Suppression of superconductivity in La1.85Sr0.15Cu1-yNiyO4: The relevance of local lattice distortions

Abstract

The effect of Ni substitution upon the local structure of La{sub 1.85}Sr{sub 0.15}Cu{sub 1-y}Ni{sub y}O{sub 4} is commonly neglected when addressing the Ni-induced destruction of the superconducting state at y{approx_equal}0.03 and a metal-insulator transition at y{approx_equal}0.05. It is also sometimes assumed that direct substitution of a dopant into the CuO{sub 2} planes has a detrimental effect on superconductivity due to in-plane lattice distortions around the dopants. We present here results from angular-dependent x-ray absorption fine structure (XAFS) measurements at the Ni, La and Sr K-edges of oriented powders of La{sub 1.85}Sr{sub 0.15}Cu{sub 1-y}Ni{sub y}O{sub 4} with y=0.01, 0.03, 0.06. A special magnetic alignment geometry allowed us to measure pure c and (subform(ab)) oriented XAFS at the Ni K-edge in identical fluorescence geometries. Both the near-edge absorption spectra (XANES) and the XAFS unequivocally show that the NiO{sub 6} octahedra are largely contracted along the c-axis, by {approx_equal} 0.16 Aa. Surprisingly, the Ni-O planar bonds and the Ni-O-Cu/Ni planar buckling angle are nearly identical to their Cu counterparts. The NiO{sub 6} octahedral contraction drives the macroscopic c-axis contraction observed with Ni-doping. The local c-axis strongly fluctuates, due to the different NiO{sub 6} and CuO{sub 6} octahedral configurations and the much stronger bonding of a La{sup +3} ion than a Sr{sup +2} ion to the O(2) apical oxygens. We discuss the relevance of these findings to the mechanisms of T{sub c} suppresion and hole-localization by Ni dopants.

Department(s)

Materials Science and Engineering

International Standard Serial Number (ISSN)

1551-7616, 0094-243X

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2026 AIP Publishing LLC, All rights reserved

Publication Date

2001-02-26

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