RT Journal Article
T1 Stabilization of Infinite-Layer NdNi<sub>1–<i>x</i></sub>Al<sub><i>x</i></sub>O<sub>2</sub> nickelates containing monovalent Ni as bulk polycrystalline materials
A1 Gainza, Javier
A1 López, Carlos A.
A1 Silva, Romualdo S.
A1 Serrano Sánchez, Federico
A1 Rodrigues, João Elias F. S.
A1 Skorynina, Alina
A1 Rosa, Angelika D.
A1 Nemes, Norbert Marcel
A1 Biskup Zaja, Nevenko
A1 Fernández Díaz, María T.
A1 Martínez, José Luis
A1 Alonso, José Antonio
AB The series of RNiO2 (where R is a rare-earth element) oxides with infinite-layer structure constitutes a novel family of high-temperature superconductors, with the same structural framework as the well-known high-Tc cuprates but with Ni instead of Cu for the covalent matrix. Despite these similarities, superconductivity has only been described in nickelates in thin films, but its origin remains controversial, being associated either with a reduction of Ni or with the stress effect in the monolayer. In the present work, we have successfully synthesized infinite-layer bulk samples with nominal formulas NdNiO2 and NdNi0.9Al0.1O2+δ, by topotactic reduction from the corresponding “oxidized” perovskites with NdNi1–xAlxO3 (x = 0, 0.1) stoichiometry. We show that the substitution of 10% Al at the octahedral Ni positions contributes to the stabilization of the infinite-layer structure. Indeed, the topotactic removal of axial oxygen atoms on the [NiO6] octahedra leads to a chemical reduction of Ni3+ to Ni+ and thus, in the absence of unreducible Al atoms, to structural instabilities. Synchrotron X-ray diffraction (SXRD) data, collected after treatment at increasing temperatures and therefore increasingly reducing conditions, permitted us to unveil the structural evolution upon oxygen removal. Additional neutron diffraction measurements allowed the axial oxygen content to be assessed and revealed an almost monovalent oxidation state for Ni in the Al-containing sample. In addition, the neutron data evidenced the absence of occluded, long-range ordered hydrogen in the crystal structure, consistent with observations on LaNiO2 materials. Spectroscopic results from X-ray absorption spectroscopy (XAS) show that Ni ions are indeed reduced to the Ni+ oxidation state, in agreement with the crystallochemical data of NdNiO2. The local atomic structure around the Ni absorber was evaluated using the EXAFS technique and showed that Al doping enhances the rigidity of the Ni–O bonds and medium-range interactions within the Ni–Nd sublattice. Magnetic measurements could not provide evidence of superconductivity, as susceptibility is masked by the presence of tiny amounts of Ni metal.
PB American Chemical Society
SN 0897-4756
YR 2025
FD 2025-06-25
LK https://hdl.handle.net/20.500.14352/125217
UL https://hdl.handle.net/20.500.14352/125217
LA eng
NO Gainza, J.; López, C. A.; Silva, R. S.; Serrano-Sánchez, F.; Rodrigues, J. E. F. S.; Skorynina, A.; Rosa, A. D.; Nemes, N. M.; Biškup, N.; Fernández-Díaz, M. T.; Martínez, J. L.; Alonso, J. A. Stabilization of Infinite-Layer NdNi 1– x Al x O2 Nickelates Containing Monovalent Ni as Bulk Polycrystalline Materials. Chem. Mater. 2025, 37 (13), 4729–4742. https://doi.org/10.1021/acs.chemmater.5c00507.
NO © 2025 The AuthorsHC-5817.
NO Ministerio de Ciencia e Innovación (España)
NO Agencia Estatal de Investigación (España)
NO European Commission
NO European Synchrotron Radiation Facility
DS Docta Complutense
RD 18 dic 2025