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The structure and electronic transport properties have been investigated for composite PbO2-1/12Ag(2)O-xC (0 less than or equal to x less than or equal to 2) materials prepared by mechanical milling in an O-2 atmosphere. The solid-state reactions result in the occurrence of abundant phase transformations, when the graphite content increases. With the phase transformations occurring, the percolation effect is observed for the electronic transport of PbO2-1/12Ag(2)O-xC system, while its conductivity undergoes an insulator-metal transition. The percolation threshold is determined by DC conductivity measurement and analysis of X-ray diffraction patterns. (C) 2003 Elsevier Science Ltd. All rights reserved.