HOLE DENSITY AS EVIDENCED BY XAS AND CRITICAL-TEMPERATURE IN THE TLBA2CA1-XNDXCU2O7-DELTA SERIES

To estimate the variations of the doping hole density in a series of thallium cuprates, TIBa2Ca1-xNdxCu2O7-δ with the substitution amount x, we used XAS at the copper L3-edge. The spectra were recorded on powder samples with the total electron yield method. From the simulations of the spectra with two pseudo-Voigt functions, the |;3d9L> relative intensity, with respect to the |3d9> one, has been calculated and compared to the variations of Tc's and to the copper formal charge deduced from previous neutron diffraction experiments. A correlation between the doping hole density in the [CuO2]∞ planes, nh(x, y), and Tc's has been clearly established. The difference between the copper formal charge as deduced from neutron diffraction and the equivalent one deduced from our experiments has been assigned to extra holes likely located in the 2pz orbitals of the apical oxygen of the copper square pyramids. © 1992.