Abstract
The effect of cadmium substitution for gallium on the phase stability and superconducting properties of Ga-based 1212, (Ga
1−
x
Cd
x
)Sr
2(Y
1−
y
Ca
y
)Cu
2O
7; was investigated. X-ray diffraction revealed that Cd is soluble in the Ga-site up to
x
=
0.6. Cd
2+ substitution for Ga
3+ induces an orthorhombic-tetragonal phase transition around
x
=
0.35. Some sign of superconductivity appears in Cd-substituted samples with
x
⩾
0.4, without Ca doping at Y-site;
y
=
0.0. Superconducting properties are improved by co-substitution of Cd
2+ for Ga
3+ and Ca
2+ for Y
3+. Both onset and zero
T
c’s increase with increasing Cd concentration and the superconducting transition width becomes more sharp. The highest onset
T
c is 65
K for the sample with nominal composition of (Ga
0.4Cd
0.6)Sr
2(Y
0.7Ca
0.3)Cu
2O
7.