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.     

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.     

A new phase in stoichiometric Cu6Sn5

The intermetallic compound Cu₆Sn₅ is a significant microstructural feature of many electronic devices where it is present at the solder–substrate interfaces. The time- and temperature-dependent thermomechanical properties of Cu₆Sn₅ are dependent on the nature and stability of its crystal structure, which has been shown to exist in at least four variants (η, η′, η⁶ and η⁸). This research details an additional newly identified monoclinic-based structure in directly alloyed stoichiometric Cu₆Sn₅ using variable-temperature synchrotron X-ray diffraction (XRD) and transmission electron microscopy. The phase is associated with a departure from the equilibrium temperature of the polymorphic monoclinic–hexagonal transformation temperature. The new monoclinic phase can be treated as a modulation of four η⁸-Cu₅Sn₄ unit cells plus one η′-Cu₆Sn₅ unit cell. It has been labeled as η⁴⁺¹ and has cell parameters of a = 92.241 Å, b = 7.311 Å, c = 9.880 Å and β = 118.95° determined from electron diffraction patterns. The XRD results could be fitted well to a Rietveld refinement using the new crystal parameters.     

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.     

Thermoelectric properties of the new tellurides SrSc2Te4 and BaSc2Te4 in comparison to BaY2Te4

The two new ternary scandium tellurides SrSc₂Te₄ and BaSc₂Te₄ were prepared by heating the elements at temperatures between 800 °C and 900 °C under vacuum. Both compounds crystallize in the CaFe₂O₄ type, space group Pnma, Z = 4, with lattice dimensions of a = 13.1795(17) Å, b = 4.2323(7) Å, c = 15.367(2) Å, V = 857.2(2) Å³ for SrSc₂Te₄, and a = 13.292(2) Å, b = 4.2694(7) Å, c = 15.523(3) Å, V = 880.9(2) Å³ for BaSc₂Te₄. The structures comprise a three-dimensional network of edge- and corner-sharing ScTe₆ octahedra. The Sr and Ba cations are located in linear channels, surrounded by eight Te atoms forming bicapped trigonal prisms. SrSc₂Te₄ and BaSc₂Te₄ are electron-precise materials exhibiting common oxidation states, Sr²⁺, Ba²⁺, Sc³⁺, and Te²⁻. We calculated the band gaps to be 0.1 eV for SrSc₂Te₄ and 0.2 eV for BaSc₂Te₄. At room temperature, both materials exhibit a high Seebeck coefficient and low electrical conductivity.     

Ternary intermetallics Hf13.0Ni40.8Ga30.9 and Zr13.0Ni40.6Ga31.0

Ternary compounds Hf_13.0Ni_40.8Ga_30.9 and Zr_13.0Ni_40.6Ga_31.0 were synthesized from the pure elements in arc-melting reactions; their structures were characterized through X-ray diffraction of single crystals. Each compound adopts a hexagonal structure of type Y₁₃Pd₄₀Sn₃₁ and crystallizes in space group P6/mmm (No. 191). The cell parameters of Hf_13.0Ni_40.8Ga_30.9 are a = 17.895(3) Å; c = 8.2434(16) Å; V = 2286.0(6) Å³; R₁/wR₂ = 0.0299/0.0598. The cell parameters of Zr_13.0Ni_40.6Ga_31.0 are a = 17.964(3) Å; c = 8.2757(17) Å; V = 2312.7(7) Å³; R₁/wR₂ = 0.0348/0.0686. These structures comprise polyhedra with diverse coordination numbers – Hf 12–15, Ni and Ga 6–12. Analysis of the structures reveals layer frameworks based on structures of type CaCu₅, accompanied with atomic substitution and elimination on the layers and decreased values of the concentration of valence electrons. Calculated electronic structures reveal a strong contribution from a Ni–Ga interaction and the characteristics of a polar intermetallic phase.     

La5M3X (M=Sn,Bi; X=Cl,Br, I): exploring the limit of the Mn5Si3-type hosting lattice

Three new compounds add to the family of the Mn₅Si₃ type host–guest lattice. These are La₅Sn₃X (X=Cl, Br, I) synthesized from stoichiometric mixtures of La, LaX₃ and Sn heated under Ar atmosphere in sealed Ta ampoules at 850–990 °C for 13–62 days. La₅Sn₃X crystallize in the space group P6₃/mcm (No. 193) with lattice parameters a=9.603(1) Å, 9.637(1) Å and 9.673(1) Å; c=6.890(1) Å, 6.931(1) Å and 6.987(1) Å, respectively, for X=Cl, Br and I. Computational analysis using both the extended Hückel and the local density functional methods showed that the Sn and La site acts as electron reservoir, providing electrons to the interstitials as necessary. This gives rise to a metallic behavior. Susceptibility and conductivity measurements confirmed these predictions. The single crystal structure of La₅Bi₃Br is also reported.     

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).     

Synthesis,characterization and nonlinear optical properties of 2-[(E)-2-(4-ethoxyphenyl)ethenyl]-1-methylquinolinium 4-substitutedbenzenesulfonate compounds

In the present investigation, 2-[(E)-2-(4-ethoxyphenyl)ethenyl]-1-methylquinolinium 4-substituted benzenesulfonate (X = CH₃ (1), X = OCH₃ (2), X = Cl (3), X = Br (4)) have been synthesized and characterized by ¹H NMR, UV–Vis and FT-IR spectroscopy methods. In addition compound 3 was also characterized by single crystal X-ray diffraction (XRD) and found that it crystallized out in the monoclinic space group P2₁ with cell parameters, a = 9.8072(9) Å, b = 6.4848(5) Å, c = 19.4405(16) Å, α = 90°, β = 103.421(5)°, γ = 90°, z = 2 and V = 1202.61(17) Å³. The nonlinear optical absorption of the samples has been studied at 532 nm using 5 ns laser pulses, employing the open-aperture z-scan technique. It is found that some of the samples are potential candidates for optical limiting applications.     

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.     

Crystal and electronic structures and physical properties of two semiconductors: Pb4Sb6Se13 and Pb6Sb6Se17

The title compounds were synthesized by directly reacting the elements in stoichiometric ratios at elevated temperatures. Their crystal structures were determined by single crystal X-ray diffraction. Pb₄Sb₆Se₁₃ crystallizes in the monoclinic space group I2/m with lattice dimensions of a=24.591(1) Å, b=4.0910(2) Å, c=25.212(1) Å, β=93.943(1)°, V=2530.3(2) Å³ (Z=4), while Pb₆Sb₆Se₁₇ crystallizes in the orthorhombic space group P2₁2₁2 with lattice dimensions of a=15.872(4) Å, b=24.061(7) Å, c=4.1382(9) Å, V=1580.4(7) Å³ (Z=2). Electronic structure calculations predicted semiconducting behavior. Temperature dependent electrical conductivity measurements verified this prediction for Pb₄Sb₆Se₁₃.     

Probing structure and microstructure of epitaxial Ni–Mn–Ga films by reciprocal space mapping and pole figure measurements

The crystal structure and complex twinning microstructure of epitaxial Ni–Mn–Ga films on (1 0 0) MgO substrates was studied by X-ray diffraction using 2θ scans, pole figure measurements and reciprocal space mapping (RSM). The orientation distribution of all variants is visualized by RSM, which forms the basis for a better understanding of the crystallographic relation between variants and substrate. Above the martensitic transformation temperature the film consists of single austenite phase with lattice constant a = 5.81 Å at 419 K. At room temperature some epitaxially grown residual austenite with a = 5.79 Å remains at the interface with the substrate, followed by an intermediate layer exhibiting orthorhombic distortion, a_trans = 6.05 Å, b_trans = 5.87 Å, c_trans = 5.73 Å and a major fraction of 14M (7M) martensite, a = 6.16 Å b = 5.79 Å c = 5.48 Å. The seven-layered modulation of this metastable martensite structure is directly observed by RSM. The intermediate phase observed close to interface indicates the existence of an instable, pre-adaptive martensite phase with a short stacking period.     

High-temperature ferromagnetism observed in facing-target reactive sputtered MnxTi1−xO2 films

The crystal structure of reactive sputtered Mn_xTi_1−xO₂ films turns from anatase to rutile as x increases. All the films are ferromagnetic, with a Curie temperature above 340 K. Vacuum annealing enhances the ferromagnetism of the films, but O₂ annealing weakens it, indicating that the ferromagnetism is related to the oxygen-vacancy defects created by Mn⁺² dopants at Ti⁺⁴ cations. The average room-temperature moment per Mn decreases from 0.482 μ_B at x = 0.026 to 0.078 μ_B at x = 0.375. Meanwhile, the optical band gaps value decreases linearly from 3.35 eV at x = 0 to 1.73 eV at x = 0.375, suggesting that Mn ions substitute for Ti ions uniformly and the ferromagnetism is not from magnetic Mn oxide impurities. The high-temperature ferromagnetism makes the Mn_xTi_1−xO₂ films useful for the applications in spintronic devices.     

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 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.     

The crystal structure of high temperature phase Ta2O5

The high temperature phase of Ta₂O₅ and its variants were maintained in a pure Ta₂O₅ specimen using the conventional solid-state reaction method and the advanced laser irradiation technique. The structure of the high temperature phase is determined to be tetragonal with lattice parameters of a = 3.86 Å and c = 36.18 Å and space group of I4₁/amd. Compared to the previously reported crystal structure, the number of the total basis atoms was reduced to be 6 from 11. The modified crystal structure interprets well the recorded high-resolution electron microscopy images and the selected area electron diffraction patterns. Based on the basic tetragonal structure, the crystal lattice structures of the orthorhombic and monoclinic variants were determined and the corresponding space groups were analyzed according to the variation of the symmetrical elements. In addition, crystal atomic structures of these two variants were proposed based on the tetragonal structure.     

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.     

Ta4AlC3: Phase determination,polymorphism and deformation

Ta₄AlC₃, a new member of the M_n+1AX_n-phase family, has been synthesized and characterized (n = 1–3; M = early transition metal; A = A-group element; and X = C and/or N). Phase determination by Rietveld refinement of synchrotron X-ray diffraction data shows that Ta₄AlC₃ belongs to the P6₃/mmc space group with a and c lattice parameters of 3.10884  ± 0.00004 Å and 24.0776 ± 0.0004 Å, respectively. This is shown to be the α-polymorph of Ta₄AlC₃, with the same structure as Ti₄AlN₃. Lattice imaging by high-resolution transmission electron microscopy demonstrates the characteristic MAX-phase stacking of α-Ta₄AlC₃. Three modes of mechanical deformation of α-Ta₄AlC₃ are observed: lattice bending, kinking and delamination.     

Spinodal decomposition in (CaxBa1−x)yFe4Sb12

The thermoelectric and structural properties of a double filled skutterudite solid solution (Ca_xBa_1?x)_yFe₄Sb₁₂ were investigated. Using X-ray powder and X-ray micro analyses (EPMA) an immiscibility gap was established with a critical point at x ≈ 0.45 and a critical temperature that depends on the filling level (T_C = 590 ± 5 °C at y = 0.8 and T_C = 610 ± 5 °C at y = 0.9). The thermoelectric properties were measured for samples prepared in four different states: (i) a single phase solid solution (Ca_xBa_1?x)_yFe₄Sb₁₂; (ii) a two phase microcrystalline mixture of Ca_yFe₄Sb₁₂ and Ba_yFe₄Sb₁₂; (iii) a single phase structure obtained after annealing of the latter sample at 600 °C for 200 h; (iv) a spinodally demixed sample after annealing at 400 °C for 672 h. The thermoelectric properties of the phase mixture (ii) are compatible with data reported for the microcrystalline end members (Ca_yFe₄Sb₁₂ and Ba_yFe₄Sb₁₂), whilst the single phase (i and iii) and spinodally decomposed (iv) samples show increased thermopower and decreased thermal conductivity, similarly to those observed for nano-structured Ca_yFe₄Sb₁₂ and Ba_yFe₄Sb₁₂.     

Composition-dependent crystal structure and martensitic transformation in Heusler Ni–Mn–Sn alloys

In the present work, modulated four- and five-layered orthorhombic, seven-layered monoclinic (4O, 10M and 14M) and unmodulated double tetragonal (L1₀) martensites are characterized in Heusler Ni–Mn–Sn alloys using X-ray diffraction, high-resolution transmission electron microscopy, electron diffraction techniques and thermal analysis. All modulated layered martensites exhibit twins and stacking faults, while the L1₀ martensite shows fewer structural defects. The substitution of Sn with Mn in Ni₅₀Mn_37+xSn_13?x (x = 0, 2, 4) enhances the martensitic transition temperatures, while the transition temperatures decrease with increasing Mn content for constant Sn levels in Ni_50?yMn_37+ySn₁₃ (y = 0, 2, 4). The compositional dependence of the martensitic transition temperatures is mainly attributed to the valence electron concentration (e/a) and the unit-cell volume of the high-temperature phase. With increasing transition temperatures (or e/a), the resultant martensitic crystal structure evolves in a sequence of 4O → 10M → 14M → L1₀ in bulk Ni–Mn–Sn alloys.