Effect of Ca-doping on the electrical properties of La0.2Nd0.47Sr0.33MnO3 ceramics prepared by sol–gel technique

A series of ceramic samples La0.2Nd0.47Sr0.33−x Ca x MnO3 (x = 0.00, 0.03, 0.06, 0.09 and 0.12) were prepared by sol–gel technique. The crystal structure was analyzed by X-ray diffraction, which reveals that all the samples are single-phase without any detectable secondary phases. The grain size and surface morphology were investigated by scanning electron microscope ,which indicates that ceramic samples with better crystallization have high density. The resistivity dependence of the temperature (R-T) of the bulk samples was studied by the standard four-probe method. The result of the R-T curves shows that the metal-insulator transition temperature shifts to the lower temperature and the resistivity as well as the maximum value of the temperature coefficient of resistivity increase. It is usually interpreted as the Ca-doping decreases the A-site cationic radius and the tolerance factor, which results in MnO6 octahedral tilting and the decrease of the double exchange between Mn3+ and Mn4+.