Pashchenko, A.V., Liedienov, N.A., Li, Quanjun, Tatarchuk, D.D., Turchenko, V.A., Makoed, I.I., Sycheva, V.Ya., Voznyak, A.V., Kladko, V.P., Gudimenko, A.I., Didenko, Y.V., Kozakov, A.T., and Levchenko, G.G.
• Real molar formulas for BiFeO 3−δ and Bi 0.9 La 0.1 FeO 3−δ multiferroics were determined. • Real structure contains Bi3+, La3+, Fe2+, Fe3+, O2− ions and V(a), V(c) vacancies. • Dielectric constant ε ′ reduces in 5000 times at 1 Hz with rising P from 200 to 400 MPa. • Bi 0.9 La 0.1 FeO 3−δ multiferroics show a large value of H C ≥ 10 kOe at room temperature. • "Composition, Structure, Non-stoichiometry, Properties" correlation was established. The structure, microstructure, valence states, non-stoichiometry, dielectric and magnetic properties of lanthanum-modified multiferroics have been studied by X-ray diffraction, thermogravimetric, iodometric titration, SEM, XPS, dielectric spectroscopy and magnetic methods. Multiferroics of bismuth ferrite have been obtained by a rapid liquid phase sintering method under different pressures, P , for compacting stoichiometric mixture of precursors. On the basis of the experimental data, the molar formulas of real BiFeO 3−δ and Bi 0.9 La 0.1 FeO 3−δ structures have been determined. The real structure contains Bi3+, La3+, Fe3+, Fe2+ and O2− ions as well as cation V(c) and anion V(a) vacancies. The optimal temperature regimes of the rapid liquid phase sintering method for obtaining the single-phase Bi 0.9 La 0.1 FeO 3−δ , whose composition corresponds to the concentration region of destruction of a spin cycloid, have been defined. It has been established that oxygen non-stoichiometry δ and concentration of Fe2+ strongly depend on the pressure P. The initial dielectric permittivity of the Bi 0.9 La 0.1 FeO 3−δ multiferroics can be controlled and changed by the pressure P more than 5000 times. The correlations between the composition, structure, non-stoichiometry, dielectric and magnetic properties in the BiFeO 3−δ and Bi 0.9 La 0.1 FeO 3−δ have been established. In the pure BiFeO 3−δ at room temperature, rhombohedral distortions of a hexagonal structure with indications of a ferromagnetic double exchange have been detected. The magnetic structure of the single-phase Bi 0.9 La 0.1 FeO 3−δ is homogeneous with a large value of coercivity, H C ≥ 10 kOe, at room temperature. An analysis of the magnetic properties indicates the appearance of a weak ferromagnetism due to the destruction of the spin cycloid by lanthanum ions. [ABSTRACT FROM AUTHOR]