THE STRUCTURE AND THE ORIENTATIONAL ORDER-PARAMETER OF AR-CO2 SOLID-SOLUTIONS

Electron diffraction studies of the structural characteristics of Ar-C O2 solid solutions are carried out over the entire range of their mutu al concentrations. The regions of low concentrations of both component s are analyzed in detail and the relative excess volumes Delta upsilon /upsilon are determined for the CO2 impurity in solid Ar (Delta upsilo n/upsilon similar or equal to 0.8), and for the Ar impurity in solid C O2 (Delta upsilon/upsilon similar or equal to 0.28). The experimental results and relationships are compared with the results obtained from the semi-quantitative theory on the basis of known atom-atom potential s. An expression relating the intensity of superstructural reflections I-(super) (including the reflection 210) with the long-range orientat ional order parameter eta is obtained. It is found that I(210)proporti onal to eta(2) to a high degree of precision. The experimental depende nce of the orientational order parameter eta on the argon concentratio n in solutions rich in CO2 is obtained. (C) 1998 American Institute of Physics. [S1063-777X(98)01209-2].