A quantum-mechanical method for estimating the cation distribution in spinel ferrites is proposed, by which the ionization energy of the cations and the Pauli repulsion energy is considered, together with the magnetic ordered energy and the tendency toward charge density balance. Using this method, not only can the difference between the observed and the traditional theoretical magnetic moments of the spinel structure ferrites MFe2O4 (M=Mn,Fe,Co,Ni,Cu) be explained, but also the dependence of the magnetic moments of the ferrites M1−xZnxFe2O4 (M=Mn,Fe,Co,Ni,Cu) on the doping level x can be fitted.

A quantum-mechanical potential barrier model for estimating the number ratio between different valence cations in multiatom compounds is proposed. It is supposed that there is a potential barrier between a cation-anion pair. The height of the potential barrier is proportional to the ionization energy of the cation, and the width of the potential barrier is related to the distance between neighboring cations and anions. As examples for using this model, the distribution of cations with different valences in some ABO3 lanthanum manganites is explained satisfactorily.

The effects of lanthanum deficiency on the structural and magnetic properties of manganites with normal composition La0.7−xSr0.3MnO3 prepared by the sol-gel method with the highest heat treatment temperature at 800 °C have been investigated. X-ray diffraction (XRD) spectra indicate that the materials possess a single phase with the R3¯c perovskite structure for x≤0.05, and that they possess two phases with the R3¯c perovskite being the dominant phase and Mn3O4 being the second phase for x≥0.10. Using XRD analysis, these materials can be expressed as La0.7−xSr0.3Mn1−yO3−1.5(x+y)/(Mn3O4)y/3. On the basis of the thermal equilibrium theory of crystal defects, the ion ratios at the A, B, and O sites in the ABO3 perovskite phase were calculated. Those ion ratios were used in Rietveld fitting of the XRD spectra. It was found that the dependence of the Curie temperature TC on the content ratio RM4 of Mn4+ ions at B site is similar to that of the typical perovskite La1−xSrxMnO3.

Single-phase perovskite-type manganese oxides La0.8 −xNa0.2□xMnO3+δ with x = 0.01–0.04 have been prepared by the modified sol–gel method and the influence of the vacancy concentration in the A site on their structures and magnetocaloric properties has systematically been investigated. The experimental results revealed that the samples calcinated at 1573 K remained single phase and were constituted by submicrometre homogeneous particles without deviation from the nominal stoichiometry upon heating. For all the compositions explored in this work, the average manganese oxidation state is practically constant, at 3.37 ± 0.02. Magnetic measurement results show that an appropriate amount of vacancy concentration in the A site is favourable to both the Curie temperature and magnetic entropy change for polycrystalline La0.8−xNa0.2□xMnO3+δ compounds. An approximately linear relation between Curie temperature and magnetic entropy change was observed. For La0.771Na0.198Mn1.000□ 0.029O2.94, the largest value of magnetic entropy change of 3.86 J kg−1 K−1 under a field of 10 kOe and the Curie temperature of 364 K were obtained.

A method based on the thermal equilibrium theory of crystal defects for estimating the Mn4+ ion content ratio (RM4) at B sites in ABO3 self-doped manganite La1−xMnO3−δ is presented. For this kind of manganite, the relationship between the Curie temperature (TC) and RM4 can be explained by the double exchange mechanism of Zener, which is similar to that in the perovskite manganite La1−xCaxMnO3.