Structural quantum isotope effects in amorphous beryllium hydride

The structure factors for amorphous BeD₂ and BeH₂ were measured using synchrotron x-ray and neutron diffraction techniques. The results show that the structure of amorphous BeD₂ is comprised of corner-sharing tetrahedra and is therefore analogous to amorphous H₂O and BeF₂. A substantial increase in the height of the first sharp x-ray diffraction peak of BeD₂ compared to BeH₂ is interpreted as a marked increase in the extent of intermediate range order in BeD₂ 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.