A composition-dependent ``re-entrant'' crystallographic phase transition in the substitutional metal acetylacetonate complex (Cr1-xGax)(acac)(3)

The formation of a complete solid solution between acetylacetonate (acac) complexes of chromium and gallium, (Cr1-x,Ga-x)(acac)(3) for 0.1 <x <0.9, has been investigated through the co-synthesis method. Wellcrystallised, subliming solids are found to form for each nominal value of x, with thermal analysis confirming each composition to have a congruent melting point, making it a substitutional complex. Whereas the pure complexes (i.e. the end members of the solid solution, x = 0 and x = 1) are both centro-symmetric, a composition-dependent crystallographic phase transition to a non-centrosymmetric structure is found to occur for compositions with 0.4 < x < 0.9. Such a ``re-entrant'' crystallographic transition is interpreted to be due to the drive to overcome the disorder present in certain centrosymmetric chromium-rich compositions, by going over to a non-centrosymmetric structure with a doubling of the unit cell. The substitutional complex is shown to lead to a substitutional oxide with the beta-gallate structure. (C) 2014 Elsevier Ltd. All rights reserved

Distinct Phase Formation of BiREWO6 (RE = La-Yb) Nanoparticles by a One Step Hydrothermal Synthesis and Their Photocatalytic Applications

Under identical hydrothermal condition, remarkably, Aurivillius BiREWO6 nanoparticles crystallize in an orthorhombic phase for RE = Ce and La, while the RE = Nd-Yb materials crystallize in the monoclinic phase. This kind of distinct phase formation in this series is not observed in solid state synthesis, where for all RE substitution, only the monoclinic phase is formed. Moreover, formation of the orthorhombic phase for BiLaWO6 and BiCeWO6 has been observed for the first time. Calcination of as-synthesized BiLaWO6 and BiCeWO6 nanomaterials results in the monoclinic phase and this indicates that the formation of the orthorhombic phase is favored only under mild reaction conditions. This could be attributed to the crucial role of the ionic radii of RP3+ and Be3+ ions in solution. Rietveld refinement confirms the BiCeWO6 and BiGdWO6 are isostrutural to the low temperature (LT) orthorhombic phase and mondinic high temperature (HT) phase of Bi2WO6, respectively. Additionally phase dependent distinct morphology and photocatalytic activity is observed. As a representative example, it is observed that needle/plate-shaped monoclinic BiGdWO6 nanoparticles show superior visible light driven photocatalytic activity for the Congo-red dye degradation over the spherically agglomerated orthorhombic BiCeWO6 nanomaterial

High Surface Area SnO2-Ta2O5 Composite for Visible Light-driven Photocatalytic Degradation of an Organic Dye

SnO2-Ta2O5 nanocomposite was synthesized by a facile coprecipitation method and further calcined to obtain crystalline powder. Phase formation, morphology, bandgap and photocatalytic properties were analyzed using powder X-ray diffraction, scanning electron microscopy, UV-Vis diffused reflectance spectroscopy, BET surface area and Raman spectroscopy, respectively. Effect of calcination temperature on the crystallinity of the composite was studied. The as-prepared samples of SnO2, Ta2O5 and SnO2-10wt%Ta2O5 composite as well as the calcined composite sample were tested for photocatalytic activity for methylene blue dye degradation under visible light. Photocatalytic studies reveal that the as-prepared SnO2-10wt%Ta2O5 composite showed the best photocatalytic activity for the degradation of methylene blue (MB) by harvesting visible-light radiation efficiently. Further mineralization of methylene blue, estimated by COD analysis, is found to have degraded with an efficiency of 91.6%. The study demonstrates that heterostructure of SnO2-Ta2O5 nanocomposite could be applied in photocatalytic purification of organic pollutants

Photoluminescence tuning of Na_1−xK_xNdW₂O₈ (0.0 &#8804; x &#8804; 0.7) nanoparticles: synthesis, crystal structure and Raman study

A series of Na_1−xK_xNdW₂O₈ (0.0 &#8804; x &#8804; 0.7) nanoparticles have been synthesized by an efficient glycothermal technique for the first time. SEM measurements confirmed the particle size ranges from 30–200 nm with ellipsoidal shaped morphology. Combined X-ray and neutron diffraction and Raman spectroscopy techniques were utilized in order to investigate the influence of K⁺ ion substitution in NaNdW₂O₈. K⁺ ion substitution in the crystal lattice introduced a change in the Nd–O bond length and the Nd–O–W bond angle of NaNdW₂O₈. The photoluminescence intensity increased up to the threshold composition x = 0.4. K⁺ ion substitution resulted in blue shifted emission of NaNdW₂O₈. Size mismatch, the Nd–O–W angle and local disorder contributed to the observed difference in luminescence properties. Also, the chromaticity diagram for this blue emitting phosphor showed the possibility of tuning the emission by incorporation of K

An amine functionalized zirconium metal-organic framework as an effective chemiresistive sensor for acidic gases

Pore surface functionalization of a metal-organic framework (MOF) with an amine moiety has turned an innocent MOF into a chemiresistive sensor for acidic gases. The Zr-NH2-benzenedicarboxylate MOF (NH2-UiO-66) proved to perform as an efficient and stable chemiresistive sensor for SO2, NO2 and CO2 at low concentrations and an operating temperature of 150 degrees C

Effect of Solvent on the Red Luminescence of Novel Lanthanide NaEu(WO₄)₂ Nanophosphor for Theranostic Applications

Investigation of the red luminescence in NaEu­(WO₄)₂ nanoparticles synthesized using water and ethylene glycol and its biocompatibility on HeLa cells, <i>Escherichia coli</i>, <i>Staphylococcus aureus</i>, and <i>Candida albicans</i> has been evaluated for the first time. The Scheelite-like pure tetragonal NaEu­(WO₄)₂ nanoparticles have been synthesized by a simple solvothermal method by using water (NaEuW I) and ethylene glycol (NaEuW II) as a reaction medium. Detailed particle size and crystal structural analysis of both samples were carried out using high resolution transmission electron microscopy and Synchrotron powder diffraction. Enhanced red fluorescence was observed on increase in calcination temperature in both samples, signifying their greater stability and increased crystallinity on thermal treatment. The blue shift of charge transfer (CT) band in NaEuW II nanoparticles is explained by the nature of the Eu–O bond lengths obtained by Rietveld refinement using Synchrotron diffraction data. Chromaticity diagrams revealed the possibility of tuning the red emission of as-prepared and annealed samples against particle size, choice of solvent, and calcination temperature. The calculated Commission Internationale de l’Eclairage (CIE) coordinates of NaEuW II at 600 °C matches the CIE values of the commercial red phosphor Y₂O₃S:Eu³⁺ standards of the National Standards of Television Commission (NSTC). This indicates the potential applications of nano-NaEuW [NaEu­(WO₄)₂] to generate red emission. Investigation of solvent effect on particle size dependent biocompatibility of NaEu­(WO₄)₂ via <i>in vitro</i> cytotoxicity studies showed no significant toxicity toward HeLa cells, <i>E. coli</i>, <i>S. aureus</i>, and <i>C. albicans.</i> More interestingly, bioimaging studies show excellent biodistribution and localization of luminescent nano-NaEuW II. Hence, our preliminary studies could demonstrate a new strategy to design nanoluminescent NaEu­(WO₄)₂ for theranostic applications

In Situ Neutron Diffraction Studies of LiCe(WO4)(2) Polymorphs: Phase Transition and Structure-Property Correlation

Polymorphs of LiCe(WO4)(2) alpha-LiCe(WO4)(2) and beta-LiCe(WO4)(2)] were successfully synthesized by a citric acid-assisted sol-gel method for the first time. Phase purity and crystallinity were confirmed by powder X-ray diffraction and further characterized by X-ray photoelectron spectroscopy, field emission scanning electron microscopy, Raman, and thermogravimetric-differential thermal analysis measurements. Investigation of the effect of calcination temperature and time indicated the existence of an irreversible structural phase transition from low-temperature (LT) beta-phase to high-temperature (HT) alpha-phase, which is systematically followed by in situ HT powder neutron diffraction (NPD) studies. Rietveld refinements using NPD data revealed that alpha-LiCe(WO4)(2) crystallizes in tetragonal Scheelite-type structure (I4(1)/a), while beta-LiCe(WO4)(2) crystallizes in triclinic alpha-LiPr-(WO4)(2)-type structure (P (1) over bar). Furthermore, beta-LiCe(WO4)(2) undergoes a reconstructive phase transition where WO6 of the beta-phase rearranges to WO4 at HT in alpha-phase and is supported by Raman measurements. Anodic redox activities of these polymorphs were determined by cyclic voltammetry and galvanostatic charge-discharge measurements. Interestingly, beta-phase has shown promising results compared with that of alpha-phase, which is attributed to the easy Li-ion diffusion in between the parallel layers of WO6 and also to the greater structural stability of the beta-phase. Thus, our initial understanding on the structure-property of these LiCe(WO4)(2) polymorphs provides insights into the design of new insertion anode electrodes for Li-ion batteries

Polymorphism in photoluminescent KNdW₂O₈: synthesis, neutron diffraction and Raman study

Polymorphs of KNdW2O8 (&#945;-KNdW2O8 and &#946;-KNdW2O8) phosphors were synthesized by an efficient solution combustion technique for the first time. The crystal structure of the polymorphs analyzed from Rietveld refinement of neutron diffraction data confirms that &#945;-KNdW2O8 crystallizes in the tetragonal system (space groupI4̅), and &#946;-KNdW2O8 crystallizes in the monoclinic system (space group C2/m). The local structure of both polymorphs was elucidated using combined neutron Pair Distribution Function (PDF) and Raman scattering techniques. Photoluminescence measurements of the polymorphs showed broadened emission line width and increased intensity for &#946;-KNdW2O8 in the visible region compared to &#945;-KNdW2O8. This phenomenon is attributed to the increased distortion in the coordination environment of the luminescing Nd3+ ion. Combined PDF, Rietveld and Raman measurements reveal distortions of the WO6 octahedra and NdO8 polyhedra in &#946;-KNdW2O8. This crystal structure–photoluminescence study suggests that this class of tungstates can be exploited for visible light emitting devices by tuning the crystal symmetr

Na2.44Mn1.79(SO4)(3): a new member of the alluaudite family of insertion compounds for sodium ion batteries

Sodium-ion batteries have been extensively pursued as economic alternatives to lithium-ion batteries. Investigating the polyanion chemistry, alluaudite structured Na2Fe2II(SO4)(3) has been recently discovered as a 3.8 V positive electrode material (Barpanda et al., Nature Commun., 5: 4358, 2014). Registering the highest ever Fe-III/Fe-II redox potential (vs. Na/Na+) and formidable energy density, it has opened up a new polyanion family for sodium batteries. Exploring the alluaudite family, here we report isotypical Na2+2xMn2-xII(SO4)(3) (x = 0.22) as a novel high-voltage cathode material for the first time. Following low-temperature (ca. 350 degrees C) solid-state synthesis, the structure of this new alluaudite compound has been solved adopting a monoclinic framework (s.g. C2/c) showing antiferromagnetic ordering at 3.4 K. Synergising experimental and ab initio DFT investigation, Na2+2xMn2-xII(SO4)(3) has been found to be a potential high-voltage (ca. 4.4 V) cathode material for sodium batteries

Investigation of Ca substitution on the gas sensing potential of LaFeO₃ nanoparticles towards low concentration SO₂ gas

The present work investigates the superior ability of LaFeO3 (LaFeO) and La0.8Ca0.2FeO2.95 (LaCaFeO) nanoparticles to detect 3 ppm SO2 gas. The influence of calcium substitution on the sensing behaviour of LaFeO has been studied. High resolution TEM images show that the particle sizes of LaFeO and LaCaFeO are less than 100 nm and SEM images show the agglomeration of interconnected nanoparticles. Both LaFeO and LaCaFeO crystallize in the orthorhombic crystal system with the space group Pbnm. Rietveld analysis of neutron diffraction data showed that LaCaFeO has lattice oxygen vacancies. In addition, magnetic refinements on both the samples have been carried out. The presence of lattice oxygen vacancies in LaCaFeO is qualitatively supported by Raman and XPS measurements. Electrical characterization showed increased conductivity for the LaCaFeO sample, influencing their sensing performance significantly. The LaCaFeO nanoparticles exhibit higher sensitivity, faster response time, rapid recovery time and good recyclability for sensing 3 ppm SO2 gas. This enhanced sensing behavior is attributed to the increased oxygen vacancies in the lattice as well as the surface. As a consequence, increased active sites are created in LaCaFeO, promoting redox reaction between the analyte and the sensing material. The results demonstrated that while LaFeO is a good gas sensor, p-type substitution by Ca2+ renders this material an improved resistivity based gas sensor to detect low concentration SO2