High-pressure crystal growth and investigation of the metal-to-metal transition of Ruddlesden–Popper trilayer nickelates La₄Ni₃O₁₀

摘要

Single crystals of Ruddlesden–Popper nickelates La₄Ni₃O₁₀ were grown by means of the floating-zone technique at oxygen pressure of 20 bar. Our results reveal the effects of the annealing process under pressure on the crystal structure. We present the requirements for crystal growth and show how a reported ferromagnetic impurity phase can be avoided. The different growth and post-annealing processes result in two distinct phases 𝑃 21∕𝑎 and Bmab in which the metal-to-metal transitions occur at 152 K and 136 K, respectively.

材料

• La₄Ni₃O₁₀

方法

• floating-zone technique
• high-pressure annealing
• crystal structure determination

关键词

• metal to metal transition
• ferromagnetic impurity phase
• p21/a phase
• bmab phase

亮点

• High oxygen pressure (20 bar) floating zone growth of La₄Ni₃O₁₀ single crystals.
• Demonstrates how to avoid a reported ferromagnetic impurity phase.
• Reveals two distinct phases with different metal-to-metal transition temperatures.

结论

• Two distinct phases P₂₁/a and Bmab are obtained.
• Metal-to-metal transitions occur at 152 K for P₂₁/a and 136 K for Bmab.
• The ferromagnetic impurity phase can be avoided by proper growth and post-annealing processes.

主要论断

• Two crystallographic modifications of La₄Ni₃O₁₀ single crystals are obtained: orthorhombic Bmab (T_MM = 152 K) and monoclinic P₂₁/a (T_MM = 136 K).
  • 证据: XRD Rietveld refinement identifies phases,Magnetic susceptibility and specific heat show sharp anomalies at these temperatures
• The P₂₁/a phase is the thermodynamically stable phase at room temperature, as established by annealing experiments.
  • 证据: Biphasic samples show conversion from Bmab to P₂₁/a upon annealing at 1000°C in flowing oxygen,Mass fraction of P₂₁/a increases after annealing

研究流程

• single_crystal_growth — Two types of crystals: S₁ (Bmab) and S₂ (P₂₁/a).
  • 材料: La₄Ni₃O₁₀ polycrystalline rods
  • 方法: High-pressure optical floating zone (HKZ, SciDre); Oxygen pressure 20 bar; Xe arc lamp
  • 观察: Shiny boules obtained; S₁ (as-grown), S₂ (annealed at 950°C, 20 bar O₂, 2 h)
• structural_and_physical_characterization — Clear metal-to-metal transitions at distinct temperatures for the two phases.
  • 材料: S₁ and S₂ single crystals
  • 方法: Powder XRD (Rietveld refinement); Laue backscattering; Magnetic susceptibility (SQUID); Specific heat (PPMS)
  • 观察: Laue spots confirm single crystallinity; S₁: Bmab phase, MMT at 152 K; S₂: P₂₁/a phase, MMT at 136K; No FC/ZFC hysteresis, no ferromagnetic impurity; Entropy change ΔS_MM ≈ 1.4–1.6 J/(mol K)