Compositionally complex perovskite oxides: Discovering a new class of solid electrolytes with interface-enabled conductivity improvements

•Discovered compositionally complex perovskite oxides (CCPOs) as solid electrolytes•Compositionally designs can outperform conventional doping•Demonstrated grain-boundary-enabled conductivity improvements The recent emergence of high-entropy ceramics and a broader class (CCCs) unlocks vast compositional spaces for materials discovery. This study proposes demonstrates strategies tailoring CCCs via combination non-equimolar control interfaces microstructures to discover new electrolytes. Consequently, with enhanced ionic are unearthed. Notably, this discovers improvements, where processing utilized alter interfacial structures improve properties. Promising applications in all-solid-state batteries envisioned. More generally, these discovery be discover, design, tailor range energy storage many other applications. Compositionally (CCCs), including ceramics, offer vast, unexplored space Herein, we propose demonstrate grain boundaries (GBs) microstructures. 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LSTZ-derived We revealed phase-microstructure-property relationship enable us state-of-the-art baseline, yet comparable stability. addition, showed segregation profile underlying mechanisms, aberration-corrected advanced microscopy atomistic simulations active learning moment tensor (MTP) density functional theory (DFT) calculations employed. highlights significance controls boosting conductivities, addition designs, points direction design potentially CCCs. study, synthesized 28 CCPOs (through high-energy ball milling sintering 1,300°C 12 h air; see experimental procedures) key results three series Sn-containing (Li,Sr)(Ta,Nb,Zr,Sn)O3-δ (LSTNZS) two Hf-containing (Li,Sr)(Ta,Nb,Zr,Hf)O3-δ (LSTNZH) summarized supplemental information (Tables S1–S3). δ non-stoichiometry perovskites. comparison state-of-art attained GBs microstructures, while maintaining Figure 1 presents outline several generations generation, best LSTNZS CCPO (Li0.375Sr0.4375)(Ta0.334Nb0.347Zr0.211Sn0.108)O3-δ shows >2.3× baseline; compromised due presence redox-active (Figure S1). second (and Sn-free) LSTNZH slightly improvement baseline), 0.256 mS/cm 270% quenching. notable observed quenching primarily increase specific (true) (Note S1),42Haile S.M. Staneff Ryu K.H. Non-stoichiometry, boundary chemical proton perovskites.J. 36: 1149-1160https://doi.org/10.1023/A:1004877708871Crossref (297) resulting changes structure, (AC) scanning transmission electron (STEM) presented discussed subsequent section. 2A displays schematic unit cell (A-site-centered view). atomic-resolution high-angle annular dark-field (HAADF) STEM image representative 2B X-ray diffraction (XRD) pattern 2D, confirmed cubic structure. Next, discuss phase (any secondary phases) (conductivities). Expanding simpler LSTZ,27Chen designed our “x series” general formula [Li(2/3)xSr1-x(VA″)(1/3)x][(5B)(4/3)x(4B)1-(4/3)x]O3-δ. Here, site occupied Li+, Sr2+, vacancies VA″ (in Kröger–Vink notation), B (presumably random) mixture 5B (5+ B-site) cations, equal moles Ta5+ Nb5+ 4B (4+ Zr4+ Sn4+ (or Hf4+) cations LSTNZH). Omitting brevity, formulas (Li2/3xSr1-x)(Ta2/3xNb2/3xZr0.5(1-4/3x)Sn0.5(1-4/3x)O3-δ x (Li2/3xSr1-x)(Ta2/3xNb2/3xZr0.5(1-4/3x)Hf0.5(1-4/3x)O3-δ LSTNZH. investigated (primary secondary) formation XRD. Figures 2C 2D present XRD patterns LSTNZH, respectively. = 8/16, group Pm 3¯ m, matches KTaO3 (PDF #38–1,470) value increases 9/16 higher. At ≥ 9/16, LiNbO3-prototyped rhombohedral (space R3c) Sr2.83Ta5O15-prototyped tetragonal P4/mbm) formed, consequently triggered precipitation SnO2 ZrO2 phases. corresponding separation evident (SEM) energy-dispersive spectroscopy (EDS) maps S2. single-phase up trace found. > primary becomes instead phase. Based results, conclude mainly determined value, threshold (for appearance large depends difference radii. (x 9/16) series, attributed larger radii between (∼4.17%) Hf4+ (1.39%), calculated Shannon (Table S4).43Shannon R.D. Revised effective systematic interatomic distances halides chalcogenides.Acta Crystallogr. 1976; 32: 751-767https://doi.org/10.1107/S0567739476001551Crossref (54851) radius makes more difficult form solution test hypothesis, benchmarked Nb co-doped counterparts S3, again implies poor site. formability system, adopted “natural selection” composition optimization strategy described (Figures S4–S6; Tables S5 S6; Note S2) synthesize guided SEM-EDS quantification region iterative procedure. Accordingly, “y optimal ratio (Li2/3ySr1-y)(Ta0.334Nb0.347Zr0.211Sn0.108)O3-δ developed. y 2E) exhibit series. (y 0.6), main Li(Ta, Nb)O3. workflows illustrated S7. characterizations, focus obtained quantify fractions, performed Rietveld refinements S8) S9). Table fractions S10) 3A 3B S11 compares methods, consistent. exception 10/16), refinement accuracy low multiple peak overlaps likely accurate. measured as-synthesized specimens. 3C illustrates variable (that correlates Li+ concentration, 23y, 13y, site) (fitted impedance spectra S1) When 0.387, σbulkLSTNZS 0.004 (the lowest). As 0.5, orders 0.118 mS/cm. maximized even fractions. Hence, change dominant carrier vacancy (rather purities) ≤ region. contrast, when 9/16. Although nominal highest 0.6 3C, existence Sr2.83Ta5O15, LiTaO3, LiNbO3 indicates actual less amount. Therefore, reduces 0.14 0.6. maximum 0.218 8/16; 0.11 mS/cm). Given samples similar (LSTNZS, 8/16), justify selection stoichiometry gives “w fabricated (Li0.375Sr0.4375)(Ta0.334Nb0.347Zr0.319-wSnw)O3-δ, w dictates fraction S12A S12C indicate increasing Sn/Zr fra