Dynamical properties and temperature induced molecular disordering of LiBH4 and LiBD4

We report on neutron powder-diffraction experiments, inelastic incoherent neutron-scattering experiments, and density-functional calculations on dynamics, order and disorder properties of LiBH4 and LiBD4. From refinement of LiBD4 structure at 10 and 302 K, we found an almost ideal tetrahedral geometry of BD4 ions (difference between shortest and longest interatomic distances is less than 4% for B-D bond, and less than 3% for D-D bond), close to the calculated geometry. A quantitative agreement was found between experimental and calculated anisotropic temperature factors of individual atoms. For phonon energies