Effect of calcination temperature on B-site vacancy content of La0.75Sr0.25Mn0.92Δ0.08O3−δ perovskite

Lanthanum manganite with cation vacancies from nominal La0.75Sr0.25Mn0.92Δ0.08O3−δ nanocrystalline powder was successfully prepared at different calcination temperatures using the sol-gel method. X-ray diffraction shows that as the calcination temperature (TCal) increases, the crystal particle diameter increases, but the B-site vacancy content decreases. According to a powder diffraction profile fitting technique and transmission electron microscopy results, the vacancy content can be estimated as 0.08, 0.01, and 0.005 for TCal = 1073, 1273, and 1473 K, respectively. Magnetization versus temperature curves show that the magnetic transition temperatures, including the Curie temperature, are influenced by both B-site vacancies and double-exchange interaction between Mn3+ and Mn4+ cations. A core-shell model is proposed for vacancies located on the surfaces of the crystal particles. As an application, the magnetic moment angle θij between Mn3+ and Mn4+ cations on the surface, which decreases with decreasing vacancy content, can be obtained.