Nm. Hamdan et al., Effect of La3+ substitution for Sr2+ on the phase formation, structure andproperties of (Tl0.5Pb0.5)Sr2Ca2Cu3Oy compounds, IEEE APPL S, 10(1), 2000, pp. 1174-1177
Optimization of the hole concentration in (Tl0.5Pb0.5)Sr2Ca2Cu3Oy (Tl-1223)
was attempted though partial replacement of Sr2+ by La (3+). Nine sample w
ith nominal composition (Tl0.5Pb0.5)Sr2-xLaxCa2Cu3Oy were prepared, with x
varies from 0 to 2. Magnetization measurements as a function of temperature
showed that the transition temperature increased with increasing La conten
t. These measurements also showed an increase of the diamagnetic signal as
La was increased. X-ray diffraction patterns of the samples showed that La
addition improved the phase purity of Tl-1223 for low level La substitution
(x less than or equal to 0.03). Formation of impurity phases and a Phase t
ransformation were also observed for high La contents. The microstructure a
ppearance of the samples with different La content was different. Samples w
ith x values 0.5, 1 and 2, were very brittle and the pellets dissociated in
to fine powder in one week time. These results will be discussed in terms o
f changes in the charge carrier concentration in the Cu-O planes of the ori
ginally overdoped Tl-1223 high temperature superconductors.