ON THE ENERGY TRANSFER IN LiMgPO4 DOPED WITH RARE-EARTH ELEMENTS

The phosphates LiMgPO4: RE (RE - Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm) with olivine-type orthorhombic structure were synthesized by the conventional solid state reaction route and their optical...

A new ternary silicide GdFe1−xSi2 (x=0.32): preparation, crystal and electronic structure

The title compound was prepared from the elements by arc-melting. The crystal structure was investigated by means of single-crystal X-ray diffraction. It crystallizes in the TbFeSi2 structure type, orthorhombic space group Cmmm, a = 4.0496(8), b = 16.416(2), c = 3.9527(6) Å, Z = 4, R1 = 0.041, wR2 = 0.11 for 207 unique reflections with Io > 2 σ(Io) and 19 refined parameters. The Fe position is not fully occupied and the refinement results in a composition GdFe0.68Si2 in agreement with a chemical analysis. The structure consists of zig-zag chains of Si(1) atoms which are terminally bound to additional Si(2) atoms. For an ordered variant GdFe0.5Si2 the Zintl concept can be applied which results in formal oxidation states Gd3+(Fe2+)0.5Si(1)1−Si(2)3−. The electronic structure of this variant GdFe0.5Si2 was analyzed using the tight-binding LMTO method and the results confirm the simple bonding picture.

Crystal structures of the tetrachloridoaluminates(III) of rubidium(I), silver(I), and lead(II)

The reactions of the binary metal chlorides AgCl, RbCl and PbCl2 at T = 180°C in the ionic liquid [BMIm]Cl · 4AlCl3 (BMIm = 1-n-butyl-3-methylimidazolium) yielded air-sensitive, colorless, high-quality crystals of their tetrachloridoaluminate(III) salts. Thereby, the obstructions that hinder proper crystallization of these compounds from pristine AlCl3 melts were circumvented. X-ray diffraction on single-crystals revealed a monoclinic structure (space group P21/c) for Ag[AlCl4], which unexpectedly has a closer relation to Cu[AlCl4]2 than to Cu[AlCl4]. Rb[AlCl4] crystallizes in the baryte structure type (orthorhombic, Pnma), and Pb[AlCl4]2 is isotypic to α-Sr[GaCl4]2 (orthorhombic, Pbca).

Crystal Growth and Physical Properties of Lu(Al1-xTx)B4 (T = Fe, Cr) by Al-Self Flux

Crystals of the quaternary compounds α-Lu(Al1-xTx)B4(T = Fe, Cr) (YCrB4-type, orthorhombic, Pbam), obtained from the nominal composition of Lu(Al1-xTx)B3, were grown by using Al flux mixed with T metal at 1773 K for 5 h under an Ar atmosphere. The maximum dimensions and morphology of the crystals obtained were about 0.7 mm × 0.5 mm for flake-type crystals of Lu(Al1-xCrx)B4and about 5.2 mm × 0.2 mm for prism crystals of Lu(Al1-xFex)B4. The lattice constants determination and chemical analyses of Lu(Al1-xTx)B4(T = Fe, Cr) compounds were carried out for Fe 0.5 - 10.0 at% and Cr 0.5 - 1.0 at%. The lattice constants and the unit lattice volume in Lu(Al1-xTx)B4crystals decreased with increase of the concentration of Fe or Cr. The values of micro-Vickers hardness of Lu(Al1-xFex)B4(x = 0.005 - 0.030) and Lu(Al1-xCrx)B4(x = 0.005 - 0.010) samples are in the ranges of 16(2) - 20(3) GPa and 13(2) - 16(3) GPa, respectively. The hardness values showed a little increase as the solid solution of Fe or Cr was realized in Lu(Al1-xTx)B4, possibly because of distortion to the crystal structure. The magnetic susceptibility of as-grown Lu(Al0.995Fe0.005)B4crystals for example, exhibited diamagnetic behavior with a small ferromagnetic component.

Synthesis and crystal structure of new compounds from the Y–Mg–Ni system

The synthesis, structural characterization, and chemical bonding peculiarities of new intermetallic compounds from Y–Mg–Ni ternary system are reported herein. The crystal structures of these compounds were determined by single-crystal and X-ray powder diffraction analysis. Three ternary compounds were studied: Y2Mg11Ni2 [own structure type, monoclinic, Pearson Symbol mS30, Space Group C2/m, a=18.969(4), b=3.6582(7), c=11.845(2) Å, β=125.07(3)°], Y4Mg3Ni2 [Ru4Al3B2 structure type, tetragonal, P4/mmm, tP18, a=10.8668(2), c=3.59781(12) Å] and YMgNi [MoAlB structure type, orthorhombic, Cmcm, a=3.6713(4), b=17.708(3), c=3.9583(5) Å]. New compositions of Y1−xMgxNi4 and Y5−xMg24+x solid solutions were detected: YMg0.86(1)Ni4.14(1) [SnMgCu4 structure type, cubic, F4̅3m, cF24, a=7.0747(6) Å] and Y4.28(1)Mg24.72(1) [Ti5Re24 structure type, cubic, I4̅3m, cI58, a=11.2655(11) Å]. The crystal structure peculiarities of these compounds are discussed. A particular attention has been given to Y2Mg11Ni2 and its relations with other Mg-containing compounds. Crystallographic analysis together with linear muffin-tin orbital band structure calculations reveals the presence of [Y2Ni4@Mg20] and [Y4Ni2@Mg18] clusters in Y2Mg11Ni2 phase. For Y4Mg3Ni2 the formation of the Ni–Mg nets was observed, while the Y atoms form a monolayer.

Rubidium chalcogenido diferrates(III) containing dimers [Fe2Q6]6− of edge-sharing tetrahedra (Q=O, S, Se)

The two isotypic rubidium chalcogenido diferrates Rb12[Fe2Q6](Q2)3 (Q=S/Se), which both form needles with green-metallic lustre, were synthesized from Rb2S, elemental iron, rubidium and sulfur (Q=S) or from the pure elements (Q=Se) at maximum temperatures of 500–800°C. Their triclinic crystal structures were determined by means of X-ray single crystal data (space group P1̅, a=863.960(10)/903.2(3), b=942.790(10)/982.1(3), c=1182.70(2)/1227.4(4) pm, α=77.4740(10)/77.262(6), β=71.5250(10)/71.462(6), γ=63.7560(10)/63.462(5)°, Z=1, R1=0.0308/0.0658 for Q=S/Se). The structures contain isolated dinuclear anions [FeIII2Q6]6− composed of two edge-sharing [FeQ4] tetrahedra (dFe−Q =223.4–232.3/236.2–244.8 pm), which are also found in the two polymorphs of the pure alkali diferrates Rb6[Fe2Q6]. The diferrate ions are arranged in layers running in the a/b plane around z=0. Inbetween (around $z \approx {1 \over 2}$), two crystallographically different disulfide/diselenide ions $Q_2^{2 - }$ (dQ−Q =211.1–213.4/237.9–241.1 pm), which are arranged in slightly puckered 36 nets, are intercalated. The intra-anionic distances and angles, the Rb coordination numbers and the molar volumes of these two ‘double-salts’ are in accordance with their corresponding reference compounds, Rb6[Fe2Q6] and Rb2Q2. In addition, the two polymorphs of Rb6[Fe2Se6], which are both isotypic with the sulfido analogous (Cs6[Ga2Se6]-type, monoclinic, space group P21/c, a=827.84(5), b=1329.51(7), c=1074.10(6) pm, β=127.130(5)°, R1=0.0443 and Ba6[Al2Sb6]-type, orthorhombic, space group Cmce, a=1963.70(3), b=718.98(3), c=1348.40(7) pm, R1=0.0264) were prepared and characterized to complete the series of alkali diferrates(III) with oxido, sulfido and selenido ligands. The electronic band structures of the three Rb salts Rb6[Fe2Q6], which have been calculated within the GGA+U approach applying an AFM spin ordering in the dimers and appropriate Hubbard parameters, allow a comparison of the chemical bonding characteristics (e.g. covalency) and the magnetic properties (magnetic moments) within the series of chalcogenido ligands. An analysis of the spin densities enables a comparative consideration of the mechanisms crucial for the magnetic ordering in chalcogenido ferrates. Ultimately, the electronic structure of the new compound Rb12[Fe2S6](S2)3 nicely compares with those of the S2-free reference compound Rb6[Fe2S6].