Crystal structure of [NBu4]2[Pd2{C4(COOMe)4}2(μ-OH)2] determined ab initio by charge flipping

The crystal structure of bis(tetra-n-butylammonium)bis(μ₂-hydroxo)-bis(1,2,3,4-tetrakis(methoxycarbonyl)-1,3-butadiene-1,4-diyl)-di-palladium, [NBu₄]₂[Pd₂{C₄(COOMe)₄}₂ (μ-OH)₂], was determined ab initio by X-ray single-crystal diffractometry using the charge flipping method. The compound crystallizes in the monoclinic system with P2₁/c as space group and the following cell parameters: a = 12.8481(6) Å, b = 63.744(3) Å, c = 16.6102(8) Å, β = 111.943(10). The asymmetric unit is formed by two molecules, and the unit cell contains eight molecules (Z = 8) giving a density of 1.369 g cm^?3. The coordination around the Pd(II) atoms is approximately planar, the methoxycarbonyl groups at the α and β positions relative to Pd are perpendicular and parallel to the palladacycle ring, respectively, and the {Pd(μ-O)}₂ core has a bent conformation. The structure closely resembles the features reported previously for other palladacyclopentadiene complexes.     

Crystal structure and X-ray diffraction pattern of CuSnTi3 intermetallic phase

A new ternary compounds of Cu, Sn, and Ti, CuSnTi₃, was found in this study, by isothermally treating Cu–23 at.%Ti–17 at.%Sn alloy at 900 °C for 10 h. This new ternary intermetallic compound has a hexagonal structure with a=0.4636 nm and c=0.5229 nm. Its crystal is of the same structure as that of Ni₃Sn₂, both of which have a space group of P6₃/mmc (hP6, No.194). In such a crystal structure, Cu and Sn are both arranged in the lattice positions of 2c (x=1/3, y=2/3, z=1/4, occ.=0.5), and Ti is arranged in 2a (x=0, y=0, z=0, occ.=1) and 2d (x=1/3, y=2/3, z=3/4, occ.=0.5).     

Synthesis,crystal structure and thermal behavior of Na4[B10O16(OH)2]·4H2O

New hydrated sodium borate Na₄[B₁₀O₁₆(OH)₂]·4H₂O has been synthesized under mild hydrothermal conditions at 170 °C. The structure was determined by single-crystal X-ray diffraction and further characterized by FT-IR, Raman spectra and DTA-TG. It crystallizes in the monoclinic space group Pc with a unit cell of dimension a = 11.323(2) Å, b = 6.5621(14) Å, c = 12.244(3) Å, α = 90°, β = 91.050(3)°, γ = 90°, V = 909.7(3) Å³, Z = 2. The crystal structure of Na₄[B₁₀O₁₆(OH)₂]·4H₂O consists of Na–O polyhedra and [B₁₀O₁₆(OH)₂]⁴⁻ polyborate anions. Dehydration of this compound occurs in three steps and leads to an amorphous phase which undergoes crystallization.     

Crystal structure and properties of the new ternary compound Mg21Ga5Hg3

The crystal structure of a new ternary compound Mg₂₁Ga₅Hg₃ has been studied using X-ray powder diffraction data by Rietveld method. Scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDXS) was used for sample composition examination. The compound crystallizes in the Ge₈Pd₂₁ structure type (space group I4₁/a, a = 1.45391(5) nm, c = 1.15955(4) nm, Z = 4). All interatomic distances indicate metallic type bonding. The average thermal expansion coefficients α_a, α_c and α_V of Mg₂₁Ga₅Hg₃ are 2.60 × 10^?5 K^?1, 2.02 × 10^?5 K^?1, and 7.25 × 10^?5 K^?1, respectively. Electrical resistivity of Mg₂₁Ga₅Hg₃ was measured between 5 and 300 K.     

Laves phases in the ternary systems Ti–{Pd,Pt}–Al

Formation and crystal structure of Laves phases in the systems Ti–{Pd,Pt}–Al were investigated employing XPD (X-ray powder diffraction), XSCD (X-ray single crystal diffraction) and EPMA (electron probe microanalysis) techniques. Laves phases with MgZn₂ type (space group: P6₃/mmc) and its variant with the Nb(Ir,Al)₂-type (a√3 × a√3 × c supercell of MgZn₂-type, space group: P6₃/mcm) were found in both systems. Formation of a particular structure type is dependent on temperature and composition. Laves phases with the Nb(Ir,Al)₂-type form around 25 at.% of Pd,Pt at 950 °C. The MgZn₂-type Laves phase Ti(Pt,Al)₂ was not observed at 950 °C, but it forms in as-cast alloys at a slightly lower Pt content, Ti_37.8Pt_19.0Al_43.2. In the Ti–Pd–Al system at 950 °C the MgZn₂-type phase exists at the Pd-poor side of the homogeneity region whilst the Nb(Ir,Al)₂-type phase is slightly richer in Pd. Phase relations associated with the Ti–Pt–Al Laves phase were established at 950 °C and reveal a new compound TiPtAl that derives from hexagonal ZrBeSi-type (ordered Ni₂In-type, a = 0.43925(4) nm, c = 0.54844(5); space group P6₃/mmc; R_F2 = 0.015 from single crystal data). Atom distribution in the compound shows a slight deviation from full atom order Ti(Pt_0.97Al_0.03)(Al_0.98Pt_0.02).     

The structure and magnetic properties of Th4Mn13Sn5

We have synthesized the new intermetallic compound Th₄Mn₁₃Sn₅: it crystallizes with the Th₄Fe₁₃Sn₅ type structure, tetragonal tP44, space group P4/mbm, a = 8.423(1) Å and c = 11.972(2) Å. The Mn ions in Th₄Mn₁₃Sn₅ order ferro/ferrimagnetically around 110 K. A low magnetization of 0.13 μ_B/Mn at 4.2 K in a field of 70 kOe and a large fractional temperature independent contribution to susceptibility in the paramagnetic regime suggest an appreciable itinerancy of the Mn 3-d state in this compound. The electrical resistivity shows an anomaly at the magnetic transition and varies as T² below 30 K with a coefficient of 8.38 × 10^?3 μΩ cm/K². The low temperature heat capacity data furnish a Sommerfeld coefficient of 16.9 mJ/g atom K². In the course of present work we have also identified the ThMn_0.2Sn₂ phase which adopts a defective CeNiSi₂ type structure, orthorhombic oS16, space group Cmcm with a = 4.476(2) Å, b = 17.059(3) Å and c = 4.398(1) Å.     

Electronic properties and crystal structures of RE3Rh2Ga2 and RE3Rh3Si2 (RE = La,Ce)

Polycrystalline samples of Ce₃Rh₂Ga₂, Ce₃Rh₃Si₂ and their La-based isostructural analogues were studied by means of magnetic susceptibility, magnetization and electrical resistivity measurements. The crystal structure of La₃Rh₃Si₂ (Ce₃Rh₃Si₂ type) was investigated by single-crystal X-ray diffraction. The cerium gallide was found to order ferromagnetically at T_C = 3.5 K, whereas for the silicide more complex magnetic behaviour was established with antiferromagnetic order setting at T_N = 6.5 K and subsequent change in the magnetic structure occurring at T_t = 5.5 K. Both cerium compounds exhibit weak Kondo effect. The L_III-edge XAS data indicated rather stable 4f¹ character of cerium in both compounds. The electronic band structures of Ce₃Rh₂Ga₂ and Ce₃Rh₃Si₂ were calculated by the LMTO method and compared with those of Ce₃Rh₂Ge₂ and La₃Rh₂Ge₂. For each Ce-based compound the total electronic DOS is dominated by a peak of Ce 4f states near the Fermi level and a Rh 4d band located about 2 eV below the Fermi energy.     

Spin-glass-like behaviour in the ternary U3Fe4+xAl12−x uranium–iron aluminide

The U₃Fe_4+xAl_12?x (0 < x < 0.5) intermetallic was prepared by arc melting, followed by annealing at 850 °C. This compound crystallizes in the hexagonal Gd₃Ru₄Al₁₂-type structure (e.g. P6₃/mmc), with room temperature parameters a = 8.7516(3) Å and c = 9.2653(4) Å for x = 0. The structure is characterized by planar layers of M3Al4 (M = Gd, U), containing M atoms in a triangular arrangement and forming a distorted Kagomé net. Magnetic measurements revealed a spin-glass-type behaviour with a freezing temperature, T_f = 7.9 K. The magnitude of the frequency shift of the freezing temperature is ≈0.03 and a Vogel–Fulcher law is followed with values typical for a spin-glass. ⁵⁷Fe Mössbauer data show that there is no freezing of the iron magnetic moments directions below T_f, indicating that the origin of the spin-glass-like behaviour is related to topological frustration of the uranium moments.     

Intermetallic compounds in the M–Cu–Sn systems with M = Eu,Sr, Ba

Several samples were prepared in the title systems, starting from the elements sealed under argon in Ta crucibles, melting in an induction fornace and annealing at 823 K. Six ternary phases were found: EuCu₂Sn₂, a = 11.100 (3), b = 4.307 (1), c = 4.824 (1) Å, β = 108.88 (1)°, and SrCu₂Sn₂, a = 11.197 (4), b = 4.322 (2), c = 4.859 (1) Å, β = 108.43 (1)°, C2/m, CaCu₂Sn₂-type, closely related to the BaAl₄ structure; Sr₃Cu₈Sn₄, a = 9.3280 (2), c = 7.8826 (4) Å, P6₃mc, Nd₃Co₈Sn₄-type, ordered variant of the BaLi₄-type; SrCu₄Sn₂, a = 8.176 (1), c = 7.799 (1) Å, I4/mcm, CaNi₄Sn₂-type; SrCu₉Sn₄, a = 8.663 (1), c = 12.457 (2) Å, and BaCu₉Sn₄, a = 8.717 (1), c = 12.545 (2) Å, I4/mcm, LaFe₉Si₄-type, ordered variant of the NaZn₁₃ structure. The structure of the first compound was refined by the Rietveld method, while single crystal data were used for the others. Some remarks are given on the crystal chemistry of the encountered and related structure types.     

Crystal structure of τ5–TiNi2−xAl5 (x = 0.48) and isotypic {Zr,Hf}Ni2−xAl5−y

The crystal structure of the compound in the Al-rich region of the Ti–Ni–Al system, τ₅–TiNi_2?xAl₅, x = 0.48, has been derived from X-ray powder and single crystal, neutron powder and electron diffraction (space group I4/mmm, a = 0.3984(2) nm, c = 1.4073(3) nm, R_F2 = 0.0133). Titanium atoms were unambiguously located from neutron powder data. τ₅ is isotypic with the crystal structure of ZrNi₂Al₅. Detailed transmission electron microscopy (TEM) in several crystallographic directions confirmed the lattice parameters and crystal symmetry. Although occupancy of Ni in the 4e site revealed a defect (occ. = 0.76), no significant homogeneity region was observed for this phase at 1020°C. Rietveld analyses of X-ray powder diffraction data for the Zr- and Hf-homologues confirmed for both compounds isotypism and revealed defects in the Ni sites and to a lesser extent also in the Al sites: ZrNi_2?xAl_5?y, x = 0.4, y = 0.4 and HfNi_2?xAl_5?y, x = 0.5, y = 0.2. The crystallographic relations among the structure types of Cu, TiAl₃, ZrNi₂Al₅ and Zr(Ni,Ga)₇ have been defined in terms of a Bärnighausen scheme.     

Structure of a new ternary compound with high magnesium content,so-called Gd13Ni9Mg78

The magnesium-rich composition Gd₁₃Ni₉Mg₇₈ was synthesized from its constituent elements in sealed tantalum tubes in an induction furnace. X-ray diffraction, electron probe microanalysis and dark-field transmission electron microscopy (TEM) images revealed a new compound with a composition ranging from Gd_10–15Ni_8–12Mg_72–78 and low crystallinity. In order to increase the crystallinity, different experimental conditions were investigated for numerous compounds with the initial composition Gd₁₃Ni₉Mg₇₈. In addition, several heat treatments (from 573 to 823 K) and cooling rates (from room temperature quenched down to 2 K h^?1) have been tested. The best crystallinity was obtained for the slower cooling rates ranging from 2 to 6 K h^?1. From the more crystallized compounds, the structure was partially deduced using TEM and an average cubic structure with lattice parameter a = 4.55 Å could be assumed. A modulation along both a¹ and b¹ axis with vectors of modulation q1 = 0.42a¹ and q2 = 0.42b¹ was observed. This compound, so-called Gd₁₃Ni₉Mg₇₈, absorbs around 3 wt.% of hydrogen at 603 K, 30 bars and a reasonable degree of reversibility is possible, because after the first hydrogenation, irreversible decomposition into MgH₂, GdH₂ and NiMg₂H₄ has been shown. The pathway of the reaction is described herein. The powder mixture after decomposition shows an interesting kinetics for magnesium without ball milling.     

Isothermal section at 950 °C of the U–Fe–B ternary system

A systematic investigation of the isothermal section at 950 °C of the U–Fe–B ternary system was done by means of X-ray powder diffraction, scanning electron microscopy, complemented by energy dispersive X-ray spectroscopy, and electron-probe microanalysis. At this temperature the phase diagram is characterized by the formation of four ternary compounds with negligible homogeneity regions. The compounds are: UFeB₄ (orthorhombic YCrB₄-type structure, a = 5.887(1) Å, b = 11.412(2) Å and c = 3.4355(4) Å), UFe₃B₂ (hexagonal CeCo₃B₂-type structure, a = 5.049(1) Å and c = 2.9996(7) Å), ∼UFe₄B (structure closely related with the CeCo₄B-type, and a small hexagonal cell a = 4.932(1) Å and c = 7.037(2) Å), and U₂Fe₂₁B₆ (Cr₂₃C₆-type structure, a = 10.766(4) Å).     

Crystal structure and properties of U2Co3Al9

A new ternary compound with stoichiometry U₂Co₃Al₉ has been synthesized. It adopts the orthorhombic Y₂Co₃Ga₉-type structure (space group Cmcm, Z = 4, a = 12.824(2) Å, b = 7.515(1) Å, c = 9.249(2) Å). Measurements of dc- and ac-magnetic susceptibility, electrical resistivity, and magnetoresistivity on polycrystalline samples have been performed. The Curie–Weiss law is strictly followed, with θ_CW = −48 K and μ_eff = 3.2 μ_B. A small kink observed in the temperature dependence of the resistivity is attributed to a phase transition at T_t = 8 K. The magnetoresistivity was found to be negative at all temperatures examined below 45 K, with a sharp minimum at T_t = 8 K.     

Ternary phases in the Yb–Zn–Al system with La3Al11- and Yb8Cu17Al49-type structures

Several compounds with La₃Al₁₁- and Yb₈Cu₁₇Al₄₉-type structures were synthesized in the ternary Yb–Zn–Al system and their crystal structure and existence range were determined by both single-crystal and powder methods. For two of them, crystallizing with the La₃Al₁₁-type, orthorhombic, Immm, o/28, refinement was made by single-crystal data: Yb₃Zn_6.16Al_4.84, a = 428.95(4) pm, b = 975.5(1) pm, c = 1257.3(2) pm, wR2 = 0.052; Yb₃Zn_4.84Al_6.16, a = 427.03(5) pm, b = 988.6(1) pm, c = 1249.5(2) pm, wR2 = 0.104. Though zinc and aluminium share the same sites, some preferential occupation is recognizable. This phase forms between 35 and 50 at% Al. On the Zn-rich side, starting from binary Yb₃Zn₁₁, a replacement of ∼3 at% Al for Zn is reached, then a heterogeneity range appears. Two other phases, crystallizing with the Yb₈Cu₁₇Al₄₉-type, tetragonal, I4/mmm, tI74, were determined by single-crystal methods: Yb₈Zn_48.5Al_17.5, a = 874.6(2) pm, c = 1615.8(3) pm, wR2 = 0.055; Yb₈Zn_41.4Al_24.6, a = 869.5(3) pm, c = 1637.1(7) pm, wR2 = 0.104. The structure of these latter compounds can be related to the Th₆Mn₂₃ type. A common building unit is found and several coordination polyhedra show similar features. Two atomic sites with zinc only and four with Zn/Al mixtures are filled.     

The z value dependence of photoluminescence in Eu2+-doped β-SiAlON (Si6−zAlzOzN8−z) with 1 ≤ z ≤ 4

Eu²⁺-doped β-SiAlON (Si_6?zAl_zO_zN_8?z) phosphors with 1 ≤ z ≤ 4 were synthesized by gas pressure sintering. The emission spectra exhibit two broad bands with maxima at about 415 nm (violet) and 540 nm (green) under ultraviolet excitation. The green emission is dominant at z ≤ 2, while the violet emission becomes dominant at z > 2. The combination of two emission bands in a compound could lead to a white emission in Eu²⁺-doped β-SiAlON with 2 < z ≤ 3.     

Crystal structure of the new ternary germanide Tb4Zn5Ge6

The Tb₄Zn₅Ge₆ phase was prepared by arc melting in an argon atmosphere and then annealed at 670 K for 400 h. The structure of orthorhombic Tb₄Zn₅Ge₆ was determined by single-crystal X-ray diffraction (Cmc2₁, Z = 4, a = 4.2330(10) Å, b = 18.576(4) Å, c = 15.275(3) Å, R₁ = 0.0272 and wR₂ = 0.1076). The structure is isostructural to Gd₄Zn₅Ge₆ and composed of edge- and corner-sharing ZnGe₄ tetrahedra, Tb-atoms forms trigonal prisms filled by Ge-atom.     

Experimental investigation on the phase equilibria of the Mn–Ni–Zn system at 400 °C

Partial isothermal section of the Mn–Ni–Zn system at 400 °C was experimentally established by means of XRD and SEM/EDS techniques. Three ternary compounds, i.e. T, τ₁ and τ₂, were found to exist at 400 °C for the first time. The compound T having an approximate formula of Mn₇Ni₇Zn₈₆ was indexed as fcc structure with a lattice parameter of a = 1.81476 (1) nm. τ₁, the structure of which is unknown, has an approximately stoichiometric composition of about 29 at.% Mn, 38 at.% Ni and balanced Zn. τ₂ has fcc structure and a composition range of about 46–40 at.% Mn and constant 30 at.% Zn. Extended single-phase regions of the phases Mn₅Zn₂₁, Ni₂Zn₁₁, NiZn₃, NiZn and β-Mn were observed. The maximum solubility of Ni in Mn₅Zn₂₁ and those of Mn in Ni₂Zn₁₁, NiZn₃ and NiZn were determined to be 10, 6, 26 and 25 at.% at 400 °C, respectively.     

Neutron structural and vibrational studies of dipotassium selenate tellurate

At room temperature the potassium selenate tellurate K₂SeO₄·Te(OH)₆ (KSeTe) was prepared from water solution of H₆TeO₆ and K₂SeO₄. Its structure has been determined from single crystal using neutron diffraction data. KSeTe is monoclinic with C2/c space group. The unit cell parameters are: a = 11.572(9) Å, b = 6.437(7) Å, c = 13.938(1) Å, β = 106.07(7)°, V = 997.7(1) Å³ and Z = 4. The main feature of this structure is the presence of two different and independent anions (TeO₆⁶⁻ and SeO₄²⁻) in the same unit cell. The structure is built by layers of TeO₆ octahedra altering with planes of SeO₄ tetrahedra linked by a network of hydrogen bonds performed by protons belonging to the OH hydroxide groups. DSC measurements indicate that the crystals of K₂SeO₄·Te(OH)₆ undergo three endothermal peaks at 433, 480 and 495 K.Raman scattering measurements on KSeTe material taken between 300 and 620 K are reported in this paper. The spectra indicate clearly these phase transitions.     

Growth and luminescence characteristics of cerium-doped yttrium pyrosilicate single crystal

Yttrium pyrosilicate (Y₂Si₂O₇, YPS) is an incongruent compound and has five (or possibly six) different structural forms from 1535 to 1225 °C. It should be very difficult to grow YPS single crystal through traditional pulling method. In this paper, cerium doped yttrium pyrosilicate (Y₂Si₂O₇:Ce) single crystals were successfully grown by Floating Zone (Fz) method through composition adjustment and relative rapid growth speed and cooling rate. The crystal structure was confirmed to be orthorhombic with space group Pna2₁ and density of 4.04 g/cm³. Typical Ce³⁺ luminescence was observed by photoluminescence spectrum measurement. Some optical properties of YPS:Ce, such as transmittance and decay time, were measured and compared with that of Lu₂Si₂O₇:Ce crystal. Under 342 nm excitation and 360 nm emission, the decay time of YPS:Ce crystal was 30 ns. This is the fastest value in the cerium doped silicate scintillators up to the present. Its potential application prospect as scintillation material will be also evaluated in this paper.     

Synthesis of 2-phenylquinoline-based ambipolar molecules containing multiple 1,3,4-oxadiazole spacer groups

A series of donor–acceptor type ambipolar electroluminescence dyes with the general structure PQ(OXD)_nT (where n = 1, 2 and 3) were prepared, in which PQ is 2-phenylquinoline, T is diphenylamine which constituted the hole transporting triphenylamine moiety with an adjacent phenyl ring, and OXD is an electron transporting 2-phenyl-1,3,4-oxadiazole repeating unit. The compounds fluoresced bluish green to green hue in solid-state, exhibited a positive solvatochromism in solution and their quantum efficiency decreased rapidly with increase in n. The materials are thermally stable with glass transition temperature (T_g) ranging from 83 °C (n = 1) to 130 °C (n = 3). Cyclic voltammetry studies indicated the HOMO remained relatively unchanged with n while the LUMO decreased (away from the vacuum level) with an increase in the number of OXD. For single layer homojunction OLEDs, highest efficiency was obtained when n = 1 (max luminous 3300 cd/m² and current efficiency 0.9 cd/A), whereas for multilayer heterojunction OLEDs, best results was achieved for compounds with n = 1 or 2 assuming the role of the HT layer (over 8200 cd/m² max and 2.0 cd/A). Formation of exciplexes led to significant red-shift and lower emission efficiency for the compound with n = 3.