First-principles studies of phase stability and crystal structures in Li-Zn mixed-metal borohydrides

Abstract

We address the problem of finding mixed metal borohydrides with favorable thermodynamics and illustrate the approach using the example of LiZn 2 (BH 4 ) 5 . Using density functional theory (DFT), along with the grand canonical linear programming method (GCLP), we examine the experimentally and computationally proposed crystal structures and the finite-temperature thermodynamics of dehydrogenation for the quaternary hydride LiZn 2 (BH 4 ) 5 . We find the following: (i) For LiZn 2 (BH 4 ) 5 , DFT calculations of the experimental crystal structures reveal that the structure from the neutron diffraction experiments of Ravnsbaek et al. is more stable [by 24 kJ/(mol f.u.)] than that based on a previous X-ray study. (ii) Our DFT calculations show that when using the neutron-diffraction structure of

Thermodynamic stability of transition metals on the Mg-terminatedMgB2(0001) surface and their effects on hydrogen dissociation and diffusion

“…• C) as well as reversibility [9] triggered extensive research on hydrogen release and decomposition pathways of complex metal hydrides [3,[10][11][12]. In particular, two complex hydrides systems attracted intense interest: 1) The first involves Mg(BH 4 ) 2 , which contains 14.9%…”

Colossal and Reversible Barocaloric Effect in Phase Change Materials n-Alkanes

“…The lattice constants and ion positions are optimized using the Broyden-Fletcher-Goldfarb-Shanno (BFGS) quasi-Newton algorithm with the force convergence criterion less than 10 −3 eV/Å. The vibrational entropy is calculated using vib = , where ω is the vibrational frequency, q the wave vector, and v the index of the phonon mode 46 . Here we should point out that we calculated the phonon and vibrational entropy with ignoring the thermal expansion effect, since the calculations incorporating the thermal expansion effect would require the third-order force constants, which is quite time-consuming for the C 18 H 38 supercell.…”

“…10) with pressure present a high consistency with the experiment results 26,27 This indicates the rationality of the relevant models and parameters adopted in the present MD simulation. The previous studies definitely indicate that DFT is highly reliable in estimating the lattice vibration entropy (Svib) of crystalline materials 46 . Therefore, the Svib of C18H38 in solid state was estimated by this mean and compared with the total entropy (St) obtained by experiments.…”

Metal Borohydrides beyond Groups I and II: A Review

“…A first-principle study (DFT + PEGS (prototype electrostatic ground state)) indicated that LiZn(BH 4 ) 3 would have a triclinic C1 space group symmetry [ 146 ]. LiZn(BH 4 ) 3 is calculated to be more stable (about −8 kJ/mol cation) as compared to the parent borohydrides of Li and Zn [ 146 ], but unstable towards decomposition to LiBH 4 and LiZn 2 (BH 4 ) 5 (from DFT along with grand canonical linear programming method) [ 158 ]. In turn, LiZn 2 (BH 4 ) 5 is calculated to decompose in a rather complex pathway [ 158 ]: LiZn 2 (BH 4 ) 5 → 2Zn + 1/5 LiBH 4 + 2/5 Li 2 B 12 H 12 + 36/5 H 2 → 2Zn + 1/6 LiH + 5/12 Li 2 B 12 H 12 + 89/12 H 2 → 11/6 Zn + 1/6 LiZn + 5/12 Li 2 B 12 H 12 + 15/2 H 2 → Zn + 5B + LiZn + 10H 2 …”