High-pressure phases of lithium borohydride LiBH${}_{4}$: A first-principles study

High-pressure phases of lithium borohydride LiBH $_{4}$ : A first-principles study

Yansun Yao and Dennis D. Klug

Phys. Rev. B 86, 064107 – Published 15 August 2012

Abstract

High-pressure phase transformations in LiBH $_{4}$ were theoretically investigated using first-principles density functional methods. A series of pressure-induced structural transformations are predicted in LiBH $_{4}$ , as Pnma (phase II) → $I$ 4 $_{1}$ /acd (phase III) → NaCl type (phase V) → NiAs type (phase VI) → polymeric forms. The calculated pressures for the II → III transition and the III → V transition are 0.9 and 27 GPa, respectively, and both agree very well with recent experimental observations. A B1-B8 transformation becomes more favored at higher pressure, and this results in a distorted NiAs structure of LiBH $_{4}$ . Denoted as phase VI, the distorted NiAs structure is the lowest enthalpy phase of LiBH $_{4}$ above 60 GPa and confirmed to be dynamically stable by phonon calculations. The ionic character and band gap of the phase VI decreases with increasing pressure. At still higher pressures, the extended structures formed by polymeric BH $_{4}$ layers intercalated by Li $^{δ +}$ cations may exist, and these represent the metallic forms of LiBH $_{4}$ .