Low-temperature solvothermal fluorination method and synthesis of La4Ni3O8F oxyfluorides via the La4Ni3O8 infinite-layer intermediate

Pure Fluorine Intercalation into Brownmillerite Oxide Thin Films by Using Ionic Liquid Gating

“…While SrCoO 2.5 is an antiferromagnetic (AFM) insulator with a Neél temperature of T N = 537 K, 34 the temperature-dependent magnetization of almost strain-free SrCoO 2.5 F 0.5 /LSAT (Figure 5a) exhibited a ferromagnetic (FM) phase transition with the Curie temperature T C of ∼110 K. The field-dependent magnetization showed a small hysteresis loop at 2 K, indicating its characteristics as a soft ferromagnet (Figure 5b) with the saturation magnetizations M S of 1.9 μ B /Co. These behaviors are in contrast to SrCoO 2.5 F x powder obtained via fluorination reactions, which exhibits a canted AFM, 16,17 with a smaller magnetic moment M S of ∼1 μ B /Co, 17 possibly due to oxygen loss and/or incomplete fluorine filling. The obtained value of M S in our SrCoO 2.5 F 0.5 film aligns well with La 0.5 Sr 0.5 CoO 3 perovskite (1.85 μ B /Co for the film 35 and 1.92 μ B /Co for the bulk 45 ) with the Co 3.5+ state achieved through cation substitution.…”

“…The lattice constants of the obtained films are comparable to or slightly larger than those of F-intercalated SrCoO 2.5 powder, with a = 3.8574(3) 16 and 3.8549(1). 17 The presence and distribution of F anions in the films after ILG treatment was investigated using multiple probes, including X-ray absorption spectroscopy (XAS), scanning electron microscopy energy-dispersive X-ray (SEM-EDX), and X-ray photoelectron spectroscopy (XPS) depth profile. As shown in Figure 3a, the F K-edge XAS spectra exhibit sharp and broad peaks at about 688 eV (peak A) and 692 eV (peak B), respectively, as in the case of the SrFeO 3−x F y thin film.…”

“…Similar to La 0.5 Sr 0.5 CoO 3 with a formal valence Co 3.5+ , 31−35 this SrCoO 2.5 F 0.5 film has a ferromagnetic metallic state, previously unreported in the Sr−Co−O−F systems. 16,17,19 Our approach uniquely allows fluoride anion insertion without altering the oxygen composition until the anion vacancies are fully filled, which is advantageous over conventional fluorination methods. We also successfully applied this method to SrFeO 2.5 thin films, leading to the formation of SrFeO 2.5 F 0.5 , demonstrating its potential applicability to a wider range of transition-metal oxides with anion vacancies.…”

“…The F 2 gas treatments of both SrFeO 2 and SrFeO 2.5 result in the formation of SrFeO 2 F, − likely due to the stability of Fe 3+ . For cobalt, while SrCoO 2.5 F 0.5 is reported to be obtained from SrCoO 2.5 , using F 2 gas or XeF 2 , the detailed anion composition remains underexamined. , Although fluoropolymers such as polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE) are safer alternatives to corrosive F 2 gas, ,− they often lead to reduced products (e.g., SrCoO 2.5 → SrCoO 1.9(4) F 0.5(1) ) . A significant issue with the reaction using fluoropolymers is that their carbon content extracts oxygens from precursors, leading to oxygen deficiencies …”

Development of Electrochemical Anion Doping Technique for Expansion of Functional Material Exploration

“…[33,34] Solvothermal reaction also use high pressure environment in an autoclave with solvent. [35,36] In mechano-chemical synthesis, starting materials are reacted by applying high mechanical energy. [37,38] These novel techniques expand the horizon of mixed-anion functional materials, however, the degree of anion doping is controlled in an indirect manner by tuning the amount of anion sources, reaction time, temperature, and total pressure.…”