Synthesis of New Pb-Based 1222 Cuprates Containing Phosphorus, (Pb0.75P0.25)Sr2(RE2–x–y Ce x Sr y )Cu2O z (RE = Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Y)

New Pb-based 1222 cuprates containing phosphorus have been synthesized in the (Pb_0.75P_0.25)Sr₂- (RE_2–x–y Ce _x Sr _y )Cu₂O _z (RE = Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Y) systems. The almost-single phase samples are obtained for 0.5≤x≤1.0 and y=0.1 in the cases of RE = Nd, Dy, Ho, Er, Tm, Yb and Y, while for 0.3≤x≤1.0 and y=0.1 in the cases of RE = Sm, Eu and Gd. The samples crystallize in a tetragonal lattice, the lattice parameters a and c are decreasing with the decrease of the ionic radius of the RE element. Even after annealing under 143 atm O₂ atmosphere at 400 °C, almost all the samples with the common values x=0.5 and y=0.1 are semiconductors with a transport process followed by three-dimensional variable range hopping. However, the samples of RE = Sm, Eu and Gd, which are of almost single 1222 phase, even for x=0.3 and y=0.1, show superconductivity with the onsets at about 25 K, 20 K and 22 K, respectively. Through this study, we find very important procedure for discovery of new superconducting 1222 compound.