Mobile Vacancies Research Articles

On a drift‐diffusion model for perovskite solar cells

AbstractWe introduce a vacancy‐assisted charge transport model for perovskite solar cells. This instationary drift‐diffusion system describes the motion of electrons, holes, and ionic vacancies and takes into account Fermi–Dirac statistics for electrons and holes and the Fermi–Dirac integral of order for the mobile ionic vacancies in the perovskite. The free energy functional we work with corresponds to that choice of the statistical relations. To verify the existence of weak solutions, we consider a problem with regularized state equations and reaction terms on any arbitrarily chosen finite time interval. We motivate its solvability by time discretization and passage to the time‐continuous limit. A priori estimates for the chemical potentials that are independent of the regularization level ensure the existence of solutions to the original problem. These types of estimates rely on Moser iteration techniques and can also be obtained for solutions to the original problem.

Enhancing Thermochemical Energy Storage Performance of Perovskite with Sodium Ion Incorporation

Perovskite materials are promising for thermochemical energy storage due to their ability to undergo redox cycling over a wide temperature range. Although BaCoO3 exhibits excellent air cycling properties, its heat storage capacity in air remains suboptimal. This study introduces Na into the lattice structure to enhance oxygen vacancy formation and mobility. DFT+U simulations of the surface structure of Na-doped BaCoO3−δ indicate that incorporating Na improves surface stability and facilitates the formation of surface oxygen vacancies. NaxBa1−xCoO3−δ compounds were synthesized using a modified sol–gel method, and their properties were investigated. The experimental results demonstrate that Na doping significantly enhances the redox activity of the material. The heat storage capacity increased by above 50%, with the Na0.0625Ba0.9375CoO3−δ solid solution achieving a heat storage density of up to 341.7 kJ/kg. XPS analysis reveals that Na doping increases the concentration of surface defect oxygen, leading to more active oxygen release sites at high temperatures. This enhancement in redox activity aligns with DFT predictions. During high-temperature cycling, the distribution of Na within the material becomes more uniform, and no performance degradation is observed after 300 cycles. Even after 450 cycles, Na0.0625Ba0.9375CoO3−δ retains over 96% of its initial redox activity, significantly outperforming fresh BaCoO3−δ. These findings elucidate the mechanism by which Na doping enhances the thermochemical heat storage performance of BaCoO3−δ and provide new insights for the design of perovskite-based materials.

Controlled assembly and synthesis of oxygen-deficient W18O49 films based on solvent molecular strategy for electrochromic energy storage smart windows

18O49 is a promising electrochromic material with abundant oxygen vacancy and high carrier mobility. However, the electrochromism of W18O49 is not satisfactory, the regulation and synthesis of high-performance W18O49 have become the research hotspot. In this work, it is found that the main chain and side chain structure of solvent molecules can control the assembly and synthesis of W18O49 film, so as to achieve excellent electrochemical and electrochromic properties. The porous reticular W18O49 film synthesized in short-chain molecular solvent shows the excellent transmittance modulation (81.6 % at 633 nm, 77.0 % at 1050 nm), and exhibits the high energy storage of 41.7 mF cm−2 at 0.1 mA cm−2. Solvent molecular strategy provides a new way for the synthesis and regulation of W18O49 electrochromic films and promotes the further development of high-performance electrochromic materials.

In situ observation of reversible phase transitions in Gd-doped ceria driven by electron beam irradiation

Ceria-based oxides are widely utilized in diverse energy-related applications, with attractive functionalities arising from a defective structure due to the formation of mobile oxygen vacancies (VO⋅⋅\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${V}_{O}^{\\cdot \\cdot }$$\\end{document}). Notwithstanding its significance, behaviors of the defective structure and VO⋅⋅\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${V}_{O}^{\\cdot \\cdot }$$\\end{document} in response to external stimuli remain incompletely explored. Taking the Gd-doped ceria (Ce0.88Gd0.12O2-δ) as a model system and leveraging state-of-the-art transmission electron microscopy techniques, reversible phase transitions associated with massive VO⋅⋅\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${V}_{O}^{\\cdot \\cdot }$$\\end{document} rearrangement are stimulated and visualized in situ with sub-Å resolution. Electron dose rate is identified as a pivotal factor in modulating the phase transition, and both the VO⋅⋅\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${V}_{O}^{\\cdot \\cdot }$$\\end{document} concentration and the orientation of the newly formed phase can be altered via electron beam. Our results provide indispensable insights for understanding and refining the microscopic pathways of phase transition as well as defect engineering, and could be applied to other similar functional oxides.

Polaron assisted hopping mechanism in microwave processed Nd doped second layered aurivillius SrBi2Nb2O9 ceramics

The polycrystalline Sr0.8Sn0.2Bi1.75Nd0.25Nb2O9 (NdSBN) was synthesized using the green synthesis microwave sintering method, which significantly reduced the processing parameters of the NdSBN ceramics. Orthorhombic crystal structure with A21am symmetry was revealed by Rietveld refinement study, whereas the doping-induced strain and crystallite size was studied using the Williamson Hall method. Crossectional SEM micrographs confirm the plate-like structure, with an average grain size of 273.7 nm. A diffuse type of phase transition was observed at 345 °C, which usually arises due to compositional fluctuations and mobile oxygen vacancies; further, the diffusiveness of the NdSBN was studied using Uchino and Nomura function, a modified version of Curie-Weiss law (CW). The frequency and temperature-dependent dielectric study of NdSBN ceramics display a Maxwell-Wagner relaxation with a high loss in a low frequency regime, possibly due to the presence of leakage current in the solid solution. Frequency dependent AC conductivity obeys Jonscher's power law, whereas DC conductivity supports polaron assisted hopping in NdSBN composition with dual activation energies of 0.55 eV and 0.75 eV, which correspond to electrons and ions, respectively. The non-Debye type relaxation mechanism in conjunction with negative temperature coefficient of resistance (NTCR) behavior was demonstrated by temperature dependent impedance spectroscopy, while modulus spectroscopy confirmed the multiple relaxation processes in NdSBN ceramics.

CsPbI3 Perovskite Quantum Dot-Based WORM Memory Device with Intrinsic Ternary States.

The migration of mobile ionic halide vacancies is usually considered detrimental to the performance and stability of perovskite optoelectronic devices. Taking advantage of this intrinsic feature, we fabricated a CsPbI3 perovskite quantum dot (PQD)-based write-once-read-many-times (WORM) memory device with a simple sandwich structure that demonstrates intrinsic ternary states with a high ON/OFF ratio of 103:102:1 and a long retention time of 104 s. Through electrochemical impedance spectroscopy, we proved that the resistive switching is achieved by the migration of mobile iodine vacancies (VIs) under an electric field to form conductive filaments (CFs). Using in situ conductive atomic force microscopy, we further revealed that the multilevel property arises from the different activation energies for VIs to migrate at grain boundaries and grain interiors, resulting in two distinct pathways for CFs to grow. Our work highlights the potential of CsPbI3 PQD-based WORM devices, showcasing intrinsic multilevel properties achieved in a simple device structure by rationally controlling the drift of ionic defects.

The dependence on displacement rate and temperature of near-surface void-denuding in self-ion irradiated pure polycrystalline and single-crystal iron

Pure iron has been irradiated with Fe2+ ions in a series of studies to identify neutron-atypical physical processes that influence the depth dependence of void swelling, focusing especially on suppression effects arising from injected interstitials and surface proximity. One paper in this series examined the surface influence in single-crystal Fe irradiated to 50 and 100 peak dpa over a range of temperature (425–525 °C) and ion energy (1.0, 2.5, 3.5, 5.0 MeV) while keeping the peak damage rate at 1.2 × 10–3 dpa/s, although the surface dpa rate was lower but increasing with decreasing ion energy, providing a small range of surface dpa rate. The observed denuded width Δx was modified to incorporate sputtering loss. The activation energy governing the denuding process was found to be EΔx4=1.65±0.03eV, higher than the vacancy migration energy EVm known to be 0.67 eV. This difference was attributed to the effect of dissolved carbon (103 appm) which reduces the effective vacancy mobility and thereby increases the effective migration energy.Since the previous study involved a factor of only 2.83 in near-surface dpa rate it is important to confirm that the dependence of EΔx4 on dpa rate is maintained over a larger range of damage rates. In this study polycrystalline Fe with 140 appm carbon was irradiated with 5 MeV Fe2+ ions to 50, 100 and 150 dpa over a range of peak dpa rates (2.0 × 10–4, 1.2 × 10–3, 6.0 × 10–3 dpa/sec) and temperatures (425, 475, 525 °C). At very high dpa levels sputtering and void growth lead to loss of voids via shrinkage, limiting the upper dose level where this technique can be applied. It was found that the single-crystal and polycrystal specimens yielded essentially identical behavior with EΔx4 = 1.65 eV, validating the application of this activation energy over a wider range of dpa, dpa rate, temperature, and crystal form.

Vacancy Suppression and Resonant Level Rendering Extraordinary Power Factor in Sn0.99In0.01Te/Tourmaline Composite.

SnTe, as a potential medium-temperature thermoelectric material, reaches a maximum power factor (PF)usually above 750K, which is not conducive to continuous high-power output in practical applications. In this study, PF is maintained at high values between 18.5 and 25µWcm-1K-2 for Sn0.99In0.01Te-xwt% tourmaline samples within the temperature range of 323 to 873K, driving the highest PFeng of 1.2Wm-1K-1 and PFave of 22.5µWcm-1K-2, over 2.5 times that of pristine SnTe. Such an extraordinary PF is attributed to the synergy of resonant levels and Sn vacancy suppression. Specifically, the Seebeck coefficient increases dramatically, reaching 88µVK-1 at room temperature. Meanwhile, by Sn vacancy suppression, carrier concentration, and mobility are optimized to ≈1019cm-3 and 740cm2V-1s-1, respectively. With the tourmaline compositing, Sn vacancies are further suppressed and the thermal conductivity simultaneously decreases, with the minimum lattice thermal conductivity of 0.9W m-1 K-1. Finally, the zT value ≈0.8 is obtained in the Sn0.99In0.01Te sample. The peak of the power output density reaches 0.89W cm-2 at a temperature difference of 600K. Such SnTe alloys with high and "temperature-independent" PF will offer an option for realizing high output power in thermoelectric devices.

Contrasting irradiation behavior of dual phases in Ti-6Al-4V alloy at low-temperature due to ω-phase precursors in β-phase matrix

Aiming to simulate the radiation damage effect on a dual α+β phase Ti-6Al-4V alloy utilized as high-intensity accelerator beam window material, a series of irradiation experiments were conducted with a 2.8 MeV-Fe2+ ion beam in several dpa regions at room temperature. The nano-indentation hardness increased steeply at 1 dpa and unchanged up to 10 dpa, due to the saturation of defect clusters and tangled dislocations in the dominant α-phase matrix with a size of 2–3 nm and a density of about 1×1023 m−3. In contrast in the intergranular β-phase, larger loops of 20–30 nm diameter were observed with much less density of about 5×1020 m−3. The diffraction pattern showed rectilinear diffuse streaks between the β-phase reflections, corresponding to the ω-phase precursor, without dose dependency in its intensity. FFT/I-FFT analysis of the HREM revealed a sub-nanometer-sized lattice disorder with local fluctuations, not discrete but continuous, and homogeneously distributed within the matrix β-phase stably against the irradiation. The significantly low dislocation density and the absence of phase transformation in the β-phase matrix could be attributed either to the strong sink effect expected for this distinctive sub-nanometer-sized homogeneous lattice disorder or to the anomalous point defect recombination induced by the high mobility of vacancies, both of which are originated from the metastable ω-phase precursors specifically formed in the β(BCC) phase of group-4 transition metals.

Nonvolatile resistive switching in interface-dominated memristors utilizing two-dimensional Cs2Pb(SCN)2Br2 perovskite films

In this study, all-inorganic two-dimensional (2D) perovskite Cs2Pb(SCN)2Br2 was employed in a thin-film vertical structure prototype memristor. The device consisted of a Cs2Pb(SCN)2Br2 film prepared through solution approach, sandwiched between an Ag electrode and a TiO2/FTO substrate bottom electrode. Two types of resistive switching (RS) behaviors were observed within a single device at different temperatures. At room temperature, the dominant control mechanism was the interface Schottky barrier, whereas at higher temperatures, the primary driving force shifted to the conductive channel. The device has an on/off ratio exceeding 103 under the interface control mechanism. The migration of mobile bromine vacancies within the Cs2Pb(SCN)2Br2 film, whose concentration was enhanced by the infiltration and reaction of the Ag active electrode within the Cs2Pb(SCN)2Br2 film, is proposed to be the root cause for both types of RS characteristics. These findings offer insights into the potential application of 2D Cs2Pb(SCN)2Br2 perovskite in RS memory devices.

The role of stacking fault tetrahedra on void swelling in irradiated copper

A long-standing and critical issue in the field of irradiated structural materials is that void swelling is significantly higher in face-centered cubic-structured (fcc) materials (1% dpa−1) as compared to that of body-centered cubic-structured (bcc) materials (0.2% dpa−1). Despite extensive research in this area, the underlying mechanism of the difference in swelling resistance between these two types of materials is not yet fully understood. Here, by combining atomistic simulations and STEM imaging, we find stacking fault tetrahedra (SFTs) are the primary cause of the high swelling rate in pure fcc copper. We reveal that SFTs in fcc copper are not neutral sinks, different from the conventional knowledge. On the contrary, they are highly biased compared to other types of sinks because of the SFT-point defect interaction mechanism. SFTs show strong absorption of mobile self-interstitial atoms (SIAs) from the faces and vertices, and weak absorption of mobile vacancies from the edges. We compare the predicted swelling rates with experimental findings under varying conditions, demonstrating the distinct contributions of each type of sink. These findings will contribute to understanding the swelling of irradiated structural materials, which may facilitate the design of materials with high swelling resistance.

Ion transport induced room-temperature insulator-metal transition in single-crystalline Cu2Se.

Cu2Se is a superionic conductor above 414 K, with ionic conductivities reaching that of molten salts. The superionic behavior results from hopping Cu ions between different crystallographic sites within the Se scaffold. However, the properties of Cu2Se below 414 K are far less known due to experimental limitations imposed by the bulk or polycrystalline samples that have been available so far. Here, we report the synthesis of ultra-thin, large-area single crystalline Cu2Se samples using a chemical vapor deposition method. The as-synthesized Cu2Se crystals exhibit optically and electrically detectable and controllable robust phases at room temperature and above. We demonstrate that Cu ion vacancies can be manipulated to induce an insulator-metal transition, which exhibits 6 orders of magnitude change in the electrical resistance of two terminal devices, accompanied by an optical change in the phase configuration. Our experiments show that the high mobility of the liquid-like Cu ion vacancies in Cu2Se causes macroscopic ordering in the Cu vacancies. Consequently, phase distribution over the crystals is not dictated by the diffusive motion of the ions but by the local energy minima formed due to the phase transition. As a result, long-range vacancy ordering of the crystal below 414 K becomes optically observable at a micrometer scale. This work demonstrates that Cu2Se could be a prototypical system where long-range ordering properties can be studied via electrical and optical methods.

Influence of aluminium doping on high purity quartz glass properties.

High purity natural quartz is used as raw material for the manufacture of quartz glass crucibles for solar-grade silicon ingots production. One key challenge for cost-effective ingot pulling is to maximise the ability of the crucible to withstand the process conditions (i.e., silicon load and temperature about 1500 °C) without deformation. In order to improve this glass property, aluminium was coated into the raw quartz materials. Our results showed that an addition of up to 1000 wt ppm Al substantially reduces deformation of glass and improves viscosity at high temperatures. This is likely due to the reduction of stability of OH groups in the quartz glass as well as a trapping effect of aluminium on oxygen vacancies. This hypothesis is also supported by atomistic models. In the presence of Al, formation energies of silanol groups (Si-O-H) were much higher than without. Furthermore, the presence of Al in the structure significantly reduces mobility of the oxygen vacancies. It was also found that formation of oxygen vacancies hinders cristobalite crystallisation, on the other hand, Al atoms themselves induce local weakening of the Si-O bond which accelerates the kinetics of the reconstructive phase transition from glassy state to crystalline phase. This was also confirmed experimentally in our study.

Effect of MnO2 addition on structure, electrical and optical properties of Ba(Fe0.5Nb0.5)O3 ceramics

Admixture of Ba(Fe0.5Nb0.5)O3 (BFN) ceramics with different content of MnO2 (0, 0.5, 1.0, 1.5 and 2.0 wt.%) powder were processed through conventional solid-state reaction route. The XRD characterization of all sintered samples confirmed the formation of a single cubic perovskite structure.MnO2 acts as sintering aid, which significantly enhances grain size of the BFN ceramics. The room temperature dielectric constant and conductivity of the MnO2 modified BFN ceramics were suppressed compared to the pure BFN ceramics. However, the dielectric constant increases with the increase in temperature above 250 ?C. The relaxation activation energy (>0.6 eV) and high dielectric constant (?104 at temperature above 250 ?C) of the MnO2 modified BFN ceramics were explained on the basis of ionization of oxygen vacancies, mobile oxygen vacancies and polaron hopping between multiple oxidation states of manganese (Mn2+ and Mn3+). A narrow band gap of 1.45 eV was observed in the 1.5 wt.% MnO2 modified BFN ceramics.

Effect of h-BN on corrosion behavior of nickel-copper alloy coatings prepared by high-speed laser cladding

Nickel-copper alloy is widely used because of its strong corrosion resistance in marine environment. There are great potentials to prepare NiCu alloy coatings on the surface of structural steel to replace cast NiCu alloys due to its high cost. High-speed laser cladding has characteristics of fast melting rate, low surface roughness, fine microstructure and low dilution ratio. However, nickel alloy coatings has the problem of solidification cracks. In this study, a series of composite coatings were prepared by using NiCu powders with different h-BN contents, then the effect of h-BN on structure and anti-corrosion of coatings was analyzed. The study shows that the structure of the NiCu composite alloy coatings was equiaxed crystals, columnar crystals and planar crystals from top to bottom portion. After adding h-BN, the coating had a lower oxygen vacancy mobility rate, resulted in the optimal corrosion resistance of passive film.

Microstructural evolution of compositionally complex solid-solution alloys under in-situ dual-beam irradiation

This work attempts to link the microstructural evolution of single-phase compositionally complex alloy (CCA) compositions under dual-beam irradiation to their Mn-content via the stacking-fault energy (SFE) and vacancy migration energies. Two alloys, Cr18Fe27Mn27Ni28 and Cr15Fe35Mn15Ni35, along with less compositionally complex pure Ni and Fe56Ni44 binary were irradiated at 500 and 600 °C under dual-beam 1 MeV Kr2+ and 16 keV He+ heavy-ions up to 7 displacements per atom (dpa) with a He/dpa ratio of 0.75 %/dpa using in situ transmission electron microscopy (TEM). Due to the bubble-stabilizing effect of implanted He, bubbles were observed in all irradiations, and populations of faulted interstitial loops were characterized in Cr18Fe27Mn27Ni28 and Cr15Fe35Mn15Ni35. A reduction in swelling was observed in the two CCAs compared to pure Ni and Fe56Ni44. Although swelling increased from 500 to 600 °C in Fe56Ni44, Cr15Fe35Mn15Ni35 and Cr18Fe27Mn27Ni28 both swelled slightly more at 500 °C. This was attributed to the difference in vacancy mobility, stronger pinning effect of vacancies on He, and the sink strength of faulted dislocation loops. Faulted interstitial loops nucleated with a higher number density and dislocation line density in Cr15Fe35Mn15Ni35 at both temperatures, and at 600 °C in both materials. The differences in faulted loop population and temperature effect on swelling are correlated to the Mn-content and the measured SFE (20.2 ± 6.7 mJ/m2 for Cr18Fe27Mn27Ni28 and 9.2 ± 3.4 mJ/m2 for Cr15Fe35Mn15Ni35).

Refreshing Industrially Processed 6xxx Series Aluminum Alloys after Prolonged Natural Aging

Natural aging (NA) undesirably hardens 6xxx series aluminum alloys and hampers subsequent paint‐bake (PB) hardening, thus limiting the use of material after prolonged storage. It is presented that a refreshment treatment for seconds at a temperature between 230 and 290 °C can effectively lower the hardness/strength of two commercial alloys that have experienced NA for ≈3.5 years and enhance their PB hardening, thus enabling the reuse of the material with minimal energy input. The treatment is based on dissolving solute clusters formed during prior aging, but precipitation during refreshment can compromise its efficacy. The dependence of cluster dissolution and precipitation on the refreshment parameters as well as on the alloy composition is analyzed. A higher temperature is suggested for refreshing AA6014 alloy than for AA6016 alloy due to a higher thermal stability of the clusters in the former. Natural secondary aging (NSA) is investigated and it is proposed that the remaining undissolved clusters play an important role in controlling the mobile vacancy concentration. Refreshment experiments utilizing various heating media demonstrate that the treatment is hardly sensitive to the heating rate which facilitates its industrial implementation. The refreshed alloy can undergo further preaging to enhance the NSA stability and PB hardening.

Effect of isosymmetric phase transition in MIEC perovskite on the kinetic parameters of its interaction with oxygen

Oxygen partial pressure relaxation technique was used to study transient kinetics of re-equilibration in the reaction of nonstoichiometric oxide Ba0.5Sr0.5Co0.75Fe0.2Mo0.05O3-δ with oxygen within a region of 3-δ stoichiometry close to the nominal oxidation state 3+ for cobalt where an isosymmetric phase transition cubic perovskite P1 – cubic perovskite P2 is observed. The relaxation data were analyzed using a macrokinetic model that explicitly takes into account the power-law dependence of the surface reaction rate on the oxygen partial pressure. A twofold decrease in the power-law exponent (n = 0.7 to n = 0.3) was found at the point of the P1-P2 phase transition, which indicates a change in the mechanism of the rate-determining step of the reaction caused by the transition. At the same time, the functional dependence of the diffusion mobility of oxygen vacancies on the equilibrium oxygen pressure does not change at the transition point, which means that the transition does not affect the mechanism of bulk vacancy mobility.

Laser-modulated formation of conduction path for the achievement of ultra-low switching voltage in resistive random-access memory (RRAM)

Energy saving is one of critical issues that must be seriously considered for the development of next-generation memory devices. In this study, an ultralow-power resistive random-access memory (RRAM) device is fabricated through use of a successful modulation of the AlOX layer by a laser treatment optimized for the energy saving in resistive switching (RS). The device shows not only multilevel memory properties but also a high on/off ratio (∼106), good endurance (300 cycles), and excellent retention (>104 s). Most importantly, the laser-modulated device achieves ultra-low set and reset voltages (0.06 V and −0.04 V), leading to a very low-power consumption. It was observed that the amorphous phase in the AlOX layer is transformed into the polycrystalline phase and a concentration gradient of oxygen vacancies is secured. The grain boundaries in the polycrystalline act as pathways to facilitate the movement of oxygen vacancies. Meanwhile, the concentration gradient accelerates the diffusion mobility of the oxygen vacancies. The highly potential application of the laser-modulation to the flexible RRAM devices has been demonstrated by a strong level of RS performance maintenance from a device fabricated using the polyethylene terephthalate (PET) substrate.

Discovery of New Fast Oxygen Conductors: Bi2MO4x (M= rare earth, X= halogen) Via Unsupervised Machine Learning

Discovering new fast oxygen conductors is critical for developing many technologies, e.g., solid oxide fuel cells (SOFCs), solid oxide electrolysis cells (SOECs), proton ceramic fuel cells (PCFCs), and solid oxide air batteries, particularly for operation at lower temperatures (below 700 ˚C). By leveraging unsupervised machine learning techniques and large databases of computed materials data (e.g., Materials Project), we are able to rapidly explore and screen for new materials with high oxygen mobility. In this work, we used unsupervised machine learning analysis applied to features extracted from the structure of materials and discovered a new structural class of vacancy-mediated oxygen conductor. To do this, we applied the K-nearest neighbor (k-NN) algorithm on all the approximately 62,000 oxygen-containing compounds in the Materials Project database, using X-ray diffraction (XRD) and pair distribution function (PDF) data to represent the structural features. The neighbors of reference known for good oxygen conductors were screened with criteria relating to material stability, synthesizability, and electronic property dissimilarity (to ensure a novel material) compared to the reference material. Starting with the best-known oxygen conductor, the fluorite-type material, we examined the materials list of its nearest neighbors and identified the Bi2MO4X (M=Rare-earth element, X= halogen element) structural family as a novel group of fast oxygen conductors. In particular, Bi2LaO4Cl is a layered bismuth oxyhalide crystallized in the space group P4/mmm, adopting a “triple fluorite” layer [Bi2LaO4]+, balanced by the anion Cl- layer. The stability and mobility of oxygen vacancy in Bi2LaO4Cl were studied using Density Functional Theory (DFT) methods. 2+ oxygen vacancy is the most thermodynamically favorable defect type. Ab initio and machine learning-trained interatomic potential molecular dynamic simulations were performed to study the high temperature oxygen mobility in Bi2LaO4Cl. The simulation results show that Bi2LaO4Cl presents an extremely low migration barrier of 0.14 +/- 0.03 eV below 700 ˚C, suggesting 10 to 20 times higher ionic conductivity compared to yttria-stabilized zirconia (YSZ). Bi2LaO4Cl is an insulator with a wide band gap of 2.65 eV, indicating that Bi2LaO4Cl may be a promising electrolyte material with high oxygen ion conductivity and low electronic conductivity. This work demonstrates the power of combining unsupervised machine learning approaches with large materials databases for finding new fast oxygen conductors.