Extensive x-ray and neutron scattering experiments and additional transmission electron microscopy results reveal the partial decomposition of Nd2-xCexCuO4±δ (NCCO) in a low-oxygen-fugacity environment such as that typically realized during the annealing process required to create a superconducting state. Unlike a typical situation in which a disordered secondary phase results in diffuse powder scattering, a serendipitous match between the in-plane lattice constant of NCCO and the lattice constant of one of the decomposition products, (Nd, Ce) 2O3, causes the secondary phase to form an oriented, quasi-two-dimensional epitaxial structure, Consequently, diffraction peaks from the secondary phase appear at rational positions (H, K, 0) in the reciprocal space of NCCO. Additionally, because of neodymium paramagnetism, the application of a magnetic field increases the low-temperature intensity observed at these positions via neutron scattering. Such effects may mimic the formation of a structural superlattice or the strengthening of antiferromagnetic order of NCCO, but the intrinsic mechanism may be identified through careful and systematic experimentation. For typical reduction conditions, the (Nd, Ce) 2O3 volume fraction is approximately 1%, and the secondary-phase layers exhibit long-range order parallel to the NCCO CuO 2 sheets and have a typical thickness of approximately 100 Å. The presence of the secondary phase should also be taken into account in the analysis of other experiments on NCCO, such as transport measurements.
|Original language||English (US)|
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|State||Published - Sep 2004|
Bibliographical noteFunding Information:
The authors would like to thank N. Kaneko for his efforts in constructing the reduction furnace and maintaining the crystal growth facility at Stanford University, and A. Arvanitaki for assistance in orienting the TEM sample. The authors are also grateful for valuable comments by J.M. Tranquada, N.P. Armitage, H. Eisaki, E.M. Motoyama, T.W. Klimczuk, and D. Petitgrand. The authors would like to thank J.W. Lynn for technical assistance with the neutron scattering measurements at NIST. Finally, the authors wish to acknowledge P. Dai, H.J. Kang, J.W. Lynn, M. Matsuura, and S.C. Zhang for discussing their data with us. SSRL is supported by the DOE Office of Basic Energy Sciences, Division of Chemical Sciences and Materials Sciences. The work at Stanford University was furthermore supported by the U.S. Department of Energy under Contracts No. DE-FG03-99ER45773 and No. DE-AC03-76SF00515, and by NSF CAREER Award No. DMR9985067.