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

Abstract

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 \ifmmode^\circ\else\textdegree\fi{}C and hydrogen pressures ranging from 5--625 torr in a vacuum x-ray furnace. For temperatures between 350--500 \ifmmode^\circ\else\textdegree\fi{}C, the lattice expansion \ensuremath{\Delta}${\mathit{d}}_{\mathrm{V}}$/${\mathit{d}}_{\mathrm{V}}$ 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. \textcopyright{} 1996 The American Physical Society.