HYDROGEN-INDUCED LATTICE EXPANSION OF VANADIUM IN A FE V(001) SINGLE-CRYSTAL SUPERLATTICE/

The hydrogen-induced lattice expansion of the vanadium layers in a Fe/ V (001) single crystal superlattice (L-Fe/L-V= 1.8/1.6 nm) was investi gated by x-ray diffraction. The expansion coefficient (k(s)) was found to be strongly dependent on the hydrogen concentration. At concentrat ions below 0.1 in average H/V (atomic ratio) it was determined to k(s) = 0.35(1), which is almost twice the coefficient for bulk vanadium. T he corresponding lattice parameter changes are six times those in the bulk material. This gigantic lattice expansion is inferred to be parti ally caused by the immediate population of the octahedral z sites in t he superlattice structure. At intermediate concentrations (0.1-0.3) th e expansion coefficient is approximately 0.10, and at the highest conc entrations it is even further reduced. The nonlinear behavior is assoc iated with the long range of the host-mediated elastic interaction and the local ordering of the dipolelike elastic distortion of the host l attice.