EXCESS IMPURITY VOLUMES IN BINARY-MIXTURES OF CRYOSOLIDS

We present a survey of molar volumes for binary cryocrystal alloys, of which one component is a heavier rare gas (Ar, Kr or Xe) and the other, one of the simplest molecules (N2, CO, O2, CO2, CD4, CH4). The low-concentration data (obtained with powder X-ray and transition electron diffraction methods) are used to calculate REVI (relative excess volume per impurity) values. For a linear molecular heavy impurity in atomic matrices, we present a quasistatic theory. The behavior of the REVI with temperature and content (at low enough impurity fractions) is qualitatively explained with account of the anisotropic forces between molecular species and the vanishing of these forces upon introduction of substitutional impurities. The relevant anisotropic potentials between unlike species are mostly derived in the atom-atom approximation from Lennard-Jones potentials.