Influence of ZnO and TiO₂ additions on structural, physical, and electrical properties of LaCo_0.3Mn_0.7O₃ perovskite

Lanthanum manganite-lanthanum cobaltite (LaCo_0.3Mn_0.7O₃) solid solutions have been investigated as potential candidates for ceramics, catalysts, and sensors. A microwave hydrothermal process was used to prepare LaCo_0.3Mn_0.7O₃ powders, fired at temperatures of 600, 1100, and 1300 °C. The effect of different transition metal additions (ZnO and TiO₂) on the optimum selected perovskite was studied. X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), bulk density, apparent porosity, and electrical, mechanical, and magnetic properties were used to characterize the obtained materials. The results indicated that the optimum perovskite phase was obtained at 1100 °C. Different amounts of ZnO and TiO₂ did not react with the perovskite, which was a separate phase. The maximum density of about 4.55 g/cm³ was observed for the sample containing 10 wt% of TiO₂, and a minimum porosity of about 2.5% is obtained for the sample containing 20 wt/% of TiO₂, While the bulk density reached 5.7 g/cm³ and porosity of about 2% after the addition of 30 wt% of ZnO. ZnO enhances the sinterability, hardness, and conductivity of perovskite structure. On the contrary, TiO₂ was added up to 20 wt% enhances hardness properties, while the conductivity is decreased by TiO₂ addition. The hardness value reaches 6.76 in the case of 20 wt% TiO₂ and 5.6 in case of 30 wt% ZnO addition. This is due to the formation of a large amount of the liquid phase, which acts as a barrier to charge transfer. The electrical properties of the LaCo_0.3Mn_0.7O₃ matrix with varying TiO₂ and ZnO contents, sintered at 1100 °C, were investigated through conductivity and resistivity measurements at 28 °C, 100 °C, 300 °C, and 500 °C. Upon increasing the TiO₂ content from 10 to 30 wt% resulted in increased resistivity from 1.5 × 10⁸ to 3.3 × 10⁸ Ω cm and decreased conductivity from 6.5 × 10^-9 to 3.5 × 10^-9 S/cm. Conversely, increasing the ZnO content increased the conductivity from 3.5 × 10^-9 to 6.3 × 10^-9 S/cm and decreased the resistance from 2.85 × 10⁸ to 1.5 × 10⁸ Ω cm. In addition, all samples exhibited paramagnetic properties that decreased with the addition of transition metals.