Crystal Structure, Oxygen Content and Superconductivity of MxLa2-xCuO4-y (M=Ba, Sr and Ca)

Unit cell dimensions, oxygen vacancy y, and superconducting properties of M x La2-x CuO4-y (M=Ba, Sr and Ca) with K2NiF4 structure have been determined by means of X-ray powder diffraction, thermogravimetry, and electrical resistivity measurements. The existence percentage of Cu as Cu3+, P=(Cu3+/Cu)%, was estimated from the measured y values on the basis of charge neutrality. The superconducting critical temperature, T c, is discussed in terms of the P value and Cu-O bond length within the basal plane. Composition dependence of the unit cell dimensions is discussed by taking the P value and the ionic radii into consideration.