Crystal Chemistry of a Nickelate Superconductor: La/Pr Distribution, Oxygen Stoichiometry, and High-Pressure Structural Evolution in La2PrNi2O7.
5 affiliations
- 1Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC) , c/Sor Juana Inés de la Cruz 3, Cantoblanco, Madrid28049, Spain.
- 2European Synchrotron Radiation Facility (ESRF), 71 Avenue des Martyrs, CS40220, Grenoble38043, France.
- 3Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing100190, China.
- 4Max Planck Institute for Chemical Physics of Solids, Dresden01187, Germany.
- 5Institut Laue-Langevin (ILL) , 71 Avenue des Martyrs, BP 156, Grenoble Cedex 938042, France.
Abstract
We report a comprehensive structural characterization of La2PrNi2O7, a bilayer Ruddlesden-Popper nickelate that has been described to exhibit high-temperature superconductivity under hydrostatic pressure. Synchrotron X-ray diffraction (SXRD) data and high-resolution neutron powder diffraction (NPD) data, collected at ambient pressure, together with NPD data recorded under pressures up to 8.42 GPa in a Paris-Edinburgh cell, have been analyzed by the Rietveld method in the orthorhombic Amam space group (No. 63). This work aims at providing precise bulk structural benchmarks─site-selective cation distribution, oxygen stoichiometry, and the pressure evolution of the Ni-O-Ni bond geometry─that are essential inputs for theoretical models. High-resolution NPD, which offers a strong La/Pr scattering-length contrast, yields refined La/Pr occupancies that suggest a slight preference of Pr for the outer rock-salt site (La2/Pr2), although the deviation from a random distribution does not exceed three standard deviations and is therefore not statistically conclusive. NPD also assesses the full oxygen stoichiometry of the specimen under study. Under applied pressure up to 8.42 GPa (below the superconducting critical pressure Pc ≈ 11 GPa), the orthorhombic structure is retained with a systematic compression of all lattice parameters, a reduction of the unit-cell volume of ∼4.9%, and a progressive straightening of the out-of-plane Ni-O-Ni bond angle. No structural phase transition to the tetragonal I4/mmm symmetry is observed in the pressure range studied, consistent with the superconducting onset occurring above Pc ≈ 11 GPa. Cooling to 5 K at 8.42 GPa produces no measurable additional structural change, indicating that precursor distortions to the superconducting state are subtle.
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BibTeX
@article{gainza2026crystal,
title = {{Crystal Chemistry of a Nickelate Superconductor: La/Pr Distribution, Oxygen Stoichiometry, and High-Pressure Structural Evolution in La2PrNi2O7.}},
author = {Javier Gainza and Lifen Shi and Gang Wang and Ningning Wang and María Teresa Fernández-Díaz and Stanislav Savvin and Jinguang Cheng and José Antonio Alonso},
journal = {Inorganic chemistry},
year = {2026},
month = oct,
doi = {10.1021/acs.inorgchem.6c03000},
url = {https://europepmc.org/article/MED/42895421},
note = {CC BY},
}
RIS
TY - JOUR
TI - Crystal Chemistry of a Nickelate Superconductor: La/Pr Distribution, Oxygen Stoichiometry, and High-Pressure Structural Evolution in La2PrNi2O7.
AU - Javier Gainza
AU - Lifen Shi
AU - Gang Wang
AU - Ningning Wang
AU - María Teresa Fernández-Díaz
AU - Stanislav Savvin
AU - Jinguang Cheng
AU - José Antonio Alonso
PY - 2026
DA - 2026/10/01
JO - Inorganic chemistry
DO - 10.1021/acs.inorgchem.6c03000
UR - https://europepmc.org/article/MED/42895421
AB - We report a comprehensive structural characterization of La2PrNi2O7, a bilayer Ruddlesden-Popper nickelate that has been described to exhibit high-temperature superconductivity under hydrostatic pressure. Synchrotron X-ray diffraction (SXRD) data and high-resolution neutron powder diffraction (NPD) data, collected at ambient pressure, together with NPD data recorded under pressures up to 8.42 GPa in a Paris-Edinburgh cell, have been analyzed by the Rietveld method in the orthorhombic Amam space group (No. 63). This work aims at providing precise bulk structural benchmarks─site-selective cation distribution, oxygen stoichiometry, and the pressure evolution of the Ni-O-Ni bond geometry─that are essential inputs for theoretical models. High-resolution NPD, which offers a strong La/Pr scattering-length contrast, yields refined La/Pr occupancies that suggest a slight preference of Pr for the outer rock-salt site (La2/Pr2), although the deviation from a random distribution does not exceed three standard deviations and is therefore not statistically conclusive. NPD also assesses the full oxygen stoichiometry of the specimen under study. Under applied pressure up to 8.42 GPa (below the superconducting critical pressure Pc ≈ 11 GPa), the orthorhombic structure is retained with a systematic compression of all lattice parameters, a reduction of the unit-cell volume of ∼4.9%, and a progressive straightening of the out-of-plane Ni-O-Ni bond angle. No structural phase transition to the tetragonal I4/mmm symmetry is observed in the pressure range studied, consistent with the superconducting onset occurring above Pc ≈ 11 GPa. Cooling to 5 K at 8.42 GPa produces no measurable additional structural change, indicating that precursor distortions to the superconducting state are subtle.
SN - 0020-1669
SN - 1520-510X
ER -