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.
Extraction of the fine structure from x-ray absorption spectra
We propose two methods for obtaining the atomic-like background for the x-ray absorption fine structure (XAFS): the methods of smoothing spline and of Bayesian smoothing. Both are capable of using the prior information, calculated or experimental, about the background. The XAFS signals obtained by these techniques are shown to be significantly corrected in comparison with standard methods. The method of Bayesian smoothing is the only method that gives the errors of approximation of the atomic-like background by an artificial smooth function. These errors are shown to be the main source of the uncertainty of the XAFS function.
Electron Irradiation Effects in a BiPbSrCaCu Oxide Superconductor
Electron irradiation effects on the superconductive properties of Bi0.7Pb0.3SrCaCu1.8Oy are in-vestigated. The samples are irradiated with 7 MeV electrons in air, liquid nitrogen, and water. In case of irradiation in air, the transition temperature Tc is shifted to lower temperatures with a degradation rate of 5 K/1019e/cm2, and the resistivity in the normal state increases with 0.7 mΩ cm/1018 e/cm2. The susceptibility-temperature curves are also shifted to lower temperatures along the temperature axis, but there is no appreciable change in the absolute susceptibility for irradiations up to 3.6 × 1018 e/cm2. The critical current density Jc decreases slightly for the irradiation in air. The degradation of the samples irradiated in liquid nitrogen is similar to that in air. The degradation of the samples irradiated in water is significant, but the superconductive properties are not lost completely with an electron irradiation dose of 1 × 1018 e/cm2. 
 
 
 
Bestrahlenseinflusse auf den Supraleiter Bi0.7Pb0.3SrCaCu1.8Oy wurden mit Hilfe von 7-MeV-Elektronenbeschus in Luft, in flussigem Stickstoff und in Wasser untersucht. Im Falle der Bestrahlung in Luft verschiebt sich die Supraleitungsubergangstemperatur Tc zu niedrigeren Tem-peraturen mit einer Degradationsrate von 5K/1019 Elektronen/cm2, und der Widerstand fur den Normalzustand nimmt mit einer Rate von 0,7 mΩcm/1018 Elektronen/cm2 zu. Die Suszeptibilitats-Temperaturkurven verschieben sich zu niedrigeren Temperaturen, jedoch tritt keinemerkliche Anderung der absoluten Suszeptibilitat bis zu 3,6 × 1018 Elektronen/cm2 auf. Der kritische Strom Jc fallt leicht ab fur Bestrahlung in Luft. Die Degradation der Proben in flussigem Stickstoff ist der in Luft ahnlich. Die Degradation der Proben fur Bestrahlung in Wasser ist gros, jedoch geht die Supraleitfahighkeit nicht restlos bei einer Elektronenbstrahlungsdosis von 1 × 1018 Elektronen/cm2 verloren.