The role of selected f ions in the suppression of high-Tc superconductivity.
The initial observations of superconductivity at temperatures above 77 K in copper-oxide based materials was surprising from a variety of different perspectives. Among the unexpected findings were reports of superconductivity for the series RBa{sub 2}Cu{sub 3}O{sub 7} where R is a rare earth (Y, Nd-Tm), which may carry a large, local magnetic moment. Superconductivity was subsequently demonstrated for all 4f analogs in this series except Ce, Pr, and Tb. In addition to the RBa{sub 2}Cu{sub 3}O{sub 7} series, there are several other CuO based series of superconductors that are formed by substituting R ions. The most studied of these are listed in Table 1, together with the f ions that form isostructural compounds and their superconducting critical temperatures (T{sub c}). The presence of an R ion with a large magnetic moment does not significantly influence the superconductivity. In contrast, even the presence of small concentrations of magnetic impurity ions in a conventional superconductor inhibits superconductivity by interfering with the formation of Cooper pairs. Most R ions substitute into an isostructural series with no observable effect on the superconducting properties of the material. As can be seen from Table 1, there are notable exceptions to this observation. In particular, the rare-earth ions Ce, Pr, and Tb, together with the 5f-actinide ions Am and Cm, sometimes behave anomalously. These ions either do not form an isostructural phase, or if the phase forms it may not be superconducting. The fact that an f-ion can suppress superconductivity is clearly demonstrated in the isostructural series Y{sub 1{minus}x}Pr{sub x}Ba{sub 2}Cu{sub 3}O{sub 7} (0 < x < 1){sup 3}, in which the critical temperature decreases with increasing x, such that for concentrations of Pr greater than x {approx} 0.5, the samples no longer superconduct.
- Research Organization:
- Argonne National Lab., IL (US)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- W-31109-ENG-38
- OSTI ID:
- 10976
- Report Number(s):
- ANL/CHM/CP-97337
- Country of Publication:
- United States
- Language:
- English
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