| Popis: |
Neutron time-of-flight powder-diffraction spectra have been obtained in potassium cyanide (KCN) at temperatures between 25 and 200 K and at pressures between 35 and 366 MPa. These data sample five different phases of KCN. In phase [ital C], which exists at 366 MPa and below 170 K, the structure is determined to be paraelectric with the monoclinic space-group symmetry [ital C]2/[ital c]. This is in disagreement with a previous study, which determined the structure to be ferroelectric with space-group symmetry [ital Cc]. In phase [ital D], which exists at 366 MPa and below 120 K, the structure is determined to be paraelectric with the monoclinic space-group symmetry [ital C]2/[ital m]. The cyanide ions lie in mirror planes. In both phases [ital C] and [ital D], the cyanide ions are ordered with respect to the direction of their bonds but disordered with respect to interchange of C and N. Also in these phases, line broadening due to an inhomogeneous shear strain was observed. A mathematical treatment of this phenomenon is given. |
