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 investigated by x-ray diffraction. The expansion coefficient (k(s)) was found to be strongly dependent on the hydrogen concentration. At concentrations 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. The corresponding lattice parameter changes are six times those in the bulk material. This gigantic lattice expansion is inferred to be partially caused by the immediate population of the octahedral z sites in the superlattice structure. At intermediate concentrations (0.1-0.3) the expansion coefficient is approximately 0.10, and at the highest concentrations it is even further reduced. The nonlinear behavior is associated with the long range of the host-mediated elastic interaction and the local ordering of the dipolelike elastic distortion of the host lattice.