The recent discovery of superconductivity in thin films of doped NdNiO2 confirmed that Ni1+/Ni2+ nickelates can exhibit physics similar to the superconducting cuprates. All known Ni1+/Ni2+ nickelates with infinite NiO2 layers belongs to the T'-type Ln(n+1)Ni(n)O(2n+2) (n = 2, 3, infinity) homologous series. We expanded the chemistry of the T'-type nickelates by preparing two new oxyfluorides La4Ni3O8F1 and La4Ni3O8F2. Due to the high thermodynamic stability of LaOF admixture, these compounds are metastable and can be prepared only by the low-temperature fluorination of the appropriate T'-type nickelate. A novel facile solvothermal fluorination method was developed for metastable oxyfluorides preparation by filling anion vacancies in parent structures. The high solubility of XeF2 in acetonitrile and polarity of the solvent allowed for lower reaction temperature. The validity of the method was demonstrated by the preparation of a known oxyfluoride, SrCoO2.5F0.5, at unprecedented low temperature (100°C). Additionally, two new oxyfluorides with the idealized stoichiometry of La4Ni3O8F1 and La4Ni3O8F2. were prepared by the solvothermal fluorination via the La4Ni3O8 infinite-layer intermediate. Rietveld structure refinement and electron diffraction data for oxyfluorides will be presented. The proposed method allows the preparation of metastable oxyfluorides, utilizes only inexpensive commercial autoclaves, and can potentially find widespread utilization in materials synthesis.

Low-temperature solvothermal fluorination method and synthesis of La4Ni3O8Fx oxyfluorides via the La4Ni3O8 infinite-layer intermediate

ACS Spring Meeting 2021

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