Search results for " Crystal"

2009

Abstract. In-situ ice crystal size distribution measurements are presented within the tropical troposphere and lower stratosphere. The measurements were performed using a combination of a Forward Scattering Spectrometer Probe (FSSP-100) and a Cloud Imaging Probe (CIP), which were installed on the Russian high altitude research aircraft M55 "Geophysica" during the SCOUT-O3 campaign in Darwin, Australia. One of the objectives of the campaign was to characterise the Hector convective system, which appears on an almost daily basis during the pre-monsoon season over the Tiwi Islands, north of Darwin. In total 90 encounters with ice clouds, between 10 and 19 km altitude were selected from the dat…

Exploring the self-assembly of resorcinarenes : from molecular level interactions to mesoscopic structures

2012

A new tool for evaluating and/or selecting analytical methods: Summarizing the information in a hexagon

2019

Abstract A quantitative evaluation tool is proposed, which aims to assess optimal selection or/and testing of analytical methods. Objective criteria related to analytical performance, sustainability, environmental impact and economic cost are evaluated through the definition of penalty points divided into five different blocks, namely, figures of merit, toxicity and safety, residues, carbon footprint and economic cost. For each block, the overall qualification is scaled from 0 to 4 and it is depicted on a regular hexagonal pictogram that allows a user friendly comparison of analytical procedures. The present evaluation tool aims to be a guideline for evaluating and/or selecting analytical p…

X-ray powder diffraction study of the stability of solid solutions in LaO(Cl1−xBrx)

1997

Abstract The formation of solid solutions in the LaO(Cl 1− x Br x ) series was studied by X-ray powder diffraction (XPD), Rietveld profile refinement and bond valence calculations. The LaO(Cl 1− x Br x ) (0 ≤ x ≤ 1, step 0.2, and x = 0.5) powder samples were prepared by the solid state reaction between La 2 O 3 and a mixture of ammonium chloride and bromide. The X-ray powder diffraction patterns were collected at room temperature between 5 and 125° in 2Θ using Cu K α 1 radiation (λ = 1.5406 A). The XPD data between 20 and 90° were analyzed with the DBWS-9006PC Rietveld profile refinement program. All the LaO(Cl 1− x Br x ) phases studied crystallize in the tetragonal PbFCl-type structure wi…

Structure and Properties of YbZnSn, YbAgSn, and Yb2Pt2Pb

1999

Abstract YbZnSn, YbAgSn, and Yb2Pt2Pb were synthesized by reacting the elements in sealed tantalum tubes in a high-frequency furnace. The structures of YbAgSn and Yb2Pt2Pb were refined from single crystal X-ray data: YbAgPb type, P 6 m2, a=479.2(2) pm, c=1087.3(3) pm, wR2=0.050, BASF=0.34(8), 509 F2 values, 18 variables for YbAgSn and Er2Au2Sn type, a=776.0(1) pm, c=701.8(2) pm, wR2=0.072, 426 F2 values, 18 variables for Yb2Pt2Pb. The lattice constants of YbZnSn are confirmed: NdPtSb type, P63mc, a=464.7(1) pm, c=747.7(2) pm. The stannides YbZnSn and YbAgSn crystallize with superstructures of the AlB2 type. The zinc (silver) and tin atoms form ordered Zn3Sn3 and Ag3Sn3 hexagons, respectivel…

Syntheses, structures and physical characterization of two new three-dimensional mixed-valence hexadecavanadate derivatives

2007

Abstract Two new hexadecavanadate derivatives, (bpy)[Zn(4,4′-bpy)2]2[H4ClV16O38]·6H2O 1 and (bpy)[Co(4,4′-bpy)2]2[H4ClV16O38]·6H2O 2 (bpy = 4,4′-bipyridine), were synthesized under the hydrothermal conditions and structurally characterized by IR, XPS and EPR spectroscopy, redox titration and single-crystal X-ray diffraction. The two compounds are isostructural and crystallize in the tetragonal non-centrosymmetric space group P-4n2 (No. 118) with a = 17.124(2), b = 17.124(2), c = 14.724(3) A, V = 4317.5(12) A3 and Z = 1 for the compound 1, and a = 17.038(2), b = 17.038(2), c = 14.754(3) A, V = 4282.9(12) A3 and Z = 1 for the compound 2. Compounds 1 and 2 were constructed from 4-connected {H4…

Characterization of the non-stoichiometry in lanthanum oxyfluoride by FT-IR absorption, Raman scattering, X-ray powder diffraction and thermal analys…

1997

Abstract The FT-IR absorption, FT-Raman scattering, X-ray powder diffraction (XPD), and thermogravimetry were used to explore the non-stoichiometry in LaOF. The TGA-DTA analyses between 30 and 1500°C showed that the LaO1 − xF1 + 2x phases yielded the stoichiometric LaOF as an intermediate product. The temperature of formation of the LaOF and La2O3 increased with increasing excess of fluoride. The room temperature XPD data in 6.5 ⩽ 2θ ⩽ 121° range were analyzed by the Rietveld profile refinement method and subsequently by the bond valence calculations. All LaO1 − xF1 + 2x phases possess the tetragonal PbFCl-type structure (space group: P4/nmm; Z = 2) while the stoichiometric LaOF has the hex…

Structural and magnetic properties of the solid solution series Sr2Fe1–xMxReO6(M = Cr, Zn)

2005

Strong correlations between the electronic, structural and magnetic properties have been found during the study of doped double perovskites Sr2Fe1−xMxReO6 (0 ≤ x ≤ 1, M = Zn, Cr). The interplay between the van Hove singularity and the Fermi level plays a crucial role for the magnetic properties. Cr doping of the parent compound Sr2FeReO6 leads to a non-monotonic behaviour of the saturation magnetization and an enhancement for doping levels up to 10%. The Curie temperatures monotonically increase from 401 to 616 K. In contrast, Zn doping leads to a continuous decrease in the saturation magnetization and the Curie temperatures. Superimposed on the electronic effects is the structural influenc…

New alkoxo-bridged mixed-valence cobalt clusters: Synthesis, crystal structures and magnetic properties

2008

Two new Co II /Co III complexes, [{Co II Co III (mea) 3 } 2 (bpe) 3 ](ClO 4 ) 4  · 1.5CH 3 OH · 1.5H 2 O ( 1 ) and [ Co 4 II Co 3 III ( dea ) 6 ( CH 3 COO ) 3 ] ( ClO 4 ) 0.75 ( CH 3 COO ) 1.25 · 0.5 H 2 O ( 2 ) [Hmea = monoethanolamine H 2 dea = diethanolamine and bpe = 1,2-bis(4-pyridyl)ethane], have been obtained by reacting cobalt(II) perchlorate ( 1 and 2 ), Hmea ( 1 )/H 2 dea ( 2 ), bpe ( 1 ) and sodium acetate ( 2 ). The crystal structures of 1 and 2 have been solved by single crystal X-ray diffraction. Crystal 1 contains “Chinese lantern”-like shaped cations, resulting by connecting two {Co II Co III (mea) 3 } moieties with three flexible bpe ligands. The coordination sphere of the …

Stability of Rare-Earth Oxychloride Phases: Bond Valence Study

2002

Abstract The crystal structures of the tetragonal rare earth ( RE ) oxychlorides, RE OCl ( RE =La–Nd, Sm–Ho, and Y) were studied by X-ray powder diffraction measurements, Rietveld analyses, and bond valence calculations. The tetragonal structure (space group P 4/ nmm , No. 129, Z =2) is stable for all but Er–Lu oxychlorides, which possess a hexagonal structure. The tetragonal structure consists of alternating layers of ( RE O) n n + complex cations and X n − anions, where the rare earth is coordinated to four oxygens and four plus one chlorines in a monocapped tetragonal antiprism arrangement. The Rietveld analyses yielded a coherent series of structural parameters. Preferred orientation an…