Nominal La0 Research Articles

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.

Study of Na substitution in La0.67Ba0.33MnO3 perovskites

The effect of Na substitution on nominal La0.67Ba0.33−x Na x MnO3 (0≤x≤0.33) manganites is studied in this work. Detailed chemical and structural analyses on ceramic samples obtained at 1200 ∘C show that a significantly lower Na rate than the nominal one is obtained due to important Na losses during the synthesis. The losses of Na result in the appearance of impurity phases for high nominal Na rates in addition to the manganite phase with a rhombohedral $R\bar{3}c$ structure. Structural and physical properties of the samples can be properly interpreted according to the variation of the Mn3+/Mn4+ ratio and the average ionic radius of A-site when the experimental composition of the manganite is considered.