A combined deep inelastic neutron scattering and ab initio lattice dynamics study of the hydride anion dynamics and bonding in La₂LiHO₃ oxyhydride

Abstract

Kobayashi et al (6279) (Science 2016, 351) reported recently the existence of pure Hconductivity in the oxyhydride La 2−x−y Sr x+y LiH 1−x+y O 3−y , while demonstrating its functionality through a prototype solid-state Ti/La 2 LiHO 3 /TiH 2 battery. In this study, we probe the atomistic motion of La 2 LiHO 3 obtained by the promising halide salt flux method, via a combination of deep inelastic neutron scattering (DINS) and ab initio lattice dynamics (LD) calculations verified by vibrational inelastic neutron spectroscopy (INS). We successfully describe the measured momentum distributions from DINS via our LD calculations, without observing any diffusion activation over the temperature range reported by Kobayashi et al. This observation is corroborated by model predictions from our LD study, which reveals that the hydride anions remain bound within a 3D-harmonic potential. We conclude that with the current synthesis parameters, the method produces a vacancy free lattice, and that a necessary ingredient for diffusive motion of His the presence of a large population of vacancies. Based on the harmonic prediction for the hydrogen kinetic energy, we derive a picture of the evolution of the effective bonding potential for the hydride anions, and link this to the dynamics associated with decomposition of the oxyhydride.

Defect Chemistry and Hydrogen Transport in La/Sr-Based Oxyhydrides

“…Either way, because half of all planar anion sites in LLHO are occupied by O atoms [Figure a], high-energy V O species must be involved in hydride diffusion. The high associated energy barriers will limit ionic conductivity, as previous studies have observed. , …”

“…The high associated energy barriers will limit ionic conductivity, as previous studies have observed. 21,36 SLHO, in contrast to LLHO, has a favorable structure for hydride conduction because all of the planar octahedral sites are occupied by H and the migration barrier for V H + is low. As outlined in Figure 3, O H − serves as a compensating acceptor for three different species depending on chemical potential: for very O-poor conditions, H O + , and at higher oxygen chemical potentials either V H + or H i + , depending on the hydrogen chemical potential.…”

Vibrational Motions Make Significant Contributions to Sequential Methyl C–H Activations in an Organometallic Complex

“…The complex in question is particularly suited to this technique as the deuteration process serves to provide a contrast measurement, allowing direct experimental distinction of modes belonging to the Cp* subunit. INS was therefore used to obtain a complete set of vibrational bands for both H 15 Cp*Rh–Cl and D 15 Cp*Rh–Cl which were then assigned using density functional theory phonon calculations. − DFT methods are well established in studies of the reactivity of metal complexes and metalloenzymes. , Validation of a particular DFT model through comparison to INS results has an added layer of rigor as it validates the local energy landscape of the model within the harmonic approximation. These validated DFT models then allowed us to demonstrate for the first time that vibrational energies and the motions of individual atoms can play crucial roles in the overall reaction profile for methyl activation.…”

Improving Hydride Conductivity in Layered Perovskites via Crystal Engineering

“…Additionally, Fjellvåg et al 15 have studied the La 2 LiHO 3 member of that series and found hydride mobility within the perovskite layer to be more facile than in the rock salt layer, which they link to La-O covalency, and that vacancies promote hydride diffusion. 16 In 2019 Takeiri et al 17 reported the high-pressure synthesis of Ba 2 ScHO 3 and observed hydride conduction at 300 • C. This compound also adopts the n = 1 RP structure but differs from previous examples in that the hydrides are distributed over the "apical" points of the octahedra and so reside in the rock salt layer, as indicated in Figure 1(d). This difference can be explained by straightforward electrostatic considerations, whereby the most positively charged cations coordinate to the most negatively charged cations.…”