Possibility of decreasing the activation energy of resistivity of mullite by doping with nickel ion

Monophasic mullite samples doped with 0.002 M, 0.02 M, 0.1 M, 0.15 M and 0.2 M of NiCl2 were prepared via sol-gel technique. The prepared gels were dried, grinded, pressed into pellets and sintered at 400 °C, 800 °C, 1000 °C and 1300 °C. The electrical resistivity and activation energy of the composites have been measured and the variation of resistivity with concentration of the nickel ion doping has been investigated. The resistivity decreases with the concentration of nickel ions. X-ray analysis confirms the presence of Ni2+ ions in mullite. The Ni2+ ion, which substitutes Al3+ ion in the octahedral site of mullite structure, can be considered as an efficient factor in reducing the resistivity. The mullite unit cell parameters suggest predominant incorporation of NiCl2 in a glassy phase. The lowest activation energy of resistivity (E act) that was achieved is 1.22 eV at 0.02 M.