The Influence of Mobile Holes in Hg 1 − x Pb x Ba 2 Ca 2 Cu 3 O 8 + δ Superconductors

Abstract

By means of X-ray diffraction (XRD), neutron diffraction spectra (NDS), electron probe microanalysis (EMPA), and X-ray photo electron spectroscopy (XPS) etc., we studied the superconductivity of doped-Pb Hg-1223 compound. The crystal parameters a and c and the unit cell volume of the Pb-doped sample do not change considerably, but the intercalated O(4) of the sample increases more than that of the pure-phase Hg-1223. As for the valence number of Hg is still 2 and that of Pb is either 2 or 4, the bond length of Cu(2)–O(3) increases, Raman frequency of the AIg mode of the apical O(3) increases, the bond angle of O(2)–Cu(2)–O(2) is smaller and the hole density is approximately uniformly shared between the three CuO2 planes. The above have been affirmed by our experiment data and calculations based on Bond Valence Sums (BVS). Thus, the enhancement in Tc of the Pb doping effect is due to the variation of the electronic state and its distribution.