We have investigated the influence of Ca ion substitution on the structural and superconducting properties of (Nd1−xCax)(Ba1.6La0.4)Cu3Oz system. Magnetization, x-ray diffraction, and neutron diffraction studies have been carried out on a series of compounds with x=0.0-0.6. The superconducting transition temperature Tc, determined from magnetization measurements, increases with increasing Ca2+ substitution. Neutron diffraction studies reveal that these compounds crystallize in a tetragonal structure (space group P4/mmm). A detailed analysis of the neutron diffraction data reveals that Ca and La ions are intermixed at the nominal Ba and Nd sites. While a major fraction of Ca ions occupy the usual Nd site, a small fraction occupies the Ba site. Consequently, the corresponding amount of La substitutes at the nominal Nd site. The intermixing of Ca and La sites randomizes the chain site oxygens leading to a tetragonal structure despite an oxygen content close to 7.0 for all the Ca doped samples. Further increase in Ca content leads to change in its coordination from sixfold to eightfold at x>=0.4.
A. G. Joshi et al., "Neutron Structural Studies on the Superconducting (Nd1-xCax)(Ba₁.₆La₀.₄)Cu₃Oz System," Journal of Applied Physics, American Institute of Physics (AIP), Apr 2009.
The definitive version is available at http://dx.doi.org/10.1063/1.3116532
Keywords and Phrases
Calcium Compounds; Crystal Structure; Magnetisation; Neodymium Compounds; Superconducting Transition Temperature; X-Ray Diffraction; Barium compounds; High-temperature superconductors; Lanthanum compounds; Neutrons - Diffraction; Space groups
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