(a) Structure of I41/amd Mg(BH4)2. (b) Phonon dispersion curve of I41/amd Mg(BH4)2 at 5 GPa. (c) Structure of Fddd Mg(BH4)2. (d) Phonon dispersion curve of Fddd Mg(BH4)2 at ambient pressure.
Enthalpy difference curves of P6122 (α-phase), P42 nm, Fddd, P-3m1, I41/amd, and F222 structures. The F222 structure is the predicted ground state of Mg(BH4)2. 12 The inset at the bottom shows the calculated volume collapse from α-phase (P6122) to δ-phase (Fddd), and then to ɛ-phase (P-3m1), respectively.
Simulated X-ray diffraction spectrum (λ = 0.36814 Å) for (a) I41/acd and (b) Fddd Mg(BH4)2 at ambient pressure.
Simulated neutron diffraction spectrum (λ = 1.00000 Å) of (a) I41/acd and (b) Fddd Mg(BH4)2 at ambient pressure. The different peaks in intensity or peak position between (a) and (b) have been labeled by orange up triangles.
Calculated (solid symbols) and experimental (open square symbols) Raman active phonon frequencies of P-3m1 structure (ɛ-phase) as functions of pressure. The open stars represent the Raman peaks not belonging to ɛ-phase, although they were observed in experiment. The inset shows the structure of P-3m1 Mg(BH4)2.
Bond angle and bond length of Fddd ((a) and (b)) and P-3m1 Mg(BH4)2 ((c) and (d)) as a function of pressure.
Lattice parameters (in unit of Å) and atom positions (fractional coordinates) of Fddd structure at 6 GPa and P-3m1 structure at 10 GPa, respectively.
Calculated Raman frequency and its fitted pressure derivative (dv/dp) of P-3m1 Mg(BH4)2, which are compared with experimental data 17 during compression and decompression.
Bulk modulus (B 0 in GPa), its pressure derivative (B ′) and volume (V0) of Fddd Mg(BH4)2 at ambient pressure obtained from fitting Birch-Murnaghan equation of state, which are compared with Exp. 1. 18
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