Structural features and electronic properties of La₄Ni₃O₁₀ with oxygen vacancies

摘要

Ruddlesden-Popper (RP) nickelates are a promising class of high-temperature superconductors, with superconducting transition temperatures exceeding the boiling point of liquid nitrogen. However, oxygen nonstoichiometry remains a persistent challenge that commonly presents in all RP nickelates. Understanding the formation of oxygen vacancies, their ordering patterns, and their impact on superconductivity is crucial, especially in the newly discovered L⁢a4⁢N⁢i3⁢O₁₀. In this study, the first-principles structural calculations reveal the formation of in-plane oxygen vacancy chains in L⁢a4⁢N⁢i3⁢O₁₀, a key structural feature observed under both ambient and pressurized conditions. These vacancies induce significant lattice distortion and generate residual electrons that hybridize with the Ni 𝑑𝑧2 orbital, altering the sign of the hopping integral between the 𝑑𝑧2 orbitals. Furthermore, the vacancies alter the N⁢i2+/N⁢i3+ ratio, lower the 𝑑𝑧2 orbital energy, and decrease the 𝑑𝑧2 orbital density of states at the Fermi level. Interestingly, at higher vacancy concentrations, the vacancy chains tend to align diagonally along the out-of-plane direction. The phase diagram of L⁢a4⁢N⁢i3⁢O₁₀ exhibits a narrow stability range at ambient pressure, which expands under applied pressure, aligning with the high-oxygen-pressure conditions required for its synthesis. Importantly, these vacancy chains broaden the optical conductivity peak, which could serve as a marker for their detection. Our findings offer valuable insights into the distribution of oxygen vacancies, their role in modifying the electronic structure, and their influence on optical conductivity in L⁢a4⁢N⁢i3⁢O₁₀.

材料

• La₄Ni₃O₁₀ with oxygen vacancies

方法

• first-principles structural calculations

关键词

• oxygen vacancies
• vacancy chains
• lattice distortion
• hybridization
• ni dz2 orbital
• optical conductivity

亮点

• The phase diagram of La₄Ni₃O₁₀ exhibits a narrow stability range at ambient pressure, which expands under applied pressure.
• Vacancy chains broaden the optical conductivity peak, which could serve as a marker for their detection.

结论

• Oxygen vacancy chains induce significant lattice distortion and generate residual electrons that hybridize with the Ni dz2 orbital.
• Vacancies lower the dz2 orbital energy and decrease the dz2 orbital density of states at the Fermi level.
• At higher vacancy concentrations, the vacancy chains tend to align diagonally along the out-of-plane direction.

主要论断

• Oxygen vacancies in La₄Ni₃O₁₀ form energetically favorable in-plane chain structures at both ambient and high pressure.
  • 证据: DFT total energy comparisons show chain arrangements have lowest energy.
• These vacancy chains induce significant lattice distortion, alter the Ni₂+/Ni₃+ ratio, lower dz2 orbital energy, and decrease dz2 DOS at Fermi level.
  • 证据: Band structure shows defect states and downward shift of dz2; Wannier analysis shows altered hopping integrals.
• The formation energy of oxygen vacancies in La₄Ni₃O₁₀ is significantly higher than in La₃Ni₂O₇, explaining the lower vacancy concentration observed experimentally.
  • 证据: Phase diagram calculations show higher Ef (3.72-6.20 eV) compared to La₃Ni₂O₇.

研究流程

• DFT Structural Relaxation — Oxygen vacancies in La₄Ni₃O₁₀ preferentially form in-plane chain configurations.
  • 材料: La₄Ni₃O₁₀-δ
  • 方法: DFT (VASP) with PBE+U (U=3 eV)
  • 观察: Inner apical oxygen vacancies are most stable; vacancies form in-plane chains
• Band Structure and Wannier Analysis — Oxygen vacancies lower dz2 orbital energy and reverse sign of hopping integral between dz2 orbitals.
  • 材料: La₄Ni₃O₁₀-δ
  • 方法: DFT band structure; Wannier function downfolding (Wannier90)
  • 观察: Defect state from Ni VO dz2 at ~-0.7 eV; downward shift of Ni per dz2; altered hopping integrals
• Optical Conductivity Calculation — Broadening of optical conductivity peak serves as characteristic signature of vacancy chain formation.
  • 材料: La₄Ni₃O₁₀-δ
  • 方法: DFT optical conductivity (intraband and interband)
  • 观察: Peak at 1.78 eV broadens with vacancy chains; new low-energy peak appears at higher concentrations
• Phase Diagram Construction — Pressure enhances stabilization of La₄Ni₃O₁₀, consistent with high-oxygen-pressure synthesis.
  • 材料: La₄Ni₃O₁₀
  • 方法: Chemical potential diagram (Chesta code)
  • 观察: Narrow stability range at 0 GPa; expands at 30 GPa; high formation energy for vacancies