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

Session: Solid-State Inorganic Chemistry:  

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, SrCoO_2.5F_0.5, 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.