Structural isotopic effect of the alpha/beta phase transition in vanadium hydride and its influence on the equilibrium coefficient of separation of hydrogen isotopes in the gas-solid system
Ep. Magomedbekov et Av. Bochkarev, Structural isotopic effect of the alpha/beta phase transition in vanadium hydride and its influence on the equilibrium coefficient of separation of hydrogen isotopes in the gas-solid system, RUSS J PH C, 73(11), 1999, pp. 1732-1736
The equilibrium separation coefficient for hydrogen isotopes (alpha(H-D)) i
n the vanadium dihydride VHn(s, n approximate to 0.7)-H-2(g) system was mea
sured by equilibration in a circulation unit and laser desorption at 298, 3
73, and 473 g. The alpha(H-D) distribution coefficients determined by the t
wo methods were in close agreement with each other. The literature neutron
diffraction data were used to calculate the isotopic ratios of the reduced
partition functions and alpha(H-D) for the alpha' and beta' phases of the V
2H and V2D hydrides by direct summation over vibrational energy levels. The
calculated isotopic effects (both structural isotopic effects in phase dia
grams and the separation coefficient for hydrogen isotopes) were fairly clo
se to the experimental values. This result substantiates the suggestion tha
t the reason for the unusual behavior of the separation coefficient for hyd
rogen isotopes and for the difference in the crystal structures of vanadium
hydride and its deuterated analogue is a combination of a strongly anharmo
nic potential in octahedral lattice sites and a small difference in the ene
rgies of coordination of hydrogen atoms in tetrahedral and octahedral sites
.