Structure and physical properties of NaxCoO2.yH2O superconducting system
Y.G. Shi, J.Q. Li, H. C. Yu, Y. Q. Zhou, H. R. Zhang, C. Dong
TL;DR
This study investigates the structural and electronic properties of NaxCoO2 and its hydrated superconducting form, revealing superstructures, valence states, and compositional details related to its superconductivity at around 3.5K.
Contribution
It provides detailed structural, compositional, and electronic characterization of NaxCoO2 and its hydrated superconducting phase, highlighting changes associated with superconductivity.
Findings
Superconducting transition at ~3.5K in hydrated samples
Superstructure observed in parent compound, weakened in superconductors
Co valence state increases from +3.3 to +3.7 in superconducting phase
Abstract
The structural properties of NaxCoO2 and NaxCoO2yH2O have been investigated. The NaxCoO2yH2O samples in general show up the superconducting transitions at around 3.5K. EDAX analyses suggest our samples have the average composition of Na0.65CoO2 for the parent compound and Na0.26CoO2yH2O for the superconducting crystals. TEM observation reveals a superstructure with wave vector q=<1/2,0, 0> in the parent Na0.65CoO2 materials. This superstructure becomes very weak in the superconducting oxyhydrates. EELS analyses show that the Co ions have the valence state of around +3.3 in the Na0.65CoO2 materials and around +3.7 in the superconducting materials.
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