EXAFS study of Tl₀.₇₅Cu.₂₅Ba₂Ca₃Cu₄ Oy and Cu₀.₆₈C.₃₂Ba₂Ca₃Cu₄ Oy superconductors [bulk] at 300 K

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The results of EXAFS measurements at 300 K for the superconducting compounds Tl₀.₇₅Cu₀.₂₅Ba₂Ca₃Cu₄Oy [Tl-1234], TlBa₂Ca₃Cu₄Oy [Tl-1212], and CuBa₂Ca₃Cu₄Oy [Cu-1234]. are reported. We have measured the EXAFS spectrum for Tl₀.₇₅Cu₀.₂₅Ba₂Ca₃Cu₄Oy in the range 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 with small carbon concentrations and exhibits a Tc of 127 K. We have also performed ``aging'' study by looking at XRD for this material after approximately one year. The XRD results at 300 K are ``unchanged''. It is of interest to compare the EXAFS spectrum of this compound with the corresponding compound Cu-1234. Remarks on the choice of appropriate EXAFS standard for this and related compounds are also given. Based on our data analysis we quantify disorder in these systems. By using the Cu-O in-plane distance we give values for the microstrain parameter, which can be related to the charge ordering transition.