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تسجيل مستخدم جديدMechanism and kinetics of phase formation of cobalt oxyhydrates (Na,K)x(H2O)yCoO2-delta synthesized using aqueous permanganate solution route
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This paper has been withdrawn by the author due to a data error in Fig 5.
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We have first succeefully synthesized the sodium cobalt oxyhydrate superconductors using KMnO4 as a de-intercalating and oxidizing agent. It is a novel route to form the superconductive phase of NaxCoO2.yH2O without resorting to the commonly used Br2
/CH3CN solution. The role of the KMnO4 is to de-intercalate the Na+ from the parent compound Na0.7CoO2 and oxidize the Co ion as a result. The higher molar ratio of KMnO4 relative to the sodium content tends to remove more Na+ from the parent compound and results in a slight expansion of the c-axis in the unit cell. The superconducting transition temperature is 4.6-3.8 K for samples treated by the aqueous KMnO4 solution with the molar ratio of KMnO4 relative to the sodium content in the range of 0.3 and 2.29.
We have first used the aquesous KMnO4 solutions to de-intercalate and oxideze gamma-phase of Na0.7CoO2 and successfully form the superconductive phase of cobalt oxyhydrate hydrates (Na,K)xCoO2.yH2O with Tc=3.2-4.6K based on the magnetization measurem
ents. The higher molar ratio of KMnO4/Na used to treat Na0.7CoO2 results in more removal of Na+ and leads to a partial or even complete replacement of K+ for Na+. The low molar ratio of KMnO4/Na forms a superconductive phase with the c-axis ca. 19.6 angstrom, whereas the high molar ratio of KMnO4/Na forms a non-superconductive phase with teh c-axis ca. 13.9 angstrom. The superconductive 19.6 angstrom phase is unstable with respect to the ambient air in terms of losing water molecule from the structure; nevertheless, the dehydration/hydration process is reversible when storing the sample in a chamber with sufficient humidity.
The existence of two phases within one and the same hexagonal lattice of MgB2 compound, differing in Mg and B (in the homogeneity region) and especially in impurity oxygen content, as well as in microstructure, is demonstrated by various techniques.
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