La-site substitution effect by Ce ion on carrier concentration and structural phase transition in La2-xSrxCuO4

We have studied an effect of the partial substitution of Ce4+ ion for La-site on the superconductivity and the structural phase transition between the high-temperature tetragonal (HTT) and the low-temperature orthorhombic (LTO) phases in La2-xSrxCuO4. For La2-xSrxCuO4 without substitution by Ce ion, x dependence of the critical temperature Tc showed a dip at x 0.115 and a maximum at x = 0.15. The dip structure shifts to x = 0.125 and the Tc maximum shifts to x = 0.16 for La1.99-xSrxCe0.01CuO4. On the other hand, x dependence of the structural phase transition temperature Td1 was hardly affected by the Ce substitution. These results indicate that the Ce substitution for the La-site gives a possibility to realize the flatter CuO2 planes without the change of the carrier concentration.