A study of the chlorine nuclear quadrupole resonance frequency spectrum in potassium hexachloro-osmate by Fourier transform methods

A study of the chlorine nuclear quadrupole resonance spectrum of K2OsCl6 in the vicinity of the structural phase transition using Fourier transform techniques is reported. At high temperatures a single symmetric line spectrum is observed as expected from the high temperature cubic antifluorite structure. Below Tc = 45 K the two symmetric line spectrum characteristic of a tetragonal distortion is seen. At intermediate temperatures, 45 < T < 150 K the spectrum consists of a single asymmetric line. A detailed analysis reveals that for the single crystal sample the asymmetric line is composed of two symmetric components, a main line, and a weak satellite shifted −1.5 kHz relative to the main line. This feature is unaffected by changes in temperature near Tc. It is attributed to the influence of interstitial impurities on neighbouring chlorine ions. For the powder sample, the asymmetry is qualitatively different. A detailed analysis shows that the line is a superposition of three components. In addition to the two components present in the single crystal, a third, broad component develops as the temperature approaches Tc. This feature of the spectrum is the cluster induced order-disorder manifestation of the local dynamics. The most probable reason that this third component is not observed in the single crystal spectrum is because it is too broad due to a difference in the detailed dynamics of the two samples.