Expanding frontiers in materials chemistry and physics with multiple anions

During the last century, inorganic oxide compounds laid foundations for materials synthesis, characterization, and technology translation by adding new functions into devices previously dominated by main-group element semiconductor compounds. Today, compounds with multiple anions beyond the single-oxide ion, such as oxyhalides and oxyhydrides, offer a new materials platform from which superior functionality may arise. Here we review the recent progress, status, and future prospects and challenges facing the development and deployment of mixed-anion compounds, focusing mainly on oxide-derived materials. We devote attention to the crucial roles that multiple anions play during synthesis, characterization, and in the physical properties of these materials. We discuss the opportunities enabled by recent advances in synthetic approaches for design of both local and overall structure, state-of-the-art characterization techniques to distinguish unique structural and chemical states, and chemical/physical properties emerging from the synergy of multiple anions for catalysis, energy conversion, and electronic materials

Crystal growth and thermoelectric properties of CaMn0.98Nb0.02O3-delta

Thermoelectric CaMn0.98Nb0.02O3-delta single crystals were grown from sintered polycrystalline material using the traveling-solvent floating zone (TSFZ) method. The floating-zone furnace was operated at over-pressure using an Ar/O-2 mixture to prevent evaporation during the growth process. Six twin-domain variants were detected with single-crystal X-ray diffraction (XRD) and confirmed by electron diffraction (ED) and high-resolution transmission electron microscopy (HRTEM). The Seebeck coefficient (S) of the single-crystalline material indicates n-type semiconducting behavior. Within 10 K < T < 125 K a negative peak in S is observed, known to be characteristic of antiferromagnetic ordering. The ferromagnetic long-range ordering, expected on the basis of double exchange between Mn4+ and doped Mn3+ species, thus appears to remain suppressed in the single-crystalline material. © 2013, Elsevier Ltd

A labile hydride strategy for the synthesis of heavily nitridized BaTiO3

Oxynitrides have been explored extensively in the past decade because of their interesting properties, such as visible-light absorption, photocatalytic activity and high dielectric permittivity. Their synthesis typically requires high-temperature NH3 treatment (800-1,300 °C) of precursors, such as oxides, but the highly reducing conditions and the low mobility of N3- species in the lattice place significant constraints on the composition and structure-and hence the properties-of the resulting oxynitrides. Here we show a topochemical route that enables the preparation of an oxynitride at low temperatures (&lt;500 °C), using a perovskite oxyhydride as a host. The lability of H-in BaTiO3-xHx (x � 0.6) allows H-/N3- exchange to occur, and yields a room-temperature ferroelectric BaTiO3-xN2x/3. This anion exchange is accompanied by a metal-to-insulator crossover via mixed O-H-N intermediates. These findings suggest that this 'labile hydride' strategy can be used to explore various oxynitrides, and perhaps other mixed anionic compounds. © 2015 Macmillan Publishers Limited. All rights reserved