New Fast Oxygen Ion Conductor Perrierite-Type Oxide La₄Mn₅Si₄O_22+δ Discovered by Harnessing the Materials Project and High-Throughput Computation

Oxygen-ion conducting materials are important for a variety of applications such as solid-oxide fuel cells, gas sensors, catalysts, and oxygen separation membranes. Applications typically utilize oxygen-active materials operating at high temperatures (e.g. ≈800 °C for fuel cells). The key issue that limited industrial applicability is the high operating temperature which results in high system cost, materials degradation, and slow start-up and shutdown cycles. Development of alternative electrolyte/electrodes materials with good oxygen ionic conductivity at low temperature (room temperature-400 °C) is of great interest. However, fast oxygen conductor materials are concentrated in only a handful of materials structure families such as perovskite, fluorite, manganite, melilite, scheelite, and apatite. Hence, it is critical to find new materials which transport oxygen ion efficiently at low temperatures.<br/>In this work, we developed a high-throughput computational screening of the 33,975 oxide materials from the Materials Project database and discovered the new structure family of interstitial oxygen diffuser based on perrierite-type oxide La₄Mn₅Si₄O₂₂ (LMSO). We used a hierarchy of screening criteria including the geometric free space, thermodynamic stability, synthesizability, redox-active elements, diffusion pathways, ab initio calculated defect formation energy and diffusion barrier. Our screening has yielded several material families to date, among which LMSO was selected for investigation with higher-level DFT hybrid functional calculations and experimental ionic conductivity measurements. Interstitial oxygen formation energy and migration energy were studied by Density Function Theory (DFT) calculations with SCAN functional. The formation energy of interstitial oxygen is -0.11 eV at a concentration of 2.3% under air condition, indicating that LMSO is oxygen hyperstoichiometric with an expected composition of La₄Mn₅Si₄O_22+0.5 in air. Oxygen ion diffusion pathways and energetics were studied by ab initio Molecular Dynamic (AIMD) simulation, showing migration pathways along the connected sorosilicate Si₂O₇ groups through an interstitial mechanism. The migration barrier is predicted as 0.45 eV and 0.69 eV based on AIMD simulation and the Climbing Image-Nudged Elastic Band (CI-NEB) calculation, respectively. The diffusivity of oxygen ion is calculated to be 10^-5 cm²/s and the ionic conductivity is 0.1 S/cm at 800 °C. The above computational predictions have been verified by experimental investigations. The existence of interstitial oxygen (δ ~ + 0.5) is validated by the Electron Probe Micro-analyzer (EPMA) and iodometric titration method, and the ionic conductivity is measured as 0.11 S/cm at 800 °C, consistent with the computational results. Experimental studies show that LMSO has mixed electronic and oxygen ionic conduction, indicating that LMSO is a very promising oxygen active material for numerous applications.