Preparation, structure, and electrical properties of Ca1-x Er x MnO3 powders

To improve the electrical properties of modified CaMnO3 powders, we synthesized Ca1-x Er (x) MnO3 (CEM) (0 a parts per thousand currency sign x a parts per thousand currency sign 0.3) powders by sol-gel autocombustion technology. The effects of the Er-doping concentration on the structure and electrical properties of the powders were studied. The results show that Er-doping can decrease the resistivity of the CEM powders effectively and the variation of the resistivity presents a typical V-type with increasing Er-doping concentration. The resistivity reaches the lowest point of 0.5258 Omega m at x = 0.25. Meanwhile, the Ca0.75Er0.25MnO3 powder showed good frequency stability and higher conductivity at high temperatures. x-Ray diffraction (XRD) patterns and valence analysis illustrate that the grain size and average valence of the Mn ions, which relate to the resistivity of the CEM powders, are affected by the Er-doping concentration. When x = 0.25, the average valence of the Mn ions reaches the lowest point of 3.576. Scanning electron microscopy (SEM) analysis demonstrates that higher Er-doping concentration leads to smaller grain size in the CEM powders. Er-doping restrains the growth of the powder particles while decreasing the porosity and increasing the unit cell volume, resulting in improvement of the electrical properties of the modified powders.