Point Defect Modeling of La2CuO4-Based Superconductors

doi:10.1111/j.1151-2916.1994.tb06960.x

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Wiley InterScience

Journal of the American Ceramic Society

Volume 77 Issue 1, Pages 81 - 88

Published Online: 8 Mar 2005

Published on behalf of the American Ceramic Society (ACerS)

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Point Defect Modeling of La₂CuO₄-Based Superconductors

Li Shen, ^* ¹ Paul A. Salvador ¹ Thomas O. Mason ^* ¹

¹ Department of Materials Science and Engineering and Science and Technology Center for Superconductivity, Northwestern University, Evanston, Illinois 60208

^* Member, American Ceramic Society.

J. W. Halloran—contributing editor

Supported by the U.S. Department of Energy under Grant No. FG02-84ER45097 (LS, TOM) and the National Science Foundation, Office of Science and Technology Centers, under Grant No. DMR-91-20000 (PAS, TOM).

ABSTRACT

A point defect modeling study of the oxygen nonstoichiometry and high-temperature electrical properties of La_2−xAE_xCuO_4−y (AE = Ba, Sr, and Ca) systems indicates that, whereas oxygen excess (y < 0) due to oxygen interstitials predominates as x→ 0, oxygen deficit (y > 0) results primarily from dopant-vacancy associates at large x; isolated oxygen vacancies are apparently minority defect species. The onset of oxygen deficiency due to dopant-vacancy associates occurs at x∼ 0.15 in the AE = Ba and Sr systems but at x∼ 0.05 in the AE = Ca system. Ideal ionic point defect behavior persists to x∼ 0.4 in the AE = Ba and Ca systems and to x∼ 0.5 in the AE = Sr system. A premature flattening of the electrical properties above x∼ 0.2 occurs in the AE = Ba and Sr systems. Reasons for the extensive range of ideal ionic behavior and for the onset of degenerate electronic behavior are discussed, as are ramifications for high-T_c superconductivity in these materials.