Studies Of Preparation And Electrical Properties Of CuAlO₂ Modified By Cation Doping

There are two kinds of semiconductor coatings used in the spark plug: SiC-based and Cu2O-based materials which is usually used in domestic. Nowadays, for solving the problems of instability quality because of the lower domestic technical level, a research about CuAlO₂ as semiconductor coating of the spark plug is proposed. However, the electrical conductivity of CuAlO₂ is small, which causes the ignition voltage of the CuAlO₂-based material much higher than that of Cu2O-based. So it is urgent to improve the electrical conductivity of CuAlO₂. In the paper, Cu Al O2 was the object of study, and CuAlO₂-based ceramics were prepared by the solid state oxide reaction method. The structure and electrical properties of CuAlO₂-based ceramics were investigated, which is in order to obtain a higher electrical properties of CuAlO2.At the first, for obtain a higher electrical conductivity, the effect of Cu Al1-xCrxO2 ceramics with different Cr2O3 content on structure and electrical properties were investigated. The results shows that CuAlO₂ and Cu2 O are formed in samples. The Cu cations in CuAlO₂ lattice exist two states: Cu + and Cu2 +. With the increase of Cr content, the conductivity of the samples shows a decreasing trend after the first increase. The factors of electrical conductivity are mainly the Cu valence distribution and carrier mobility. The ignition voltage of coating shows a gradual decreasing trend with the increased Cr content.Secondly, the Sc2O3 added CuAlO₂ ceramics were prepared by the solid state oxide reaction method. The research shows that all samples are delafossite structure. The samples have impurity phase CuO whose content increases with increased Sc2O3 content. Electrical impedance spectroscopy shows that there only exists one carrier species, which is thermally activated and controls the relaxation and conduction. T he carrier mobility ? increases monotonously while the carrier density n stays at a certain level for suitable Sc2O3 addition, thus leading to the increase of the n×?. The tendency of conductance is similar with that of the n×? of Sc2O3 added CuAlO₂. When y=0.09, the electrical conductivity is 2 orders of magnitude higher than that of CuAlO₂. The Sc2O3 doping can decrease the ignition voltage of samples. And with the increasing Sc2O3 content, the ignition voltage have a decreasing trend after the first increaseAt last, the CuAl_1-z Y_zO₂ ceramics were prepared, and the structure and electrical properties of ceramics were discussed in detail. The results show that the most of the Y3+ enter into the CuAlO₂ lattice to occupy Al3+ sites, while the second phase Al5Y3O12 is formed due to the limited solubility of Y2O3 into CuAlO₂. The electrical conductivity decreases?z=0⁰.03?, followed by an increase?z ? 0.04? with the increase Y2O3 content. The Hall Effect measurement reveals the carrier mobility increases with the Y2O3 added. The variation of the carrier mobility and microstructure could exactly explain the dependence of electrical conductivity of CuAlO₂ with Y2O3 increase: the insulated Al5Y3O12 controls the conductivity when small Y2O3 is added, and the rapid growth of carrier mobility becomes the predominant when Y2O3 addition exceeds over z = 0.04. The ignition voltage of CuAl_1-z Y_zO₂ cocating with the increased x decreases and then increases. The result with Y2O3 doping is better than that of Sc2O3 doping.