Doping effect on the electrical properties of amorphous Al2O3

Thermal and electrical properties for pure and doped amorphous Al2O3 (by 1% Fe3+, Ni2+, Co2+) have been investigated. All samples changed to γ-Al2O3 after annealing at 1200 K for 3 h. Electrical conductivity σ, dielectric constant ε′ and dielectric loss ε″ were studied between 78 and 400 K and over a frequency range of 0–106 Hz. An anomalous behavior in ln σ–T−1 relation is observed for all samples. σ-value increases in the order: σCo-doped>σNi-doped>σFe-doped>σpure. At lower temperatures, semimetallic behavior was observed; while at moderate temperatures semiconducting behavior predominates with an activation energy decreases with the addition of the doping ions. The ac-conductivity was found to obey the power relation σ(ω)=Aωs. ε′-value increased in the order: εCo-doped′>εNi-doped′>εFe-doped′>εpure′. Both ε′ and ε″ showed maximum values at temperatures which are not changed by measuring frequencies. These maxima are slightly shifted to lower temperatures by adding the doping ions. The results have been discussed on the basis of the formation of AlO dangling bonds in each of the pure and the doped Al2O3.