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Abstract Materials properties are determined by their compositions and structures. In ABO3 oxides different cation orderings lead to mainly perovskite‐ or corundum like derivatives with exciting physical properties. Sometimes, a material can be stabilized in more than one structural modification, providing a unique opportunity to explore structure‐properties relationship. Here, CoVO3 obtained in both ilmenite‐(CoVO3‐I) and LiNbO3‐type (CoVO3‐II) polymorphs at moderate (8–12 GPa) and high pressures (22 GPa), respectively are presented. Their distinctive cation distributions affect drastically the magnetic properties as CoVO3‐II shows a cluster‐glass behavior while CoVO3‐I hosts a honeycomb zigzag magnetic structure in the cobalt network. First principles calculations show that the influence of vanadium is crucial for CoVO3‐I, although it is previously considered as non‐magnetic in a dimerized spin‐singlet state. Contrarily, CoVO3‐II shows two independent interpenetrating antiferromagnetic Co‐ and ferromagnetic V‐hcp sublattices, which intrinsically frustrate any possible magnetic order. CoVO3‐II is also remarkable as the first oxide crystallizing with the LiNbO3‐type structure where both metals contain free d electrons. CoVO3 polymorphs pinpoint therefore as well to a much broader phase field of high‐pressure A‐site Cobaltites.

Electronic phase separation is an important feature of many correlated perovskite compounds but hasn’t been seen in other complex oxides with similar physical behaviour such as magnetite. Hong et al. find phase separation between a magnetite-like charge ordered phase and a charge averaged phase in CaFe3O5.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Fe2O3 and Fe2O3:Ge nanofibers (NFs) were prepared via electrospinning and thoroughly characterized via several techniques in order to investigate the effects produced by germanium incorporation in the nanostructure and crystalline phase of the oxide. The results indicate that reference Fe2O3 NFs consist of interconnected hematite grains, whereas in Fe2O3:Ge NFs, constituted by finer and elongated nanostructures developing mainly along their axis, an amorphous component coexists with the dominant α-Fe2O3 and γ-Fe2O3 phases. Ge4+ ions, mostly dispersed as dopant impurities, are accommodated in the tetrahedral sites of the maghemite lattice and probably in the defective hematite surface sites. When tested as anode active material for sodium ion batteries, Fe2O3:Ge NFs show good specific capacity (320 mAh g−1 at 50 mA g−1) and excellent rate capability (still delivering 140 mAh g−1 at 2 A g−1). This behavior derives from the synergistic combination of the nanostructured morphology, the electronic transport properties of the complex material, and the pseudo-capacitive nature of the charge storage mechanism.

The original version of this Article contained an error in the third sentence of the legend of Fig. 2, which incorrectly read ‘The phase fractions of the charge ordered (CO) phase, obtained from synchrotron (X) and neutron (N) diffraction data are shown in the right-hand panel.’ The correct version states ‘charge averaged (CA)’ in place of ‘charge ordered (CO)’. This has been corrected in both the PDF and HTML versions of the Article.

Perovskites (ABO3) with mixed transition-metal cations are of particular interest for high-temperature electrochemical and electrocatalytic devices. In this regard, the effects of Sr doping on the structural and electrical properties of the double perovskite La2NiTiO6have been studied. High-resolution neutron powder diffraction (NPD) indicates that the symmetry of the La2−xSrxNiTiO6−δseries changes from monoclinic (space group, P21/n) for low Sr contents, associated with B-site cation ordering, to orthorhombic (Pnma) for x> 0.1 with increasing B-site disorder. The substitution of Sr for La is primarily charge compensated by the creation of oxygen vacancies, as indicated by NPD and analysis of the Ni oxidation state by chemical titration thermal analysis and magnetic measurements. The system exhibits p-type electronic conductivity for oxygen partial pressures (pO2) > 10−18atm, increasing with increasing Sr content (σ= 1.18 S cm−1at 900 °C for x= 0.5 in air). A p–n transition is observed in the range 10−18≤ pO2≤ 10−19atm. Sr-doped materials are less conductive in the n-type regime than the Sr-free parent phase; however, n-type conductivity increases with greater xin the range 0.1–0.5, most probably due to increasing reducibility associated with a higher degree of B-site disorder and defect association. [ABSTRACT FROM AUTHOR]

We provide a full description of the first single-crystal synthesis of the low-dimensional quantum spin compound (CuCl)LaNb2O7through the low-temperature topotactic ion exchange route. Very fast diffusion of ion-exchanged CuCl and Cs ions is observed. In addition, thorough structure determination at very low temperature is outlined following use of single-crystal X-ray diffraction and powder neutron diffraction, taking advantage of the better sensitivity of the latter method for describing O and Cl atoms. State-of-the-art calculations (Maximum Entropy Method) are used for visualising the fine structural features of this unusual pseudo-tetragonal superstructure. Our study unambiguously throws light on the long-standing controversy concerning the crystal structure of this compound, and allows for a relevant description of its magnetic properties. Incidentally, it is demonstrated that the low-temperature structural model tentatively proposed very recently by Tsirlin et al.(Phys. Rev. B, 2010, 82, 054107), according to powder synchrotron X-ray diffraction, is correct. [ABSTRACT FROM AUTHOR]

Cation non-stoichiometry is now recognised to have a significant influence on the electrical-transport properties of proton-conducting oxides. The effects of A-site-cation deficiency in the Sr1−xCe0.9Yb0.1O3−δperovskite system with potential use in electrochemical devices are examined. Electron diffraction is used to verify the orthorhombic perovskite structure (space group, Pnma) of compositions 0 ≤ x≤ 0.06. Combined Rietveld refinements of high-resolution neutron and X-ray diffraction data confirm a previously reported anomalous evolution of the lattice parameters within the series, with a maximum in specific free volume observed for x= 0.04. Analysis of the ion-site occupancies indicates that A-site and oxygen vacancies form up to x= 0.04, with partial partitioning of the Yb dopant over the Sr and Ce sites taking place for higher levels of Sr deficiency. The change in defect chemistry is likely to be responsible for the anomalous evolution in structural parameters, and may arise from the alleviation of strain associated with substantial octahedral tilting which occurs for a high A-site vacancy content. In addition to lattice parameters, electrical transport and stability in CO2are also affected by dopant partitioning. The proton conductivity appears to be well correlated with both the nominal oxygen-vacancy content and the specific free volume. The stability of the series towards carbonation is not correlated to the Sr chemical potential but, instead, is lowest for the composition of greatest specific free volume. [ABSTRACT FROM AUTHOR]

In this paper, we report an extensive neutron diffraction investigation at high temperature on the BaCe 0.80Y 0.20O 2.9proton conducting material. Our results precisely define the structural evolution of this compound as a function of temperature which evolves from the monoclinic structure found at room temperature to the orthorhombic symmetry ( Immaspace group) at 500 °C; then it adopts a rhombohedral structure from 600 to 700 °C and finally transforms into the more symmetric cubic structure at the highest investigated temperature (800 °C). This progressive increase in the symmetry of the system is not accompanied by any first order phase transition as also confirmed by thermal analysis. Finally, combined neutron data and TGA measurement shows that the oxygen content in the sample is stable up to about 700 °C. Above this temperature, the oxygen content reduces from the nominal content of about 2.9 to about 2.8. [ABSTRACT FROM AUTHOR]

The magnetism of the A-site-ordered perovskite LaMm3V4O12 is studied comprehensively by means of neutron powder diffraction experiments and theoretical calculations. Magnetic neutron diffraction results show that a rhombohedral 60° spin structure emerges on the cubic lattice below a 44-K Néel transition. Ab initio electronic structure calculations confirm that high-spin Mn2+ moments are localized while V 3d-band states are itinerant, and that the noncollinear 60° spin structure is more stable than collinear ferromagnetic or G-type antiferromagnetic alternatives. Effective Heisenberg model calculations reveal that the appearance of such a nontrivial spin structure can be attributed to significant next-nearest-neighbor and third-nearest-neighbor magnetic interactions. [ABSTRACT FROM AUTHOR]