DEPENDENCE OF SUPERCONDUCTING TRANSITION-TEMPERATURE ON DOPING AND STRUCTURAL DISTORTION OF THE CUO2 PLANES IN LA(2-X)M(X)CUO(4) (M=ND,CA,SR)

By comparing structural and superconducting properties of La2-x-yCaxNd yCuO4 to La2-xSrxCuO4 we have separated the effects of structure and d oping on the superconducting T-c. At a fixed doping level, the highest T-c is found for flat and square CuO2 planes in the tetragonal struct ure. T-c is reduced by the structural distortions of the CuO2 planes i n the orthorhombic structure. The local minimum of T-c vs doping obser ved around x similar to 0.12 indicates the presence of a weakly split singularity of the electronic density of states for the orthorhombic m aterial.