Ab initio description of oxygen vacancies in epitaxially strained $$\hbox {SrTiO}_{{3}}$$ at finite temperatures

Abstract

Epitaxially grown $$\hbox {SrTiO}_{{3}}$$ SrTiO 3 (STO) thin films are material enablers for a number of critical energy-conversion and information-storage technologies like electrochemical electrode coatings, solid oxide fuel cells and random access memories. Oxygen vacancies ($${\mathrm{V}_{{\mathrm{O}}}}$$ V O ), on the other hand, are key defects to understand and tailor many of the unique functionalities realized in oxide perovskite thin films. Here, we present a comprehensive and technically sound ab initio description of $${\mathrm{V}_{{\mathrm{O}}}}$$ V O in epitaxially strained (001) STO thin films. The novelty of our first-principles study lies in the incorporation of lattice thermal excitations on the formation energy and diffusion properties of $${\mathrm{V}_{{\mathrm{O}}}}$$ V O over wide epitaxial strain conditions ($$-4 \le \eta \le +4$$ - 4 ≤ η ≤ + 4 %). We found that thermal lattice excitations are necessary to obtain a satisfactory agreement between first-principles calculations and the available experimental data for the formation energy of $${\mathrm{V}_{{\mathrm{O}}}}$$ V O . Furthermore, it is shown that thermal lattice excitations noticeably affect the energy barriers for oxygen ion diffusion, which strongly depend on $$\eta $$ η and are significantly reduced (increased) under tensile (compressive) strain. The present work demonstrates that for a realistic theoretical description of oxygen vacancies in STO thin films is necessary to consider lattice thermal excitations, thus going beyond standard zero-temperature ab initio approaches.

Revealing Atomic‐Scale Ionic Stability and Transport around Grain Boundaries of Garnet Li7La3Zr2O12 Solid Electrolyte

“…These findings are well consistent with the observations in the studies on the oxides where the imposed tensile lattice strain can reduce the O vacancy formation energy. [56,57] Especially, at the coarse GBs in the models with 15% tensile strain, we have observed the negative values of E f of V O × , indicating the probable existence of O vacancy at the GB, which has also been reported in the recent experiment on the LLZO GB. [37] Figure 5.…”

Tuning the Electronic, Ion Transport, and Stability Properties of Li-rich Manganese-based Oxide Materials with Oxide Perovskite Coatings: A First-Principles Computational Study

“…Since the epitaxial strain introduced by the interface in the STO (LNMO) block is high and tensile (null), the corresponding out-of-plane dimension significantly shrinks in an attempt to conserve its original volume (barely changes), thus minimizing the accompanying elastic energy. 41 Epitaxial strain in a heterogeneous system requires the condition that atomic bonds bridging the distinct materials are formed at their interface. In the STO/LNMO system, we confirmed the presence of such bridging atomic bonds, involving Ti ions in the STO side and O ions in the LNMO side, through both charge density difference (CDD) (eq 2) and Bader charge analysis (Figure 2b).…”

“…44,45 For the calculation of vacancy formation energies, E V , we removed one single oxygen or lithium ion from the simulation supercell, which leads to defect concentrations of ∼0.4 and ∼ 1.6%, respectively. For the sake of computational affordability and in view of previous firstprinciples results reported on bulk STO, 41 in the present study, all point defects have been assumed to be neutrally charged; the formation energy of vacancies, E V , therefore, was estimated by using the formula:…”

“…The projector-augmented wave method (PAW) was employed to represent the ionic cores by considering the following electronic states as valence: Sr 4 s , 4 p , and 5 s ; Ti 3 p , 4 s , and 3 d ; O 2 s and 2 p ; Li 1 s , 2 s , and 2 p ; Mn 3 p , 4 s , and 3 d ; Ni 3 p , 4 s , and 3 d . A “Hubbard- U ” scheme was employed for a better treatment of the Ti, Mn, and Ni and 3 d electric orbitals, with a selected U value of 2.0, 3.9, and 6.0 eV, − respectively. An energy cutoff of 520 eV and a Monkhorst–Pack k -point grid of 2 × 2 × 1 for integrations within the Brillouin zone were used in the geometry optimizations, which led to total energies converged to within 1 meV per atom.…”

“…Li ions were simulated as interstitials in the STO block. Since oxygen vacancies are a common type of point defects in STO thin films, 41 we also simulated and analyzed the impact of V O on Li diffusion (i.e., by considering an oxygen vacancy density of ∼2% in an 80-atom STO supercell). The STO lattice parameters between layers A STO and B STO (Figure 2a) were adopted to simulate Li transport near the STO/LNMO interface (Figure 6, case "Li in STO near interface").…”