Van Vleck paramagnetism of the thulium garnet Tm3Al5O12 Original Research Article

For inspection of thermal behaviors of sodium (Na) atom in the bulk and on the surface of two layered hydrogen terminated cluster model, 2C150H30, the molecular dynamics calculation was taken place at molecular mechanics 2 level. From the requirement of structural optimization, interlayer distance of 2C150H30 is 3.38 Å which is consistent with the observed value. In the cluster models intercalated and adsorbed by one Na atom, C150H30·Na·C150H30 and Na·2C150H30, respectively, the Na atom is stabilized beneath and above the nearest central carbon atom, C0, in the upper layer where the distances, Na–C0, are 2.76 and 3.16 Å, respectively. Adsorption of the Na atom to the surface has no influence on the geometrical structure of cluster model, whereas, intercalation to two layers expands the interlayer distance maximally to 5.01 Å which will be responsible for the carbon expansion of graphite electrode in cryolite melt-alumina slurries. Diffusion processes are observed above 200 K for the Na atoms stabilized in both sites. Although the Na atom migrates parallel to the layers in the range between 200 and 300 K in C150H30·Na·C150H30, it moves above the carbon layer from the center to the circumference periodically below 250 K and gets out at 300 K for Na·2C150H30. The migration rates of Na atom are almost the same irrespective of the diffusion areas.