Nano-domain states of strontium ferrites SrFe1−yMyO2.5+x (M=V, Mo; y≤0.1; x≤0.2)

•Two major nanodomain states were found for SrFe1−yMyO2.5+x (M=V, Mo, y<0.1; x<0.2).•Both contain vacancy-ordered orthorhombic domains intergrown with cubic matrix.•First (y≤0.03) shows orthorhombic and second (0.04≤y≤0.08) – cubic XRD patterns.•First contains 1D twinned lamellar domains with low-angle boundaries and deformations.•Second contains intergrown isotropic in 3D domains perpendicular oriented in matrix.

Series of the oxygen-deficient strontium ferrites SrFe1−yMyO2.5+x (M=V, Mo, y<0.1; x<0.2) substituted with high-charged cations have been investigated by HRTEM and synchrotron radiation XRD. For artificial lowering of x, all the compounds were treated and quenched in vacuum from 950 °C, which led to the formation of the vacancy-ordered brownmillerite phase at local order. Depending on y, the substituted strontium ferrites have three differently disordered nano-domain states. At y≤0.03 there are twinned lamellar 1D nano-domain structures. At 0.04≤y≤0.05 and 0.06≤y≤0.08 the intergrown 3D nano-domain structures with two different types of disorder are formed. The higher the y, the lower the domain size. Disordering phenomena of the 3D nano-domain states were examined with local structure simulations followed by the Debye calculation of XRD patterns.

Graphical abstractEvolution of nano-domain structure with an increase in the substitution degree y in strontium ferrites SrFe1−yMyO2.5+x (M=V, Mo; y≤0.1; x≤0.2): an increase in y decreases the average size of domains and increases the degree of disorder, thus producing the lamellar (1D) or 3D nano-domains.Figure optionsDownload full-size imageDownload as PowerPoint slide