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.     

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).     

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.     

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).     

Composition-dependent electronic properties of indium–zinc–oxide elongated microstructures

Microrods and hierarchical structures of indium–zinc–oxide (IZO) with different compositions were grown by thermal treatments of mixtures of InN and ZnO powders. In long rods, an increase in Zn content along the growth axis is revealed by energy dispersive spectroscopy. The structures obtained range from Zn-doped indium oxide with a few atomic per cent of Zn, to IZO compounds of the type Zn_kIn₂O_k+3. X-ray photoelectron spectroscopy measurements with spatial resolution show that IZO microstructures degenerate at room temperature, with carrier concentration of the order of 10²⁰ cm^?3. Electron accumulation has been found for undoped (1 0 0) and (1 1 1) surfaces, whereas depletion of carriers at the surface is observed in IZO samples. The Fermi level position correlates with the Zn concentration at the surface which, taking into account the surface dependence of the ionization potentials, work functions and band gaps, could lead to tunable material properties for device applications. Cathodoluminescence emission intensity is enhanced by the presence of Zn, which induces spectral changes and broadening of the emission band compared with undoped material. The results are discussed in terms of the charge neutrality level and the band structure of the material.     

Low-temperature specific heat of the superconductor Mo3Sb7

The low-temperature specific heat of a superconductor Mo₃Sb₇ with T_c = 2.2 ± 0.05 K has been measured in magnetic fields up to 5 T. In the normal state, the electronic specific heat coefficient γ_n, and the Debye temperature Θ_D are found to be 34.5(2) mJ mol⁻¹ K⁻² and 283(5) K, respectively. The enhanced γ_n value is interpreted as due to a narrow Mo-4d band pinned at the Fermi level. The electronic specific heat in the superconducting state can be analyzed in terms a phenomenological two BCS-like gap model with the gap widths 2Δ₁/k_BT_c = 4.0 and 2Δ₂/k_BT_c = 2.5, and relative weights of the molar electronic heat coefficients γ₁/γ_n = 0.7 and γ₂/γ_n = 0.3. Some characteristic thermodynamic parameters for the studied superconductor, like the specific heat jump at T_c, ΔC(T_c)/γ_nT_c, the electron–phonon coupling constant, λ_e−ph, the upper H_c2 and thermodynamic critical H_c0 fields, the penetration depth λ, coherence length ξ and the Ginzburg–Landau parameter κ are evaluated. The estimated values of parameters such as 2Δ₀/k_BT_c, ΔC(T_c)/γ_nT_c, N(E_F) and λ_e−ph suggest that Mo₃Sb₇ belongs to an intermediate-coupling regime. The electronic band structure calculations indicate that the density of states near the Fermi level is formed mainly by the Mo-4d orbitals and that there is no overlap between the Mo-4d and Sb-sp orbitals.     

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.     

Oxidation behavior of an Zr53Ni23.5Al23.5 bulk metallic glass at 400–600 °C

The oxidation behavior of the Zr₅₃Ni_23.5Al_23.5 bulk metallic glass (BMG) and its crystalline counterpart was investigated over the temperature range of 400–600 °C in dry air and pure oxygen. In general, the oxidation kinetics of BMG followed the single- or two-stage parabolic rate law at T ≤ 500 °C, with rate constants (K_p values) generally increased with temperature. Conversely, three-stage parabolic kinetics were observed for BMG at T ≥ 550 °C, with K_p values decreased with increasing temperature. The oxidation rate constants for the BMG alloy are slightly higher than those for crystalline alloy at T ≤ 500 °C. In addition, K_p values of BMG were nearly independent of partial pressure of oxygen, implying a typical scaling behavior with a n-type semiconductivity. The scales formed on the BMG is temperature-dependent, consisting mainly of tetragonal-ZrO₂ (t-ZrO₂) and minor amounts of Al₂O₃ at T ≤ 475 °C. At higher temperatures (T ≥ 500 °C), some monoclinic-ZrO₂ (m-ZrO₂) were also detected, and its amounts increased with increasing temperature. The BMG substrate began to form the crystalline Zr₂Ni, Zr₂Al, and ZrNiAl phases beneath the scales after oxidation at T ≥ 450 °C.     

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.     

Stability and elastic properties of L12-(Al,Cu)3(Ti,Zr) phases: Ab initio calculations and experiments

The total energies and equilibrium cohesive properties of L1₂, DO₂₂ and DO₂₃ structures along Al₃Ti–Al₃Zr and Al₃X–Cu₃X (X = Ti, Zr) sections are calculated from first principles employing electronic density-functional theory (DFT), ultrasoft pseudopotentials and the generalized gradient approximation. Calculated heats of formation are consistent with a narrow field of stability of the L1₂ structure at 12.5 at.% Cu for ternary (Al,Cu)_0.75Zr_0.25 and (Al,Cu)_0.75Ti_0.25 intermetallics at low temperatures. Experimentally, samples homogenized at 1000 °C establish a more extensive stability field for the L1₂ phase in quaternary alloys with Cu concentrations ranging from 6.7 to 12.6 at.% Cu. Two L1₂ phases were observed in as-cast alloys with near equal amounts of Ti and Zr, as well as alloys homogenized at 1000 °C. Good agreement is obtained between calculated and measured values of lattice parameters and elastic moduli. These results demonstrate high accuracy of ab initio calculations for phase stability, lattice parameters and elastic constants in multicomponent trialumide intermetallics.     

Structural phase transformation and electrical properties of (0.90 – x)Pb(Mg1/3Nb2/3)O3–xPbTiO3–0.10Pb(Fe1/2Nb1/2)O3 ferroelectric ceramics near the morphotropic phase boundary

Novel solid solutions of (0.90 – x)Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃–0.10Pb(Fe_1/2Nb_1/2)O₃, where x = 0.29, 0.31, 0.33 and 0.35, were investigated from the viewpoint of structural phase transformation, dielectric, ferroelectric and piezoelectric properties. X-ray diffraction and Raman scattering measurements demonstrated that their phase structures experienced a gradual transition process from rhombohedral to tetragonal phase near the morphotropic phase boundary (MPB) region with increasing PbTiO₃ content (x). Corresponding to the structural phase transition near the MPB, large dielectric constants (ε_r) were obtained at the compositions of x = 0.31 (ε_r = 3094 at 1 kHz) and x = 0.33 (ε_r = 2927 at 1 kHz). The maximum remnant polarization (P_r = 26.5 μC cm⁻²) was obtained at the composition x = 0.31, and the electromechanical factor (k_p = 0.59) and piezoelectric coefficient (d₃₃ = 545 pC N⁻¹) were also maximized at this composition, which indicated the enhanced electrical properties near the MPB.     

On new ternary phases from Eu–Zn–T (T = Al and Ga) systems

Novel ternary phases EuZn_2?xGa_2+x, EuZn_2?xAl_2+x, Eu₂Zn_14.32Al_2.68 and Eu₃Zn_17.68Al_4.32 have been synthesized at 400 °C, and characterized by means of X-ray single crystal diffraction at room temperature and magnetic measurements down to 1.72 K. EuZn_2?xAl_2+x and EuZn_2?xGa_2+x compounds crystallize with tetragonal unit cells of the BaAl₄-type. Representatives of these series, namely EuZn_1.25Al_2.75 and EuZnGa₃, order ferromagnetically below 25 K and 14 K, respectively, due to the presence of divalent Eu ions. The other two ternaries studied, i.e. Eu₂Zn_14.32Al_2.68 and Eu₃Zn_17.68Al_4.32, adopt the rhombohedral Th₂Zn₁₇- and the tetragonal Ce₃Zn₂₂-type structure, respectively. Both compounds form with Eu²⁺ ions and possibly order antiferromagnetically at the lowest temperatures investigated.     

Cationic and radical polymerization of N-vinyl-2-phenylpyrrole: Synthesis of electroconducting,paramagnetic and fluorescent oligomers

Cationic polymerization of N-vinyl-2-phenylpyrrole (catalysts: Me₃SiCl, CF₃COOH, BF₃·OEt₂, HCl, WCl₆, FeCl₃, complex LiBF₄–dimethoxyethane, catalysts concentration 1–2 wt%, 20–70 °C, 24–48 h) affords oligomers (molecular weight 1400–1700) of a unexpected structure with alternating 2-phenylpyrrole and ethylydene units, the yields reaching 63%. The oligomers structure has been supported by isolation and identification of the corresponding dimer, N-vinyl-2-phenyl-5-[N-(2-phenyl-1H-pyrrol-1-yl)ethyl]-1H-pyrrole. Radical polymerization of the same monomer (AIBN, 1.5–4 wt%, 60–80 °C, 40–60 h or UV irradiation or both) gives oligomers (molecular weight 2100–3000) of normal structure having polyethene backbone with pendant 2-phenylpyrrole groups in up to 40% yields. The oligomers of both types are semiconductors (1.3 × 10^?6–3.6 × 10^?6 S/cm) after doping with I₂, paramagnetic (4.2 × 10¹⁷–8.7 × 10¹⁷ g^?1) and fluorescent in a near UV region (λ 355–363 nm, acetonitrile).     

Effect of Gd substitution on the crystal structure and multiferroic properties of BiFeO3

The crystal structure, magnetic and local ferroelectric properties of polycrystalline Bi_1?xGd_xFeO₃ (x = 0.1, 0.2, 0.3) samples were investigated at room temperature. Gadolinium substitution was found to induce a polar-to-polar R3c → Pn2₁a structural phase transition at x ≈ 0.1. Increasing the content of the substituting element suppressed the spontaneous polarization in Bi_1?xGd_xFeO₃, resulting in a ferroelectric–paraelectric Pn2₁a → Pnma phase transition at 0.2 < x < 0.3. The substitution caused the appearance of a weak ferromagnetic moment. The data presented are consistent with the hypothesis that the most effective way to induce spontaneous magnetization in antiferromagnetic BiFeO₃ seems to be related to A-site substitution by rare-earth ions with a large difference in ionic radius with respect to Bi³⁺. The effect of the magnetically active Gd³⁺ substitution on the low-temperature magnetic properties of Bi_1?xGd_xFeO₃ samples is also discussed.     

Consideration of the validity of the 14 valence electron rule for semiconducting chimney-ladder phase compounds

Electronic structure calculations for compounds known as Nowotny chimney-ladder (CL) phases have been performed to ascertain an empirical rule that CL compounds with a valence electron concentration (VEC) of 14 are a semiconductors. RuGa₂ and RuAl₂ which have a TiSi₂-type structure, a prototype of the CL phase, with a VEC value of 14 are indirect-gap semiconductors with estimated band gaps of 0.235 and 0.20 eV, respectively. Ru₂Si₃ and Ru₂Ge₃ with VEC=14 are predicted to be direct-gap semiconductors but the band gap decrease in the heavier elements results in closure of the gap in Ru₂Sn₃. Ir₃Ga₅ and Ir₄Ge₅ will be metallic or semimetallic though their VEC values are 14. The Fermi level of Mn₁₁Si₁₉, whose VEC is slightly smaller than 14, is located just before the gap and seems not to be inconsistent with p-type semiconducting behavior. The Fermi levels of Rh₁₀Ga₁₇ and Rh₁₇Ge₂₂ whose VECs exceed 14 are located past the gap. Cr₁₁Gei₁₉ and Mo₁₃Ge₂₃, whose VECs are smaller than 14 would be metallic. These results show that the above rule is a rather good criterion for exploration of semiconducting chimney-ladder phase compounds but compounds with VEC=14 are not always semiconductors.     

Preparation,crystal structures and electrical conducting properties of new charge-transfer salts: (ET)2·SO3CF3 and (ET)·ClO4

Two new charge-transfer (CT) salts: (ET)₂·SO₃CF₃ and (ET)·ClO₄ were prepared by chemical oxidation of ET with AgSO₃CF₃ and AgClO₄, respectively. Their crystal structures were determined: monoclinic system, Cc, a=35.239(7) Å, b=6.5440(13) Å, c=14.646(3) Å, β=110.26(3)°, V=3168.5(11) Å³ for (ET)₂·SO₃CF₃; monoclinic system, C2/c, a=15.981(3) Å, b=10.627(2) Å, c=11.495(2) Å, β=120.61(3)°, V=1680.2(6) Å³ for (ET)·ClO₄. Electrical conductivity measurements indicate that (ET)₂·SO₃CF₃ shows semi-conducting behaviour with room temperature conductivity of 0.29 S cm⁻¹, while (ET)·ClO₄ is an insulator.     

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.     

High-field magnetization and specific heat of UCu2T3Al7 alloys where T = Cr,Mn and Fe(II)

The UCu₂T₃Al₇ alloys, where T = Cr, Mn and Fe, crystallize in the ThMn₁₂-type tetragonal structure. Earlier investigation of magnetic and electrical properties revealed their complex magnetic behavior except of the Cr compound, which is paramagnetic, whereas their electrical resistivity is weakly temperature dependent. At present we report on the magnetization measurements at 4.2 and 77 K in the steady magnetic field up to 14 T and in the pulsed field up to 34 T with a pulse duration of 10 ms at T = 4.2 K. These experiments confirmed paramagnetism of the Cr alloy and showed lack of saturation for the compounds of the Mn and Fe with the “saturation” magnetic moment amounting to 3.1 and 5.0 μ_B/f.u., respectively. In turn, the specific heat was measured in the temperature range 1.2–70 K in magnetic field μ₀H = 0 and 7 K using a home-made and fully automatic calorimeter. The investigation of the specific heat at temperature 2–300 K has been done using Quantum Design PPMS machine. The magnetic field does not in principle influence the obtained results, whereas the coefficient of the electronic specific heat, γ is strongly enhanced and amounts to 410, 330 and 150 mJ mol^?1 K^?2 for the Cr, Mn and Fe compounds, respectively.     

Square net distortion engineering in the ternary variants of titanium antimonide,Ti2−δMδSb (M = Zr,Hf)

The binary antimonide Ti₂Sb crystallizes in a unique structure type, which may be considered as a distorted variant of the La₂Sb structure type. The new ternary variants, Ti_2−δM_δSb (M = Zr, Hf) with δ < 0.85, were prepared by arc melting the elements in stoichiometric ratios. The ternaries crystallize in the body centered tetragonal space group I4/mmm, with lattice dimensions varying with δ and M, e.g. a = 3.977(1) Å and c = 15.011(2) Å for Ti_1.5Zr_0.5Sb (Z = 4). Single crystal structure investigations as well as powder X-ray profile refinements employing the Rietveld method and pair distribution function technique revealed, that with increasing δ the distortions lessen and finally disappear, as was predicted based on the Kleinke–Harbrecht structure map.