|| Checking for direct PDF access through Ovid
The TlSr2(Ca1−xRx)Cu2O7 (Tl-1212) phase with R=Dy, Tb and Ho for x=0.1–0.6 has been studied by powder x-ray diffraction method and electrical resistance measurement. All the samples showed a metallic normal state behavior. No correlation between ionic radius and Tc onset is observed. The three series show the highest volume fraction (>97%) of Tl-1212 phase for x=0.5. The highest Tc onset does not correspond to the highest volume fraction. The above results are explained as due to the mixed valence state of Dy and Tb in the Tl-1212 phase.