Source zotero
Authors Keke Jiao, Yongjian Wang, Rui Niu, Wanli Zhu, Huixin Xu, Li Zheng, Changjin Zhang
arXiv / Publisher https://pubs.aip.org/aip/jap/article/139/3/033901/3377469/Insulator-to-metal-transition-in-Co-doped-La3Ni2O7
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Published 2026-01-20
Research paradigm Experimental
Sample form Unknown

Summary

The effects of Co doping in a series of La3Ni2−xCoxO7−δ samples before and after high oxygen pressure annealing have been investigated. The structural refinemen

Materials

Methods

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Keywords

Highlights

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Conclusions

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Main claims

  • High oxygen pressure annealing induces an insulator-to-metal transition in Co-doped La3Ni2O7−δ, leading to metallic conductivity above 20 K.
    • Evidence: The annealed La3Ni2−xCoxO7−δ samples exhibit an insulator-to-metal transition, and the metallic-like conductivity could be achieved above ≈20 K in Co-doped samples
  • The increase in oxygen content during annealing raises the average Ni valence state, which is responsible for the enhanced electrical conductivity.
    • Evidence: The annealing treatment results in an increase in the oxygen content and the average valence state of Ni ions of the La3Ni2−xCoxO7−δ samples,The approach of the average valence state of Ni to 2.5 is believed to be favorable for the occurrence of superconductivity

Workflow

  • sample preparation — Co-doped La3Ni2O7−δ samples with high doping level (x up to 0.3) were successfully synthesized via sol-gel.
    • Materials: Ni(NO3)2·6H2O; La2O3; Co(NO3)2·6H2O; citric acid; nitric acid
    • Methods: sol-gel method; stepwise heating (160°C, 400°C, 800°C); pelleting; sintering at 1100°C in air for 24 h
    • Observations: blackish-gray powders after organic removal; single-phase orthorhombic (Amam) for all doping
  • high oxygen pressure annealing — High oxygen pressure annealing effectively increases oxygen content and reduces structural distortion.
    • Materials: as-prepared La3Ni2−xCoxO7−δ pellets
    • Methods: high-temperature high-pressure tube furnace (OTF-1200X-HP-30)
    • Observations: mass increase ≈1.13% on average indicating oxygen uptake; lattice parameters decrease (a and c) and Ni-O-Ni bond angles increase
  • structural and electronic characterization — Insulator-to-metal transition is achieved in Co-doped samples after high oxygen pressure annealing, with metallic conduction above ≈20 K.
    • Materials: powder samples before and after annealing
    • Methods: X-ray diffraction (XRD) with Rietveld refinement (GSAS); X-ray photoelectron spectroscopy (XPS); four-probe resistivity; SQUID magnetometry
    • Observations: unit cell volume increases with Co doping; Ni valence increases from ≈2.43 to ≈2.48 after annealing; magnetic susceptibility largely unchanged by annealing; resistivity shows insulator-to-metal transition after annealing: metallic behavior above 20K