Effect of A-site cationic radius on polycrystalline ceramics La x Sm0.67−x Sr0.33MnO3 prepared by sol–gel technique

Abstract

In this paper, polycrystalline ceramics LaxSm0.67−xSr0.33MnO3 (x = 0.00, 0.10, 0.20, 0.25, 0.30, 0.365, and 0.40) were prepared by sol–gel technique. The structure was tested by X-ray diffraction, which shows that all samples are single phase, but the progressive substitution of Sm3+ by La3+ enlarges the volume of the unit cell. The surface morphology was investigated by scanning electron microscope, which indicates that the samples with better crystallization have higher density. The electrical property was measured by the standard four-probe method, which demonstrates that the resistivity decreases and the metal–insulator transition temperature shifts to higher temperature with increasing La content. Furthermore, the progressive substitution of Sm3+ by La3+ broadens the metal–insulator transition and reduces the temperature coefficient of resistivity. A mechanism based on double exchange is proposed to interpret the results above.