TY - JOUR
T1 - Ni-induced local distortions in La1.85Sr0.15Cu1-yNiyO4 and their relevance to Tc suppression
T2 - An angular-resolved XAFS study
AU - Haskel, Daniel
AU - Stern, Edward A.
AU - Polinger, Victor
AU - Dogan, Fatih
PY - 2001/9/1
Y1 - 2001/9/1
N2 - We present results from angular-resolved x-ray-absorption fine-structure (XAFS) measurements at the Ni, La, and Sr K edges of oriented powders of La1.85Sr0.15Cu1-yNiyO 4, with y=0.01, 0.03, 0.06. A special magnetic alignment procedure allowed us to measure pure ĉ- and ab-oriented XAFS at the Ni K edge in identical fluorescence geometries. Both the x-ray-absorption near-edge structure and the XAFS unequivocally show that the NiO6 octahedra are contracted along the c axis by ≈0.32 Å relative to CuO6 octahedra while the in-plane distances of NiO6 and CuO6 octahedra are the same within 0.01 Å. The NiO6 octahedral contraction drives the average ĉ axis contraction measured by diffraction with increasing content of Ni. The local ĉ axis shows strong spatial fluctuations, due to the different NiO6 and CuO6 octahedral configurations and the stronger bonding of a La3+ ion than a Sr2+ ion to the O(2) apical oxygens of such octahedra. We discuss the relevance of these findings to the mechanisms of loss of superconductivity at y≈0.03 and hole localization above y≈0.05 by Ni dopants.
AB - We present results from angular-resolved x-ray-absorption fine-structure (XAFS) measurements at the Ni, La, and Sr K edges of oriented powders of La1.85Sr0.15Cu1-yNiyO 4, with y=0.01, 0.03, 0.06. A special magnetic alignment procedure allowed us to measure pure ĉ- and ab-oriented XAFS at the Ni K edge in identical fluorescence geometries. Both the x-ray-absorption near-edge structure and the XAFS unequivocally show that the NiO6 octahedra are contracted along the c axis by ≈0.32 Å relative to CuO6 octahedra while the in-plane distances of NiO6 and CuO6 octahedra are the same within 0.01 Å. The NiO6 octahedral contraction drives the average ĉ axis contraction measured by diffraction with increasing content of Ni. The local ĉ axis shows strong spatial fluctuations, due to the different NiO6 and CuO6 octahedral configurations and the stronger bonding of a La3+ ion than a Sr2+ ion to the O(2) apical oxygens of such octahedra. We discuss the relevance of these findings to the mechanisms of loss of superconductivity at y≈0.03 and hole localization above y≈0.05 by Ni dopants.
UR - http://www.scopus.com/inward/record.url?scp=0035445982&partnerID=8YFLogxK
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AN - SCOPUS:0035445982
SN - 0163-1829
VL - 64
SP - 1045101
EP - 10451010
JO - Physical Review B - Condensed Matter and Materials Physics
JF - Physical Review B - Condensed Matter and Materials Physics
IS - 10
M1 - 104510
ER -