Four distinct classes of multiferroics are usually being discussed in the literature, in which ferroelectricity is respectively driven by electronic lone pairs, geometry, charge ordering, and magnetism. Each class has its own shortcomings for technological applications. Here, through a combined experimental and theoretical investigation, we propose a mechanism to achieve multiferroicity in a single phase by engineering the anionic network and creating local geometric distortions in fluorinated, vacancy-ordered brownmillerite Ca 2 Mn 2 O 5−x F y . The system exhibits both ferroelectricity and an antiferromagnetic order above room temperature, pointing toward a novel route to multiferroicity by anion mixing.

Preferred orientation in polycrystalline materials is one of the most challenging problems for structural analysis. Significant preferred orientation can severely affect the structure-property analysis of the systems having substantial crystallographic anisotropy. Here, an extremely high degree of preferred orientation has been demonstrated in R-block hollandite hexagonal PbFe x V 6−x O 11 compounds, which has recently been shown to exhibit an unusual colossal electroresistance response that has a strong dependence on structural modifications. The present results warn against possible errors in understanding the evolution of the crystal structure of these hollandites, which might adversely affect the estimation of the influence of the same on their spectacular physical properties.