Dependence of lattice parameters and Tc on the hole concentration determined by precise measurement of the oxygen content of MxLa2-xCuO4-y (M = Ba, Sr, Ca)

Systematic precise measurements of oxygen content have been performed on sintered samples of MxLa2-xCuO4-y (M = Ba, Sr, Ca) superconducting oxides by both thermogravimetry and iodometry. The hole concentration, P, has been estimated by using the obtained oxygen content on the basis of charge neutrality. Lattice parameters and superconductivity of the samples have been measured by X-ray powder diffraction analysis and electrical resistivity or ac magnetic susceptibility measurement, respectively. The lattice parameter, a, depended, on both P and the average ionic radius of the La3+ site and c depended on the average ionic radius of the La3+ site, volume compensation, and oxygen defect. Orthorhombicity (defined by 2(b-a)/(a+b)) depended on P. Superconductivity appeared at the same hole concentration, P = 0.10, regardless of the kind of alkaline-earth metal used. A linear relation between Tc and Cu-O1 bond length within the basal plane in the structure was recognized only in the case where the hole quantity, P, was constant