Effect of la³⁺ substitution for sr²⁺ on the phase formation, structure and properties of (t1_{0 5}pb_{0 5})sr₂ca₂cu₃o_y compounds

Optimization of the hole concentration in (Tlj.sPhJSrjCfljDijOj (Tl1223) was attempted though partial replacement uf SrK by I,a 3l Nine sample with nominal composition (TlPboOS'VïlACajCiijOj, were prepared, with X varies from 0 to I. Magnetization measurements as a function of temperature showed t lint the transition tcmpcnilnrc increased with increasing La content. These measurements also showed an increase of the dtaniagnctK1 signal as L:i was increased. Xray (infraction patterns uf the samples showed Hint Ln addition improved the phase purity of TI12I3 for low level La substitution (l <, 0,03). Formation of impurity phases and a phase transformation were also observed tor high La contents. Tlic microstructurc appearance of the samples with different I,a content was different. Samples with x values 0.5, I and 2, were very brittle and the pellets dissociated into line powder in one week time. These results will be discussed in terms of changes in the charge carrier concentration In the CuO planes of the originally overdopcd '111223 high temperature superconductors.