Local structure of nanopowders of refractory nitrides used to increase the critical current of high-temperature superconductors
The effect of dispersivity on the local-structure features in ZrN nanocrystals has been investigated by X-ray absorption (EXAFS) spectroscopy. The Debye-Waller factors and bond lengths have been determined for Zr-N and Zr-Zr coordination spheres. It is found that a decrease in the nanoparticle size leads to an increase in the static Debye-Waller factor for the Zr-Zr bond. The scale of changes is comparable with the increase in the Debye-Waller factor upon heating from 15 to 77 K.
Role of the perovskite-like lattice in the high-temperature superconductor mechanism: EXAFS data analysis
The temperature-dependent extended X-ray absorption fine structure (EXAFS) spectra of hole- and electron-doped high-temperature superconductors (La2 − xSrxCuO4 and Nd2 − xCexCuO4 − δ, respectively) are investigated above the CuK absorption edge. It is demonstrated that, for superconducting compounds (x = 0.15), the part of the oxygen ions in the CuO2 plane oscillates in the double-well potential, and their oscillations are correlated with the charge-carrier transport. The presented data indicate the direct relation between the experimentally observed local dynamic structural inhomogeneity and the local dynamic charge ordering. A phenomenological description of the correlation between the local electronic and local crystalline structures, which enables us to reveal the role of collective oxygen-ion oscillations inherent to the perovskite-like lattice in the establishment of the superconducting state in doped La2CuO4 and Nd2CuO4, is proposed to explain the experimental results.
Finite Difference Modeling on the Temperature Field of Substrate in Friction Surfacing
Friction surfacing is an advanced process of great potential, especially in the field of repair and reclamation of worn and damaged components. As a kind of thermal processing technology, the temperature profile and changes of the substrate in friction surfacing are important factors to get coatings of high quality. In this paper, the temperature field of the substrate during the process is simulated by finite difference method. The results are consistent with experiments, reappearing the temperature change of the substrate during friction surfacing, allowing further study on figuration and quality of coatings.