Danchuk V. Orientational order in pure cryocrystals and their solutions

THEED was used to study the structure and the rotational subsystem state of molecular cryocrystals of cubic symmetry, formed by linear symmetric molecules pure (p-D2, CO2), as well as binary alloys CO2 with atomic (Kr), and molecular (N2O) components. A new method of reconstruction from the structural analysis data of absolute values of orientational order parameter {ita} has been developed for molecular crystals of cubic system. The absolute value of ita for the ordered phase of p-D2 (xJ=1>90 %, Т=1.5 K) has been evaluated from neutron scattering data. The ita values are in a good agreement with the theoretical predictions. Analysis shows that a complete description of three rotational subsystem in solid CO2 requires two order parameters, ita2 and ita4, The temperature dependence of both have been reconstructed for temperatures between T = 5 K to T = 65 K from THEED data. The structure of CO2-Kr alloys was studied over the entire range of mutual concentrations. A cluster approach has been suggested to explain the concentration dependence of the lattice parameter of the Kr-diluted solutions in CO2. The parameters ita2 and ita4 for solid solutions CO2-Kr have reconstructed in the concentration range up to 38 mol.% Kr. The lattice parameter a of CO2-N2O alloys have been determined at 5 and 65 K for a large enough number of CO2 concentration x. A step-wise feature in the a(x) dependence has been observed, the "critical" concentration of the step being strongly influence by the deposition temperature.