superstructure is caused y 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 approx S/cm.