The influence of strontium deficiency on thermodynamics of defect formation, structural stability and electrical transport of SrFe0.5Ta0.5O3-δ-based solid solutions with an excess tantalum content.

The crystalline and electronic band structures, thermodynamic stability, oxygen non-stoichiometry and high-temperature transport properties of perovskite-like solid solutions with a general formula Sr1-yFe0.5-xTa0.5+xO3-δ, where x, y ≥ 0, are thoroughly studied using a combination of experimental and theoretical methods. It is argued that the basic compound SrFe0.5Ta0.5O3-δ possesses an orthorhombic lattice symmetry, while its tantalum-doped derivatives belong to a tetragonal space group. Importantly, the purposeful addition of a certain deficiency in a strontium sublattice is shown to be a valid method for stabilizing the Sr1-yFe0.5-xTa0.5+xO3-δ oxides with an excess tantalum content. Detailed studies of charge states in an iron sublattice suggest the predominance of Fe3+ ions even in tantalum-enriched materials. Also, the band structure calculations support the semiconducting nature of electrical transport with localized n-type conductivity provided by small polarons represented by Fe2+ ions. The overall defect structure of Sr1-yFe0.5-xTa0.5+xO3-δ compounds is proved to heavily rely on oxygen vacancy (VO) formation processes; in turn, the presence of strontium vacancies is shown to be an important factor that can decrease the respective energy penalties to introduce VO defects in the lattice. As a result, the experimentally measured oxygen non-stoichiometry for Sr0.95Fe0.45Ta0.55O3-δ at elevated temperatures appears to be sufficiently enlarged as compared to pristine SrFe0.5Ta0.5O3-δ. Similar to that, the conductive properties of tantalum-enriched phase Sr0.95Fe0.45Ta0.55O3-δ are shown to be improved. On the basis of the obtained results, it is argued that cation non-stoichiometry is a valuable tool for enhancing thermodynamic and transport characteristics of perovskite-like compounds, which are currently viewed as promising materials for high-temperature applications.

Modeling the magnetic properties and Mössbauer spectra of multifunctional magnetic materials obtained by insertion of a spin-crossover Fe(III) complex into bimetallic oxalate-based ferromagnets.

In this article, we present a theoretical microscopic approach to describe the magnetic and spectroscopic behavior of multifunctional hybrid materials which demonstrate spin crossover and ferromagnetic ordering. The low-spin to high-spin transition is considered as a cooperative phenomenon that is driven by the interaction of the electronic shells of the Fe ions with the full symmetric deformation of the local surrounding that is extended over the crystal lattice via the acoustic phonon field. The proposed model is applied to the analysis of the series [Fe(III)(sal2-trien)] [Mn(II)Cr(III)(ox)3]·solv, in short 1·solv, where solv = CH2Cl2, CH2Br2, and CHBr3.

Magnetic ionic plastic crystal: choline[FeCl4].

A novel organic ionic plastic crystal (OIPC) based on a quaternary ammonium cation and a tetrachloroferrate anion has been synthesized with the intention of combining the properties of the ionic plastic crystal and the magnetism originating from the iron incorporated in the anion. The thermal analysis of the obtained OIPC showed a solid-solid phase transition below room temperature and a high melting point above 220 °C, indicating their plastic crystalline behaviour over a wide temperature range, as well as thermal stability up to approximately 200 °C. The magnetization measurements show the presence of three-dimensional antiferromagnetic ordering below 4 K. The results from electrochemical characterization display a solid-state ionic conduction sufficiently high and stable (between 10(-2.7) and 10(-3.6) S cm(-1) from 20 to 180 °C) for electrochemical applications.

Isoreticular two-dimensional magnetic coordination polymers prepared through pre-synthetic ligand functionalization.

Chemical functionalization is a powerful approach to tailor the physical and chemical properties of two-dimensional (2D) materials, increase their processability and stability, tune their functionalities and, even, create new 2D materials. This is typically achieved through post-synthetic functionalization by anchoring molecules on the surface of an exfoliated 2D crystal, but it inevitably alters the long-range structural order of the material. Here we present a pre-synthetic approach that allows the isolation of crystalline, robust and magnetic functionalized monolayers of coordination polymers. A series of five isostructural layered magnetic coordination polymers based on Fe(II) centres and different benzimidazole derivatives (bearing a Cl, H, CH3, Br or NH2 side group) were first prepared. On mechanical exfoliation, 2D materials are obtained that retain their long-range structural order and exhibit good mechanical and magnetic properties. This combination, together with the possibility to functionalize their surface at will, makes them good candidates to explore magnetism in the 2D limit and to fabricate mechanical resonators for selective gas sensing.

Unusual 5f magnetism in the U2Fe3Ge ternary Laves phase: a single crystal study.

Magnetic properties of the intermetallic compound U(2)Fe(3)Ge were studied on a single crystal. The compound crystallizes in the hexagonal Mg(2)Cu(3)Si structure, an ordered variant of the MgZn(2) Laves structure (C14). U(2)Fe(3)Ge displays ferromagnetic order below the Curie temperature T(C) = 55 K and presents an exception to the Hill rule, as the nearest inter-uranium distances do not exceed 3.2 Å. Magnetic moments lie in the basal plane of the hexagonal lattice, with the spontaneous magnetic moment M(s) = 1.0 µ(B)/f.u. at T = 2 K. No anisotropy within the basal plane is detected. In contrast to typical U-based intermetallics, U(2)Fe(3)Ge exhibits very low magnetic anisotropy, whose field does not exceed 10 T. The dominance of U in the magnetism of U(2)Fe(3)Ge is suggested by the (57)Fe Mössbauer spectroscopy study, which indicates very low or even zero Fe moments. Electronic structure calculations are in agreement with the observed easy-plane anisotropy but fail to explain the lack of an Fe contribution to the magnetism of U(2)Fe(3)Ge.