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

The hydrogen-induced lattice expansion in a Mo/V single-crystal superlattice (L(V)/L(Mo)=2 nm/2 nm) has been studied by x-ray diffraction in the temperature range 20-500 degrees C and hydrogen pressures ranging from 5-625 torr in a vacuum x-ray furnace. For temperatures between 350-500 degrees C, the lattice expansion Delta d(V)/d(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 k(s)=0.042(3). This value is almost a factor of 5 smaller than the bulk vanadium value of k(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.