The DFT method was used to predict the formation energies and quadrupole coupling constants C-Q in a series of borophosphates: Li3BP2O8, Li2NaBP2O8, Na3BP2O8, Li2B3PO8, Na5B2P3O13, LiNa2B5P2O14 and Na3B6PO13 composed of different networks and different amounts of borate and phosphate units. The change in formation energies with increasing number of B atoms in this series is attributed to the multiplicity of boron sites and is explained by density of states calculations. The calculated C-Q values of Li-7, Na-23 and B-11 are correlated with the coordination and distortion of polyhedra to elucidate the influence of local and more distant environments. As for the C-Q of B-11, it should be in the ranges of 0.26-0.36, 0.48-0.84 and similar to 1 MHz for boron tetrahedral distortion indices of 0.004-0.013, 0.015-0.019 and 0.033, respectively, whereas C-Q similar to 3.0 MHz corresponds to boron in a triangular site. The obtained numerical relationships make it possible to predict the quadrupole frequencies for these nuclei based only on their local environment, and vice versa, to propose structural models from NMR data. These results provide guidance for studying similar characteristics of other borophosphates, the structure of which varies depending on the initial reaction, composition and temperature.

This work studies a series of synthesized Bi1.6Mg0.8-xCuxNb1.6O7-delta (x = 0.2, 0.4) semiconductors and their Li-doped compositions. A detailed structure investigation combining high-resolution neutron-, synchrotron-, and X-ray diffraction methods, as well as DFT calculations, revealed the preferential location of Cu and Li atoms at the Bi sites and Mg atoms at the Nb ones. According to high-temperature X-ray diffraction data, a structural modification caused by the activation of oxygen transport occurs at 200 degrees C. The linear thermal expansion coefficient was found to be 3.6-4.6 center dot 10(-6) K-1 (50-400 degrees C). Magnetic susceptibility measurements allowed us to determine weak antiferromagnetic exchange interactions. The direct band gap was predicted using the DFT-HSE03 hybrid functional calculation, and the optical direct band gap was estimated at 2.3-2.4 eV. Impedance spectroscopy and a dc four-probe technique were also employed to examine the samples' electrical properties. The high mixed electronic-ionic conductivity of the pyrochlores was detected, while the vacancies created by Li-doping in Bi(1.5-y)LiyMg(0.375)Cu(0.375)Nb(1.5)O(7-delta) have been found not to affect the conductivity. Besides, the pyrochlores are chemically compatible with the La0.7Sr0.3MnO3 perovskite (up to 800 degrees C). These make us believe that the studied Mg-Cu-and Mg-Cu-Li-doped bismuth niobate semiconductors can become the basis for composite electrodes to boost their oxygen conductivity.

The nanosized (50-70 nm) pyrochlore Bi1.5Fe0.5Ti2O7-delta was prepared by a coprecipitation technique. Characterization of Bi1.5Fe0.5Ti2O7-delta was carried out by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), Raman spectroscopy, Mossbauer spectroscopy, and magnetic susceptibility measurements. The study of Fe doping in Bi2Ti2O7 was performed by means of density functional theory (DFT) calculations. The nanosized Bi1.5Fe0.5Ti2O7-delta sample crystallizes in the structural type of pyrochlore (Fd (3) over barm). The distribution of Fe atoms over the sites of Bi and Ti was studied from DFT simulations and then confirmed by the XRD analysis and Mossbauer method. The local distribution, electronic structure, and magnetic behavior of nanosized Bi1.5Fe0.5Ti2O7-delta are determined by the local microstructure of the metastable nanosized sample. Based on the examination of the Mossbauer spectrum of the Bi1.5Fe0.5Ti2O7-delta nanopowder, the following states of oxidation were revealed for iron atoms: Fe4+ in the titanium sites with a fraction of similar to 5.7% and two states of Fe3+ (in the Bi and Ti sites) with different geometries of the oxygen surrounding. The ratio of Fe3+ distributed over the sites correlates well with the distribution in the ceramic sample. The presence of Fe4+ was found only in the nanosized Bi1.5Fe0.5Ti2O7-delta. The experimental effective magnetic moment of Fe atoms in the nanosized Bi1.5Fe0.5Ti2O7-delta appeared noticeably lower than that in the ceramic sample. The temperature dependence of mu(eff) within the temperature range of 50-300 K is adequately described by the model of coexistence of Fe3+ and Fe4+ and the existence of clusters.

Using the ultrasonic spray pyrolysis method, a controllable process is realized for self-assembly of spherical BiFeO3 aggregates. Powders are obtained, which exhibit as the pronounced ferromagnetic properties (the coercive force Hc at 8.8 kOe and the residual magnetization Mp at 0.08 emu/g) characteristic of conventionally sol–gel produced BiFeO3 samples (Hc and Mp approaching zero). Various manifestations of ferromagnetism are discussed. It is found that the ultimate values of magnetic characteristics are related to destruction of the antiferromagnetic cycloid as the shells of hollow BiFeO3 spheres are formed. The aggregates thus formed may be considered as an advanced type of bismuth ferrite nanostructure with no coverage in the literature.

Combined ab initio and experimental study of Cr doping into bismuth titanate pyrochlore was carried out for the first time. Accurate first-principles density functional theory calculations were performed considering a Hubbard U correction (DFT+U) to account for on-site Coulomb interactions of the Cr 3d states. The possibility to synthesize a novel pyrochlore-type compound with a high dopant content Bi1.5Cr0.5Ti2O7 (Bi site doping) in a fine powder state was shown via coprecipitation method, while the single-phase Bi2Ti1.5Cr0.5O7 (Ti site doping) could not be obtained. Detailed descriptions of thermostability, structural, optoelectronic, and magnetic properties of Cr-doped pyrochlores in the fine (particles size 100-300 nm) and "bulk" (1-50 μm) powder states are presented based on the well-matched results of theoretical and experimental investigations. According to the Rietveld refinement of the X-ray diffraction data, Bi1.5Cr0.5Ti2O7 compound is an A-site deficient pyrochlore (Bi1.38Cr0.30)(Ti1.84Cr0.16)O6.44 with chromium distribution between both cationic sites. Metastability of fine powder Cr-containing pyrochlore phase was revealed during long-thermal annealing, while the bulk powder sample was stable up to its melting point 1230 °C. According to the study of electronic structure and optical properties, Cr-doped pyrochlores are wide-band semiconductors with light absorption in the range of 300-500 nm and perspective as photocatalytic active materials under visible light irradiation. Paramagnetic behavior with effective magnetic moment 3.92 μB (Bi1.6Cr0.1Ti2O7-δ) and 3.01 μB (Bi1.5Cr0.5Ti2O7) was experimentally observed. All chromium in magnetically diluted pyrochlore Bi1.6Cr0.1Ti2O7-δ exists in the form of Cr3+ monomers, whereas in the more concentrated magnetic Bi1.5Cr0.5Ti2O7 composition Cr3+-O-Cr3+ dimers may also be present, with a fraction equal to 0.39. This investigation constitutes the first approach to the electronic, structural, optical, and magnetic properties of d-elements doped bismuth titanate pyrochlores from experimental and theoretical viewpoints, emphasizing the power of DFT+U to provide insights and to complement the experimental characterization of these new compounds.

A new group of cyclogermanates has been characterized using XRD, DFT calculations, photoluminescence spectroscopy and magnetic study.

The present study focuses on the magnetic properties of the nanotubular Ni3Si2O5(OH)(4) pecoraite, the structural analogue of chrysotile, obtained by hydrothermal synthesis. The cell parameters of the material, determined by X-ray diffraction, are a = 0.528(1) nm, b = 0.917(0) nm, c = 1.460(1) nm and beta = 92.4(7)degrees. The element analysis revealed the decrease of the Ni:Si ratio after hydrothermal treatment. The synthesized nanotubes have bigger outer and inner diameters in comparison to chrysotile. Using a vibration sample magnetometer, we determined the temperature of the ferromagnetic transition (23.7 K), mu(eff) of the Ni2+ ion in pecoraite (3.48 mu B) and the blocking temperature (18 K). Copyright (C) EPLA, 2016

Magnetic properties of the lithium-transition metal orthophosphates LiNiPO4, LiNi0.9Co0.1PO4, LiNi0.9Mn0.1PO4 and LiMnPO4 single crystals have been studied. Temperature behavior of a susceptibility against a type of 3d-transition ion was analyzed. Anomalous behavior is observed over narrow temperature region near Neel point. This is caused by a commensurate-incommensurate magnetic phase transition in pure LiNiPO4, Co- and Mn-doped samples. Using Curie-Weiss model we calculated magnetic constants.

Study of magnetite nanoparticles, as-prepared and dispersed in Copaiba oil as magnetic fluid, by means of magnetic measurement and Mössbauer spectroscopy at various temperatures demonstrated differences in the saturation magnetization and Mössbauer hyperfine parameters which were related to the interactions of Copaiba oil polar molecules with iron cations on magnetite nanoparticle’s surface.

The crystal structure of the promising optical materials Ln2M2+Ge4O12, where Ln=rare-earth element or Y; M=Ca, Mn, Zn and their solid solutions has been studied in detail. The tendency of rare-earth elements to occupy six- or eight-coordinated sites upon iso- and heterovalent substitution has been studied for the Y2−xErxCaGe4O12 (x=0–2), Y2−2xCexCa1+xGe4O12 (x=0–1), Y2Ca1−xMnxGe4O12 (x=0–1) and Y2−xPrxMnGe4O12 (x=0–0.5) solid solutions. A complex heterovalent state of Eu and Mn in Eu2MnGe4O12 has been found.

Compounds with the olivine-type structures are considered as perspective materials for lithium-ion power sources for both industrial and transport applications. Lithium iron phosphate is most highly developed from this family, but LiMnPO4 is supposed as much promising, due to its higher EMF vs. lithium. One of the main lacks of this class of materials is the low electronic conductivity. The traditional ways of conductivity increase by partial replacement of Mn with other transition metal for LiMnPO4 do not result to essential success. Our approach consisting in the influence onto anion sublattice results to better effect. Such solid solutions should be suitable for oxygen nonstoichiometry creation in virtue of ability of vanadium ion for oxidation degree downturn. Using magnetic methods, we succeeded to show that the required solid solutions are really formed. The optimal synthesis conditions of LiMnP1-xVxO4-δ solid solutions were determined. It was shown, that the doping of LiMnPO4 by vanadium jointly with oxygen nonstoichiometry brings to substantial enhance of electronic conductivity in this material. Observed peculiarities of the magnetic properties indicate the restructuring in the local environment in anion sublattice.

AbstractThe title compounds are promising optical materials, in which different lanthanoid elements are introduced as a sensitizer or activator.

Twinning in the adamantine-like quaternary calcogenide Li2ZnSnS4; A crystallographic detective story Charles H Lake, Beth M Leverett, Jonathan W Lekse, Jennifer A Aitken Indiana University of Pennsylvania, Chemistry, Department of Chemistry, Indiana University of Pennsylvania, Indiana, PA 15705, Indiana, PA, 15705, USA, Duquesne University, Department of Chemistry and Biochemistry, 600 Forbes Avenue, Mellon Hall 302, Pittsburgh, PA 15282, E-mail:Lake@iup.edu