Hydrogen-induced lattice expansion in a (001)-oriented Mo/V superlattice

The hydrogen-induced lattice expansion in a Mo/V single-crystal superlattice (${\mathit{L}}_{\mathrm{V}}$/${\mathit{L}}_{\mathrm{Mo}}$=2 nm/2 nm) has been studied by x-ray diffraction in the temperature range 20–500 °C and hydrogen pressures ranging from 5–625 torr in a vacuum x-ray furnace. For temperatures between 350–500 °C, the lattice expansion Δ${\mathit{d}}_{\mathrm{V}}$/${\mathit{d}}_{\mathrm{V}}$ of the vanadium lattice in the growth direction of the superlattice was found to vary linearly with the hydrogen concentration, up to concentrations of H/V=0.5 (atomic ratio) with a slope of ${\mathit{k}}_{\mathit{s}}$=0.042(3). This value is almost a factor of 5 smaller than the bulk vanadium value of ${\mathit{k}}_{\mathit{b}}$=0.19(1). The reduced lattice expansion is shown to originate from the truncation of the in-plane stress components and the change in elastic response upon clamping. © 1996 The American Physical Society.