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Abstract-Nanocrystalline sensors having the general formula ZnO + x wt% CeO 2 , where x = 0, 2, 4 and 6 were prepared by chemical precipitation method and sintered at 400, 600 and 800 o C for 2h in static air atmosphere. The crystal structure and the morphology of the prepared samples were investigated and characterized by using XRD, IR, SEM and TEM techniques. The investigation revealed that the average crystallites size increases with increasing the sintering temperature. The electrical conductivity is found to increase with CeO 2 additions and sintering temperature. Gas sensing properties of the prepared samples were also investigated. The effect of CeO 2 content and sintering temperature on the structure, electrical conductivity and ethanol gas sensing properties of the prepared samples are discussed.

U0 3 / Electrical conductivity/ U0 3 modifications / Activation energy SummaryThe crystalline U0 3 phases α, β, y, δ, ε as well as an amorphous sample were prepared. The electrical conductivity was measured from 25 up to ~480°C for the different phases of U0 3 in air. The variation of conductivity at constant temperature from phase to phase was related to the variation of crystal structure and lattice defects. Generally, the conductivity showed a positive temperature coefficient. The intrinsic energy gap Δ E was found to be 2.52 or 2.68 eV for different investigated samples. The temperature range of intrinsic region depended on the nature of the phases. The decomposition temperature of the U0 3 samples was reflected on the conductivity curve as hump, peak or plateau.

The a.c. conductivity as a function of temperature was measured for ten prepared samples. The measurements were carried out in the temperature range 25–340°C. The sample CuMn2O4 prepared either from oxide or carbonate contains the least impurity content, while the sample Cu1.5Mn1.5O4 from oxide origin and Cu1.6Mn1.4O4 from carbonate origin contain the highest impurity content. The activation energy ΔE1 values for the oxide origin samples are nearly the same of those obtained from carbonate origin. The variation of ΔE2 values with concentration of copper content (x) appears to be consistent.