Spontaneous explosive crystallization and phase formation in a nanosized selenide/indium heterostructure

Spontaneous explosive crystallization in a nanosized Se/In heterostructure is experimentally studied. It is demonstrated that spontaneous explosive crystallization in this structure occurs in a wide (70–280 nm) Se thickness range in the narrow time interval of 1.7–3.5 s. It is established that, depending on the Se and In thickness ratio, in reaction product spontaneous explosive crystallization results in the formation of hexagonal InSe with the crystal lattice parameters a = 4.05 Å and c = 16.93 Å and hexagonal Se with a = 4.3662 Å and c = 4.9536 Å.     

Studies of structural transformations and electrical behaviour of FeSe films

The formation of FeSe alloy films as a result of the co-deposition of Se and Fe thin films has been studied. It has been found that the as-grown FeSe film corresponds to a cubic phase with a = 5.37±0.05 Å. The effect of annealing on this FeSe phase has been investigated. At annealing temperatures ranging between 150° and 200°C, the cubic phase transforms to a hexagonal phase (a = 4.00±0.05 Å, c = 5.88±0.05 Å) which resembles one of the known bulk phases of FeSe. On further annealing in the temperature range 250°–300°C, the hexagonal phase transforms to a tetragonal phase with a = 4.18±0.05 Å, c = 4.73±0.05 Å. All the transformations have been found to be irreversible. The electrical behaviour of the FeSe films at various temperatures has also been studied. Evidence for the phase transformations is provided by the nature of the variation of the electrical resistivity with temperature.     

High-pressure,high-temperature study of GeS2 and GeSe2

Phase transitions of the GeX₂ (X = S, Se) dichalcogenides have been studied at pressures of up to p ? 8 GPa and temperatures from 675 to 1375 K, and portions of their p-T phase diagrams have been constructed using our and previous experimental data. The crystal structure of the GeS₂-III phase has been refined by the Rietveld method (HgI₂ structure, P4₂/nmc, a = 3.46906(2) Å, c = 10.9745(1) Å, Z = 2, D _x = 3.438 g/cm³, R = 0.06). GeSe₂-III crystals have been grown for the first time at p ? 7 GPa in the temperature range 875–1275 K. The unit-cell parameters of GeSe₂-III (hex) are a = 6.468 ± 0.004 Å and c = 24.49 ± 0.10 Å (D _meas = 5.16 g/cm³, D _x = 5.18 g/cm³, Z = 12).     

Compounds WAl<Subscript>4</Subscript>, WAl<Subscript>3</Subscript>, W<Subscript>3</Subscript>Al<Subscript>7</Subscript>, and WAl<Subscript>2</Subscript> and Al-W-N combustion products

X-ray diffraction data are presented for combustion products in the Al-W-N system. New, nonequilibrium intermetallic compounds have been identified, their diffraction patterns have been indexed, and their unit-cell parameters have been determined. The phases α-and β-WAl₄ are shown to exist in three isomorphous forms, differing in unit-cell centering. The phases α′-, α″-, and α?-WAl₄ are monoclinic, with a ₀ = 5.272 Å, b ₀ = 17.770 Å, c ₀ = 5.218 Å, β = 100.10°; point groups C12/c1, A12/n1, I12/a1, respectively. The phases β′-, β″-, and β?-WAl₄ are monoclinic, with a ₀ = 5.465 Å, b ₀ = 12.814 Å, c ₀ = 5.428 Å, β = 105.92°; point groups A112/m, B112/m, I112/m, respectively. The compounds WAl₂ and W₃Al₇, identified each in two isomorphous forms, differ in cell metrics (doubling) but possess the same point group: P222. WAl ₂ ^′ : orthorhombic, a ₀ = 5.793 Å, b ₀ = 3.740 Å, c ₀ = 6.852 Å. WAl ₂ ^″ : orthorhombic, a ₀ = 11.586 Å, b ₀ = 3.740 Å, c ₀ = 6.852 Å. W₃Al ₇ ^′ : orthorhombic, Pmm2, a ₀ = 6.225 Å, b ₀ = 4.806 Å, c ₀ = 4.437 Å. W₃Al ₇ ^″ : orthorhombic, Pmm2, a ₀ = 12.500 Å, b ₀ = 4.806 Å, c ₀ = 8.874 Å. The new phase WAl₃: triclinic, P1, a ₀ = 8.642 Å, b ₀ = 10.872 Å, c ₀ = 5.478 Å, α = 104.02°, β = 64.90°, γ = 107.15°.     

Synthesis and properties of structural analogs of the mineral bournonite

Rare-earth analogs of the mineral bournonite, PbCuSbS₃, have been synthesized for the first time and their physicochemical properties have been studied. PbCuSbS₃, EuCuSbS₃, YbCuSbS₃, PbCuLaS₃, and PbCuNdS₃ are isostructural with each other and crystallize in orthorhombic symmetry with the following unit-cell parameters: a = 8.176, b = 8.660, c = 7.796 Å (PbCuSbS₃); a = 8.156, b = 8.68, c = 7.786 Å (EuCuSbS₃); a = 8.15, b = 8.64, c = 7.76 Å (YbCuSbS₃); a = 8.26, b = 8.84, c = 7.96 Å (PbCuLaS₃); a = 8.20, b = 8.80, c = 7.92 Å (PbCuNdS₃) (Z = 4, sp. gr. Pmn2₁).     

Preparation and crystal structure characterization of CuNiGaSe<Subscript>3</Subscript> and CuNiInSe<Subscript>3</Subscript> quaternary compounds

Samples of the quaternary chalcogenide compounds, CuNiGaSe₃ and CuNiInSe₃, prepared by direct fusion and annealing method, were characterized by X-ray powder diffraction. In each case, the crystal structure was refined using the Rietveld method. Both compounds were found to crystallize in the tetragonal system, space group P \(\bar 4\)2c (N°112), with unit cell parameter values a = 5.6213(1) Å, c = 11.0282(3) Å, V = 348.48(1) ų and a = 5.7857(2) Å, c = 11.6287(5) Å, V = 389.26(3) ų for CuNiGaSe₃ and CuNiInSe₃, respectively. These compounds have a normal adamantane structures and are isostructural with CuFeInSe₃.     

Phase relations and crystallization of glass in the system PbO-GeO2

Thermal properties and chemical compositions of glasses suitable for crystallization of ferro-electric Pb₅Ge₃O₁₁ are described. The crystallization of lead germanate glass was investigated by DTA and X-ray diffraction. In the range from 62 to 62.5 of PbO in mole per cent, Pb₅Ge₃O₁₁ was obtained as a single phase after a heat treatment. In the chemical composition around 5PbO·3GeO₂ in the binary system of PbO-GeO₂, Pb₅Ge₃O₁₁ and two new phases of Pb₃Ge₂O₇ and Pb₃GeO₅ were found to exist. The crystal structure of Pb₃Ge₂O₇ had a hexagonal symmetry witha=10.16 Å andc=19.37 Å, and Pb₃GeO₅ was classified into orthorhombic system witha=4.85 Å,b=15.52 Å and c=11.77 Å.     

Hybrid open-frameworks: hydrothermal synthesis,structure determinations and magnetic properties of MIL-29, two copper diphosphonates (CuII(H2O))2{O3P–X–PO3} with X=C2H4, CH2–C6H4–CH2

Two copper diphosphonates were hydrothermally synthesized using ethylenediphosphonic and p-xylenediphosphonic acids, synthesized according the Arbuzov method. The structure of (Cu^II(H₂O))₂{O₃P–CH₂–CH₂–PO₃} already described from powder data, was solved from single crystal data. Its symmetry is monoclinic (space group P2₁/c (no. 14)) with lattice parameters a=8.0670(4) Å, b=7.5889(4) Å, c=7.3997(4) Å, β=116.281(2)°, V=406.18(4) ų, Z=2. The structure of (Cu^II(H₂O))₂{O₃P–CH₂–(C₆H₄)–CH₂–PO₃} was solved by powder X-ray diffraction (space group P2₁/c (no. 14)) with lattice parameters a=10.812(1) Å, b=7.577(1) Å, c=7.412(1) Å, β=92.34(1)°, V=606.7(2) ų, Z=2. Both structures are built up from identical inorganic layers covalently linked by the organic chains which act as pillars. The inorganic layers contain dimers of edge-sharing CuO₄(H₂O) square pyramids linked by the PO₃C tetrahedra. Both compounds are antiferromagnetic at 4(1) K.     

Structure and Superconductivity of the Y4Ba8Cu12O27 Nanosuperconductor

A nanosuperconductor was prepared and characterized in the present work. The nanosuperconductor consisted of nanocrystals with superconducting transition temperature, T _c, of 88 K. Dimension of the nanocrystals is dozens nm in diameter and hundreds nm in length. The compound of the nanocrystals has a formula of Y₄Ba₈Cu₁₂O₂₇. The structure of the nanocrystals was found to be an orthorhombic perovskite, and the lattice constants were determined as a = 7.634 Å, b = 7.758 Å, and c = 11.654 Å, respectively.     

Structure and electrical properties of crystalline and glassy Ag2PbP2O7

Single crystals of Ag₂PbP₂O₇ have been prepared by melting of the crystalline phase under phosphate flux. Ag₂PbP₂O₇, isotype of Na₂PbP₂O₇, is of triclinic symmetry with the space group P(−1) (Z=2). The unit cell parameters are: a=5.502(6) Å, b=7.008(8) Å, c=10.018(9) Å, α=106.63(6)°, β=93.89(7)°, γ=110,68(6)°. The lattice of Ag₂PbP₂O₇ consists of corner-shared structural units {Pb₂P₄O₁₄}⁴⁻, which form ribbons parallel to the [010] direction. The {Pb₂P₄O₁₄}⁴⁻ units result from the association of corner-shared PbO₅ polyhedra and P₂O₇ pyrophosphate groups. The ribbons are interconnected by Pb–O–P bridges in the [100] direction and form lamina parallel to (001) plan. Silver atoms are located between two alternating lamina. Glasses with the same composition as the crystalline phase have been synthesized. A study of transport properties of Ag₂PbP₂O₇ in the crystalline and glassy forms is reported.     

Dehydration/amine intercalation in Zn(O3PR)–H2O phosphonates: the missing link,X-ray structure of Zn(O3PCH3)

The hydrothermal synthesis of colorless crystals of Zn(O₃PCH₃) was achieved using a solution of zinc nitrate and methylphosphonic acid (1:1) in water, in the presence of thiourea. The structure was determined by single crystal X-ray diffraction [monoclinic, space group P2₁/c (No. 14), a=8.7226(9) Å, b=5.2156(7) Å, c=10.847(1) Å, V=389.48(9) ų, Z=2]. From this result, the mechanism of the structure modification taking place during the dehydration of Zn(O₃PR)–H₂O phosphonates was clearly demonstrated.     

Silver(I)–3,6-bis(pyridin-3-yl)-1,2,4,5-tetrazine coordination polymers: a diversity of chain motifs

The influence of solvent and anion on the formation of coordination polymers between silver(I) and 3,6-bis(pyridin-3-yl)-1,2,4,5-tetrazine (3,3′-pytz), a bridging ligand that can adopt both cisoid and transoidconformations, is reported. Reaction of AgPF₆ in MeCN with 3,3′-pytz in CH₂Cl₂ gives ([{Ag(NCMe)₂}(μ-3,3′-pytz)][PF₆]·MeCN)_∞, 1, of AgPF₆ in MeNO₂ and 3,3′-pytz in CH₂Cl₂ gives ([{Ag₂(μ-3,3′-pytz)₂}(μ-3,3′-pytz)][PF₆]₂·4MeNO₂)_∞, 2, and of AgCF₃SO₃ in MeCN and 3,3′-pytz in CH₂Cl₂ gives {[Ag(μ-3,3′-pytz)]CF₃SO₃}_∞, 3. These cationic coordination polymers exclusively form chain structural motifs. That in 1, ([{Ag(NCMe)₂}(μ-3,3′-pytz)]⁺)_∞, has a castellated construction with each tetrahedral silver(I) center coordinated by two solvent molecules as well as two linking transoid-oriented 3,3′-pytz bridges (Ag⋯Ag 13.210 Å) in a 1:1 polymeric chain. That in 2, ([{Ag₂(μ-3,3′-pytz)₂}(μ-3,3′-pytz)]²⁺)_∞, is novel. It is the first coordination polymer to exhibit both cisoid and transoid conformations of a bridging ligand coordinated to the same metal center. Pairs of silver(I) centers are linked by pairs of cisoid-oriented 3,3′-pytz molecules (Ag⋯Ag = 11.695 Å) to form [Ag₂(μ-3,3′-pytz)₂] motifs, which are bridged, in turn, by transoid-oriented 3,3′-pytz molecules (Ag⋯Ag = 13.318 Å) to form a 3:2 ligand:metal infinite polymeric zigzag chain. That in 3, {[Ag(μ-3,3′-pytz)]⁺}_∞, has a zigzag architecture despite being based on linear silver(I) centers. Transoid-oriented 3,3′-pytz molecules link silver(I) centers (Ag⋯Ag 13.225 Å) to give a 1:1 ligand:metal infinite polymeric zigzag chain. The chains aggregate in parallel pairs linked by weak Ag⋯Ag contacts (Ag⋯Ag = 3.220 Å), which are supported by (μ₂-κO,κO′) bridging CF₃SO₃⁻ anions.     

Phase relations and properties of alloys in the SnSe-DySe system

Phase relations in the SnSe-DySe system have been studied using differential thermal analysis, X-ray diffraction, microstructural analysis, microhardness tests, and density measurements, and its T-x phase diagram has been mapped out. The SnSe-DySe system contains a new ternary compound with the composition DySnSe₂, which crystallizes in orthorhombic symmetry with unit-cell parameters a = 5.74 ± 0.02 Å, b = 10.49 ± 0.03 Å, and c = 11.66 ± 0.05 Å (Z = 7, V = 702 ų, measured density ρ_meas = 7.02 g/cm³, X-ray density ρ_x = 7.26 g/cm³). In addition, the system contains SnSe-based solid solutions, Sn_{1 ? x} Dy _x Se (up to 4 mol % DySe). Their electrical conductivity and thermoelectric power have been measured as functions of temperature.     

Hybrid open frameworks: Hydrothermal synthesis and structure determination of MIL-33: a new vanadomethylendiphosphonate intercalating potassium cations

The hydrothermal synthesis and the ab initio structure determination from powder data of K₂(V^VO₂)₄(V^IVO){O₃P–CH₂–PO₃}₂–xH₂O (x=4) or MIL-33 are presented. MIL-33 crystallizes in the monoclinic system [space group C2/m (No. 12)] with lattice parameters a=4.8716(4) Å, b=14.614(1) Å, c=15.825(1) Å, β=94.06(1) Å, V=1123.8(2) ų, Z=2. MIL-33 is a mixed valence V^IV/V^V=1/4 vanadodiphosphonate. Its layered structure shows some potassium cations located both between the hybrid layers and in the eight-membered windows of the latter.     

Atomic structure and enhanced thermostability of a new structure MgYZn4 formed by ordered substitution of Y for Mg in MgZn2 in a Mg-Zn-Y alloy

A new phase MgYZn₄ in Mg-Zn-Y alloy was studied using aberration-corrected scanning-transmission electron microscopy and first-principles calculations. Nanometer-sized MgYZn₄ precipitates were formed through ordered substitutions of Y with 50% Mg atoms in MgZn₂. MgYZn₄ has an orthorhombic structure with a space group of Pmnn, and lattice parameters a =5.2965 Å, b =9.4886 Å, and c =8.5966 Å. Importantly, both size and structure of MgYZn₄ are stable at 625 K for 5 h, showing higher thermostability than MgZn₂, which should be important for applications at elevated temperatures. The enhanced thermostability of MgYZn₄ is attributed to the lower formation energy and bonding enhancement due to Y substitution.     

High-temperature crystal chemistry of Na<Subscript>6</Subscript>(UO<Subscript>2</Subscript>)<Subscript>2</Subscript>O(MoO<Subscript>4</Subscript>)<Subscript>4</Subscript>

Thermal deformations of Na₆(UO₂)₂O(MoO₄)₄ were studied by high-temperature powder X-ray diffraction. The compound crystallizes in the triclinic system, space group Р\(\bar 1\), a = 7.636(7), b = 8.163(6), c = 8.746(4) Å, α = 72.32(9)°, β = 79.36(4)°, γ = 65.79(5)°, V = 472.74(4) ų. It is stable in the temperature interval 20–700°С. The thermal expansion coefficients (TECs) are α₁₁ = 25.5 × 10^–6, α₂₂ = 7.8 × 10^–6, and α₃₃ = 1.1 × 10^–6 (°C)^–1. The orientation of the TEC pattern relative to the crystallographic axes is a₃₃^Z = 45°, a₃₃^X = 122°, a₂₂^Z = 59°, and a₂₂^X = 66°. The anisotropy of the thermal expansion is due to specific features of the crystal structure of the compound.     

Se-TlPrSe<Subscript>3</Subscript> phase diagram

The Se-TlPrSe₃ system has been studied using differential thermal analysis, X-ray diffraction, microstructural analysis, microhardness tests, and density measurements, and its phase diagram has been constructed. The Se-TlPrSe₃ system is shown to be partially nonpseudobinary. The system contains α-TlPrSe₃-based solid solutions with a boundary at 8 mol % Se. The Se solubility in TlPrSe₃ is insignificant. α-TlPrSe₃ has a tetragonal structure with lattice parameters a = 8.87 Å and c = 7.96 Å (ρ_meas = 7.36 g/cm³, and ρ_x = 7.71 g/cm³).     

Hydrothermal synthesis, structure and characterization of new NASICON related potassium iron (III) pyrophosphate

A new potassium iron (III) pyrophosphate was synthesized by hydrothermal technique and characterized by X-ray studies. The compound crystallizes in a monoclinic space group,P2 ₁/c, with cell parameters,a = 7 365(2) Å,b = 10017(2) Å,c = 8.214(1) Å,β = 106.50(1)° andZ = 4. The structure has tunnel-type cavities and are congenial for ion transportation through them. The compound exhibits moderate thermal stability.     

Crystal structures of Ln<Subscript>2</Subscript>TiO<Subscript>5</Subscript> (Ln = Gd,Dy) polymorphs

Single crystals of four Ln₂TiO₅ polymorphs have been grown, and their structures have been determined: orthorhombic (Gd₂TiO₅, a = 10.460(5), b = 11.317(6), c = 3.750(3) Å, Pnam, Z = 4), hexagonal (Gd_1.8Lu_0.2TiO₅, a = 3.663(3), c = 11.98(1) Å, P6₃/mmc, Z = 1.2), cubic (Dy₂TiO₅, a = 10.28(1) Å, Fd3m, Z = 10.4), and monoclinic (Dy₂TiO₅, a = 10.33(1), b = 3.653(5), c = 7.306(6) Å, β = 90.00(7)°, B2/m, Z = 2.4). The last polymorph has been identified for the first time.     

Synthesis and crystal structure determination of Br<Subscript>2</Subscript>SeIBr polyhalogen-chalcogen

In this paper polyhalogen-chalcogen Br₂SeIBr was synthesized and the crystal structure was determined by single crystal X-ray diffraction method. This compound was prepared in the temperature range 150–50°C which was brownish-red in colour and crystallized in monoclinic crystal system and space groupP2_1/c with four molecules per unit cell. Lattice parameters were:a = 6.3711(1),b = 6.7522(2),c = 16.8850(5) Å, α = γ = 90°, β = 95.96°, ν = 722.45 ų.