Incommensurate modulation in the high-Tc superconductor Ba1−xKxBiO3 and its relation to the conducting properties
M. Verwerft, G. Van Tendeloo, D. G. Hinks, B. Dabrowski, D. R. Richards, A. W. Mitchell, D. T. Marx, Shiyou Pei, J. D. Jorgensen
DOI 10.1103/PhysRevB.44.9547 · Physical Review B
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Abstract
The incommensurate modulation in Ba1−xKxBiO3 is studied by means of electron diffraction. Attention is paid to the symmetry of the modulation and the effect of electron irradiation. Interpretation of the modulation symmetry in cubic samples (0.3<x<0.5) as well as in orthorhombic samples (0.1<x<0.3) in the framework of a four-dimensional description allows one to determine it as a periodic displacement of the bismuth atoms. Satellite reflections corresponding to the modulation are observed only after irradiation with electrons. However, since the critical voltage is below 40 kV, it is believed that the modulation is in fact a fundamental material property. The incommensurability of the modulation for x<0.4 results in a partial charge disproportionation on the bismuth sites, which can explain the lack of superconducting properties for Ba1−xKxBiO3 with x<0.4. In the superconducting phase Ba0.6K0.4BiO3, the modulation is commensurate, and high-resolution observations provide evidence for a modulation model without charge disproportionation, yielding a metallic behavior at room temperature.
Source-reported materials — not catalogue approval
| Formula | Reported Tc (K) | Pressure (GPa) | Type |
|---|---|---|---|
| Ba0.6K0.4BiO3 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 30 | Pressure not reported | unknown |
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