Rare gas binary alloys are suitable objects for investigation into basics of solid state [1]. A unique feature of regular diluted solutions of noble gases is the possibility of experimentally determining the excess volume per impurity, which can be compared with the conclusions of various microscopic theories [2]. A successful theoretical description of the equilibrium properties of mixed crystalline systems is based on several generally accepted postulates, in particular, Vegard’s empirical rule, dealing with the lattice parameters. However, in reality, the morphology and structure of cryoalloys strongly depends on the procedure for growing the samples [3].
The transmission high energy electron diffraction (THEED) technique was employed for studying the structure of the regular diluted solid Ar - Kr solutions. The polycrystalline samples of regular diluted solid Ar - Kr solutions (to 15 mol.% of one of the components) were prepared in situ by deposition of a precooled gaseous mixture onto an Al and carbon substrates cooled to 20 K. The lattice parameters of solutions were measured.
To explain the experimentally observed structural anomalies in diluted solid Ar - Kr solutions, we calculated the positions of atoms in a nine-layer spherical cluster of krypton with an argon atom in the center and argon cluster with krypton atom in center. The interaction was approximated with the Lenard–Jones potential. The substitution volumes vAr of an argon atom in the krypton crystal and vKr a krypton atom in argon crystal were calculated. It was shown that compared to the generally accepted estimates obtained within the nearest-neighbor approximation, the value of vAr is approximately twice as small. This effect is explained by an additional repulsion of the first coordination sphere of krypton atoms arising as the krypton atoms approach each other upon their inward motion. As for the reverse situation (a krypton atom in the argon cluster), in which the guest particle is larger than the regular one, the experimental and calculated results correlate with the estimates obtained from simple combinatorial considerations.
References
- Rare Gas Solids, M.L. Klein and J.A. Venables (eds.), Academic Press, London, (1976) vol. 1; (1977) vol. 2.
- M. A. Strzhemechny, A. I. Prokhvatilov, and L. D. Yantsevich, Physica B 198, 267 (1994).
- V. V. Danchuk, A. A. Solodovnik, N. S. Mysko, and M. A. Strzhemechny, Fiz. Nizk. Temp. 41, 546 (2015) [Low Temp. Phys. 41, 424 (2015)].
