Abstract
The low-temperature properties of strongly depend on its thermodynamic state established via thermal treatment. We present high resolution x-ray powder diffraction data taken on a pair of polycrystalline samples with identical chemical composition but annealed at different temperatures, namely, at 800 and at 1100 °C. Their superconducting transition temperatures differ by more than 10%. Rietveld refinement and difference Fourier analysis reveal subtle differences in the atomic parameters and in the electron density on the carbon site. Furthermore, a new atomic site can be identified for both samples, which is partially occupied with the lighter atoms boron or carbon.
- Received 30 August 2000
DOI:https://doi.org/10.1103/PhysRevB.63.184518
©2001 American Physical Society