Structural and transport properties of the La1.85Sr0.15Cu1−xMxO4 superconducting system

X-ray diffraction and resistivity measurements were carried out on La1.85Sr0.15Cu1−xMxOy (La: 214) ceramic samples with different doping elements M and doping contents x (M = Li, Ni, Co and Mn, and x = 0.00,0.15 and 0.30). It is found that the substitutions of the above dopants at Cu sites cause lattice deformation and lead to the largest change in the transport properties of La: 214 systems. The pure sample with x = 0.00 exhibits superconductivity at 36 K, while the samples with x = 0.15 and 0.30 show semiconductor-like behavior with decreasing temperature from 300 K down to 20 K. The magnetic doping samples show a rapid increase in the resistivity more effectively than samples with the nonmagnetic dopants. The rate of increase in the resistivity with doping follows the order Mn>Co>Ni>Li. On the other hand, the activation energy Ea is calculated in the three different temperature regions characterized in the (ρ–T) curve. A good correlation in the behavior of Ea as well as resistivity with dopants is reported. Our data fit well with the Arbrikosov and Gork’ov theory, but disagree with those of Huang et al (2005 Physica C 421 56). Our comments on Huang et al’ s samples are reported.