X-Ray, infrared, and magnetic studies of α- and β-ruthenium trichloride

Abstract

Physical measurements have been made on samples of α- and β-RuCl₃ of relatively high purity. From X-ray powder patterns, the existence of a superstructure has been detected in α-RuCl₃, and the structure of β-RuCl₃ has been found to be of the β-TiCl₃ type with linear chains of ruthenium atoms lying in distorted octahedra of chlorine atoms. The infrared spectra have been obtained down to 70 cm.^–1; the nine bands observed for β-RuCl₃ indicate that the space group is the trigonal P3c1 (C³_3v), which means that there are–RuCl₃–RuCl₃–RuCl₃–units in the chains. There is a strong band attributed to a Ru–Cl stretching vibration at the relatively high frequency of 376 cm.^–1. The magnetic susceptibilities, obtained from 8 to 740°K for α-RuCl₃, and from 8 to 560°K for β-RuCl₃, show that α-RuCl₃ is antiferromagnetic below 13°K, and β-RuCl₃ below ca. 600°K, but in neither case has the antiferromagnetism been detected by neutron diffraction. The temperature dependence of the susceptibilities has been compared with the predictions of crystal field theory for α-RuCl₃, and with the theory of linear Heisenberg chains for β-RuCl₃.