Metal-nonmetal transition and the electronic transport behavior in disordered PbO2-Ag2O-xC system synthesized by ball milling

The electronic transport properties as a function of temperature and the graphite content have been investigated for disordered PbO2-Ag2O-xC (0 ≤ x ≤ 3) composite materials. The components of the system change from (1) lead-silver oxides of Ag5Pb2.5O6 and/or Ag2PbO2 to (2) PbCO3 + 2PbCO3·PbO + Ag and (3) PbCO3 + Ag + Pb with increasing the graphite content. Ag5Pb2O6 is synthesized directly by mechanical milling with a simple solid-state reaction of Ag2O and PbO2. The structure, thermal and electric properties of silver-lead oxides are characterized by means of X-ray diffraction, scanning electron microscope, a differential scanning calorimeter analysis and DC resistivity measurements. Strengthening the degree of disorder through mechanical milling and/or doping the lead oxide into Ag5Pb2O6 causes the conductivity transition from metallic to semiconducting behavior, while decreasing the degree of disorder by annealing and the segregation of the lead oxide from the solid solution leads to a reverse transition. C 2005 Springer Science + Business Media, Inc.