Explosive crystallization in the course of formation of Se/Ag nanosize film structure

Results of an experimental study of explosive crystallization appearing in the process of formation of a Se/Ag nanosize film structure are presented. It is shown that explosive crystallization appears in a wide range of Se film thicknesses (70–280 nm) and occurs during a narrow time interval (2.00–4.52 s). The cooperative effect of the thermal energy of the phase transformation of Ag₂Se and the energy of elastic stress in the amorphous Se film leads to development of an explosive crystallization. It was found that, depending on the relative thicknesses of Se and Ag films, orthorhombic Ag₂Se with crystal-lattice constants a = 4.333 Å, b = 7.062 Å, and c = 7.764 Å and hexagonal Se (a = 4.3552 Å and c = 4.9495 Å) are formed in the reaction products upon the explosive crystallization.     

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.     

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.     

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).     

Structural and magnetic properties of CaAl4Fe8O19

A new compound, CaAl₄Fe₈O₁₉, was synthesized for the first time and characterized by X-ray diffraction. It was found to have a hexagonal magnetoplumbite structure with lattice parametersa=5·83 Å andc=22·14 Å. The electrical studies showed that the compound was a semiconductor with energy of activationq=0·86 eV. The magnetic susceptibility was studied in the temperature range 300 K to 850 K, in which the compound was paramagnetic with a Curie molar constant of 31·03.     

Structural and magnetic properties of CaMg2Fe16O27

A new compound, CaMg₂Fe₁₆O₂₇, is synthesized for the first time, in polycrystalline form, using stoichiometric mixture of oxides with standard ceramic technique and characterized by X-ray diffraction. It is found to have a hexagonal W-type structure with lattice parametersa = 5.850 Å andc = 33.156 Å. Electrical studies show that the compound is a semiconductor with energy of activation, ΔE = 0.56 eV. Electrical conductivity results show a transition in the conductivity vs temperature plot near the Curie temperature. The activation energy value obtained for the paramagnetic phase is found to be higher than that of the ferrimagnetic phase. The molar magnetic susceptibility was measured in the temperature range 300–850 K and the results show that the compound is ferrimagnetic at room temperature. The compound also shows hysteresis at 300 K. Paramagnetic nature of the sample above Curie temperature is also studied. The Curie molar constantC _M bdcalculated from the plot of 1/χ_M vsT(K) bdis found to be nearly in agreement with the expected value.     

Synthesis and structural characterization of CsNiP crystal

CsNiP crystals were synthesized by hydrothermal technique and characterized by the X-ray diffraction method. This alkaline transition metal phosphide crystallizes in the hexagonal system with space groupP6 ₃/mmc and cell parameters,a = 7.173(2) Å,c = 5.944(9) Å,V = 264.87(7) ų andZ = 2. The final residual factor isR1 = 0.0362 for 206 reflections withI > 2σ(I).     

Investigation of the crystallization process and crystal structure of Si-incorporated GeSb phase-change films

The effect of Si incorporation on the crystallization process and crystal structure of Te-free Sb-rich GeSb was investigated in this study. Si concentrations were controlled to 0, 5.1, 9.3, and 12.8 at.% by controlling the sputtering power of the GeSb alloy target (20:80 at.% for Ge:Sb) and Si target. After film deposition, the crystallization process and crystal structure were investigated. Crystallization temperature increased from 320 to 400 °C and the overall crystallinity was decreased with increasing Si concentration. These were analyzed by sheet resistance measurements after thermal annealing and optical contrast measurements by optical static testing. Glass transition temperatures were calculated and increased from 240 to 285 °C with increasing Si concentration. Considering the proportional relation between the glass transition temperature and crystallization temperature, it is thought that more energy is required for crystallization with increased Si concentration. A study of the crystallization process kinetics was conducted by applying the Johnson–Mehl–Avrami model to the optical static test results, which were carried out under a pseudo-isothermal process. The Avrami coefficient was 4.10 and decreased to 3.18 when the crystallization was generated with increased Si concentration from 0 to 12.8 at.%. Therefore, crystallization speed was thought to decrease with increased Si concentration. Based on the results of crystal structure analysis by XRD and HRTEM, the crystal structure of our Sb-rich GeSb PCM was revealed to be a typical Sb structure, i.e., an A7 hexagonal structure with lattice parameters of a = 4.26 Å and c = 11.45 Å. No crystal phase of Ge or Si was observed and no evidence of the structure change in Sb crystals due to Ge or Si incorporation was observed.     

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.     

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°.     

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).     

Crystallization of amorphous antimony films deposited onto glass substrates in ultrahigh vacuum

The crystallization of amorphous antimony (a-Sb) films deposited onto glass substrates in an ultrahigh vacuum of 10^?6?10^?7 Pa is investigated through in situ observation with an optical microscope camera. In comparison with the results for deposition in a conventional vacuum of 10^?4?10^?5 Pa, a marked reduction is observed in the critical thickness d_c for crystallization. For thicknesses less than the previous d_c value of about 250 Å, the dependence of the crystallization rate on the thickness is found to weaken drastically and the activation energy of the atoms for crystallization to increase. The antimony crystallites which nucleate in such thin a-Sb films do not take a simple spherical form.     

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.     

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).     

Study on a novel energetic cocrystal of TNT/TNB

A new energetic cocrystal of TNT/TNB was obtained by evaporating ethanol at room temperature over a period of 3 days. It is found that the donor–acceptor π–π interaction, p–π interaction, and C–H···O hydrogen bond interaction are dominant in the formation of the cocrystal. In this work, physicochemical characteristics of cocrystal have also been studied using several methods: Optical Microscopy, Powder X-ray Diffraction, Single Crystal X-ray Diffraction and differential scanning calorimetry. It is shown that TNT and TNB molecules cocrystallize in a monoclinic system with space group P2₁/c and cell parameters a = 20.4570(8) Å, b = 6.1222(2) Å, c = 15.1635(6) Å, β = 110.091(4)°, and Z = 4. The cocrystal has a crystal density of 1.640 g cm^?3 and H₅₀ (50 % explosion characteristics of drop height) of 112.2 cm, which is higher than that of TNT (100 cm), TNB (77.8 cm) and most of the other explosives. The result shows that co-crystallization may help to improve the performance of TNT and TNB.     

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.     

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.     

Synthesis and properties of LiZr2(AsO4)3 and LiZr2(AsO4) x (PO4)3 − x

The LiZr₂(AsO₄)₃ arsenate and LiZr₂(AsO₄) _x (PO₄)_{3 ? x} solid solutions have been prepared through precipitation followed by heat treatment, and characterized by X-ray diffraction, X-ray structure analysis, IR spectroscopy, and impedance spectroscopy. We have established conditions for the crystallization of the arsenate and a continuous series of arsenate phosphate solid solutions (0 ≤ x ≤ 3), which have been obtained as two polymorphs: monoclinic and hexagonal. Using the Rietveld method, we have refined the crystal structures of the polymorphs of LiZr₂(AsO₄)₃ (sp. gr. P2₁/n, a = 9.1064(2), b = 9.1906(2), c = 12.7269(3) Å, β = 90.844(2)°, V =1065.03(5) ų, Z = 4; sp. gr. R $\bar 3$ c, a = 9.1600(4), c = 22.9059(13) Å, V = 1664.44(14) Å, Z = 6) and LiZr₂(AsO₄)_1.5(PO₄)_1.5. Their structural frameworks are built up of AsO₄ tetrahedra—or (As,P)O₄ tetrahedra occupied by arsenic and phosphorus atoms at random—and ZrO₆ octahedra, with the lithium atoms in between. The ionic conductivity of the materials has been measured. The cation conductivity of monoclinic LiZr₂(AsO₄) _x (PO₄)_{3 ? x} with 0 ≤ x ≤ 1 has been shown to exceed the conductivity of lithium zirconium phosphate.     

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.     

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.