Defect processes in Li2ZrO3: insights from atomistic modelling

Abstract

density functional theory (DFT) simulations in conjunction with experimental nuclear magnetic resonance (NMR) in order to investigate the Li ion migration mechanisms. Disorder in the anion sublattice can impact the material properties and the diffusion of point defects [14,15]. This is a common future in energy related materials where intrinsic disorder and doping can influence the formation (i.e. concentration of point defects mediating diffusion) and the migration (i.e. the energy barriers for diffusion) [16][17][18][19]. Controlling point defects such as vacancies is important for semiconductors, superconductors, and oxides [20][21][22][23][24][25][26][27][28]. A way to defect engineer the concentration and clustering of point defects in the anion sublattice (for example oxygen vacancies) is via the introduction of dopants. This is effectively to maintain charge balance in the lattice [29]. For example the introduction of two trivalent dopants in the tetravalent cerium site in CeO 2 can be charge balanced by the formation of an oxygen vacancy. Therefore the introduction of trivalent dopants in CeO 2 is an efficient way to form oxygen vacancies at concentrations higher than the equilibrium concentration [29].Atomistic simulation is an efficient and powerful way to understand the energetics of point defects in energy materials [30][31][32]. The main aim of the present study is to systematically investigate the intrinsic defect processes and impact of doping in Li 2 ZrO 3 using DFT. In particular, we consider here divalent (Mg, Zn, Ca, Cd, Sr, Ba), trivalent (Al, Ga, Sc, In, Y) and tetravalent (Si, Ge, Ti, Sn, Pb, Ce) substitutionals and their association with oxygen vacancies.Abstract Lithium zirconate (Li 2 ZrO 3 ) is an important material that is considered as an anode in lithium-ion batteries and as a nuclear reactor breeder material. The intrinsic defect processes and doping can impact its material properties. In the present study we employ density functional theory calculations to calculate the defect processes and doping in Li 2 ZrO 3 . Here we show that the lithium Frenkel is the dominant intrinsic defect process and that dopants substituting in the zirconium site strongly associate with oxygen vacancies. In particular, it is calculated that divalent dopants more strongly bind with oxygen vacancies, with trivalent dopants following in binding energies and even tetravalent dopands having significant binding energies. The results are discussed in view of the application of Li 2 ZrO 3 in energy applications.

Nonstoichiometry and Li‐ion transport in lithium zirconate: The role of oxygen vacancies

“…Kordatos et al calculated via DFT the binding energies between theses substitutional defects (i.e., ) and their nearest‐neighbor oxygen vacancies. This DFT study shows that the formation of oxygen vacancies when divalent and trivalent are incorporated into the Zr site in LZO are energetically favorable.…”

“…They also showed that the binding of dopant cations with oxygen vacancies becomes weaker from divalent to tetravalent cations. For example, dopant‐ binding is much weaker for tetravalent Ti dopant (~ −0.2 eV) than for trivalent Al/Ga dopant (~ −4 eV), and divalent Mg dopant has the strongest binding (~ −7 eV) . Based on Equations , 2 oxygen vacancies are created when a divalent iron ion replaces a tetravalent zirconium ion, and this number reduces to 1 for trivalent ions like Ga 3+ and Al 3+ , and to zero for tetravalent ions like Ti 4+ .…”

“…Cations including Nb, Ti, Ga, Fe, Al, and Mg were selected since they have ionic radii smaller than or close to that of 6-coordinated Zr 4+ (0.72 A), also their binding energies with oxygen vacancies are relatively high as calculated by Kordatos et al 15 In addition, Ce 4+ with 21% larger ionic radius was studied. The doping level for all was 0.1 per formula, and a 5 wt% extra Li was added to compensate the Li loss during synthesis and sintering.…”

“…For example, dopant-V ÁÁ o binding is much weaker for tetravalent Ti dopant (~À0.2 eV) than for trivalent Al/Ga dopant (~À4 eV), and divalent Mg dopant has the strongest binding (~À7 eV). 15 Based on Equations 3a-d, 2 oxygen vacancies are created when a divalent iron ion replaces a tetravalent zirconium ion, and this number reduces to 1 for trivalent ions like Ga 3+ and Al 3+ , and to zero for tetravalent ions like Ti 4+ . This can readily explain the rise of oxygen vacancies with lowering valence number of dopants shown in Figure 8B.…”

“…According to DFT calculations by Kordatos et al, the dopants will strongly bind with the nearest‐neighbor oxygen vacancies. Oxygen vacancies induced by cation doping or lithium loss will have an impact on the Li + diffusion in LZO.…”