EXAFS study of Tl$_{0.75}$Cu$_{.25}$Ba$_2$Ca$_3$Cu$_4$ O$_y$ and Cu$_{0.68}$C$_{.32}$Ba$_2$Ca$_3$Cu$_4$ O$_y$ superconductors [bulk] at 300 K

摘要

The results of EXAFS measurements at 300 K for the superconducting compoundsTl$_{0.75}$Cu$_{0.25}$Ba$_{2}$Ca$_{3}$Cu$_4$O$_{y}$ [Tl-1234],TlBa$_{2}$Ca$_{3}$Cu$_{4}$O$_{y}$ [Tl-1212], andCuBa$_{2}$Ca$_{3}$Cu$_{4}$O$_{y}$ [Cu-1234]. are reported. We have measured theEXAFS spectrum for Tl$_{0.75}$Cu$_{0.25}$Ba$_{2}$Ca$_{3}$Cu$_4$O$_{y}$ in therange 10K-300K, however here we limit our discussion to the spectrum at 300 K.This material is prepared under high pressure [3.5 GPa] from precursors withsmall carbon concentrations and exhibits a T$_c$ of $~127$ K. We have alsoperformed ``aging'' study by looking at XRD for this material afterapproximately one year. The XRD results at 300 K are ``unchanged''. It is ofinterest to compare the EXAFS spectrum of this compound with the correspondingcompound Cu-1234. Remarks on the choice of appropriate EXAFS standard for thisand related compounds are also given. Based on our data analysis we quantifydisorder in these systems. By using the Cu-O in-plane distance we give valuesfor the microstrain parameter, which can be related to the charge orderingtransition.