Liedienov M. Magnetotransport and dielectric properties of nonstoichiometric compositions of bismuth-containing rare-earth manganites with perovskite structure

The thesis is devoted to establishing regularities in the effect of composition and defect structure on the functional properties of rare-earth perovskites. It has been established that a decrease in the temperatures of phase transitions in the course of an isovalent replacement of A-cation by Ln = La3+, Pr3+, Nd3+, Sm3+, Eu3+ ions in rare-earth La0.3Ln0.3Sr0.3Mn1.1O3-δ manganites is caused by an increase in defect structure. The defect molar formulas have been determined for a single-phase Bi1-xLaxFeO3-δ multiferroics obtained by the modified express-method of rapid liquid-phase sintering. It has been found that a sharp increase in the temperatures of phase transitions is observed in the course of a nonisovalent replacement of A-cation by monovalent Ag+ and K+ ions within a limited concentration range of 0 ‒ 20 % for rare-earth manganites with superstoichiometric manganese. It has been shown that an increase in the content of superstoichiometric manganese raises the magnetoresistance and relative dielectric permittivity within UHF range in manganites. It has been established that iron ions B = Fe have the strongest effect on the change of the properties of La0.6Sr0.15Bi0.15Mn1.1-xBxO3-δ manganites, for which the constant of electron-phonon interaction has the highest values. The phase diagrams of magnetic and conductive states for Bi-containing rare-earth manganites have been experimentally constructed.