Structural quantum isotope effects in amorphous beryllium hydride

The structure factors for amorphous ${\mathrm{BeD}}_2$ and ${\mathrm{BeH}}_2$ were measured using synchrotron x-ray and neutron diffraction techniques. The results show that the structure of amorphous ${\mathrm{BeD}}_2$ is comprised of corner-sharing tetrahedra and is therefore analogous to amorphous ${\mathrm{H}}_2\mathrm{O}$ and ${\mathrm{BeF}}_2.$ A substantial increase in the height of the first sharp x-ray diffraction peak of ${\mathrm{BeD}}_2$ compared to ${\mathrm{BeH}}_2$ is interpreted as a marked increase in the extent of intermediate range order in ${\mathrm{BeD}}_2$ due to stronger network formation. A real-space comparison with liquid water, reveals that the structural isotopic quantum effects are quite different in the two hydrides.