Molecular beam epitaxial growth of zinc-blende FeN(1 1 1) on wurtzite GaN(0 0 0 1)

We report a study of the growth of iron nitride on gallium nitride using molecular beam epitaxy with Fe e-beam evaporation and rf N-plasma growth. Thin iron nitride layers of thickness about 16 nm were grown and monitored in situ using reflection high energy electron diffraction. The samples following growth were analyzed ex situ using a variety of techniques including X-ray diffraction, Rutherford Backscattering, and atomic force microscopy. By monitoring the structure, morphology, and lattice constant evolution of the iron nitride film, the crystal phase and orientation with respect to the GaN substrate are deduced; and from RBS data, the stoichiometry is obtained. The growth is discussed in terms of a 2-D to 3-D growth mode transition, and a critical thickness is estimated.     

Syntheses of metal nitrides, metal carbides and rare-earth metal dioxymonocarbodiimides from metal oxides and dicyandiamide

We design a facile and efficient solid-state reaction method by selecting an organic reagent dicyandiamide and metal oxides as precursors to prepare metal nitrides, carbides and rare-earth metal dioxymonocarbodiimides in sealed ampoules. Some fine divided nitride and carbide nanoparticles with small and uniform size can be easily obtained at the relatively low temperatures. It is interesting to find that dicyandiamide is not only a highly efficient nitridation reagent but also a highly efficient carburization reagent, and can be used as a precursor to directly synthesize rare-earth metal dioxymonocarbodiimides. A possible mechanism is proposed to explain the results of the reactions between the organic reagent and metal oxides.     

Crystal structure, thermal expansion and electrical properties of the new Al0.32ErGe2 compound

A new ternary compound Al_0.32ErGe₂ has been synthesized and studied from 298 K to 773 K using X-ray powder diffraction technique. Its structure has been determined at room temperature by Rietveld refinement of X-ray powder diffraction data. The ternary compound Al_0.32ErGe₂ crystallizes in the orthorhombic with the defect CeNiSi₂ structure type (space group Cmcm, a = 0.40701(2) nm, b = 1.60401(9) nm, c = 0.39240(2) nm, Z = 4 and D_calc = 8.326 g/cm³). The average thermal expansion coefficients , and of Al_0.32ErGe₂ are 1.72 × 10⁻⁵ K⁻¹, 1.11 × 10⁻⁵ K⁻¹ and 1.52 × 10⁻⁵ K⁻¹, respectively. The bulk thermal expansion coefficient is 4.35 × 10⁻⁵ K⁻¹. Electrical resistivity of Al_0.32ErGe₂ was measured between 5 K and 300 K.     

Single crystal preparation and crystal structure of the Cu2Zn/Cd,Hg/SnSe4 compounds

Single crystals of Cu₂Zn/Cd/SnSe₄ were grown using a solution-fusion method. The crystal structure of the Cu₂Zn/Cd,Hg/SnSe₄ compounds were investigated using X-ray powder diffraction. These compounds crystallize in the stannite structure (space group I 2m) with the lattice parameters: a=0.56882(9), c=1.13378(9) nm, c/a=1.993 (Cu₂ZnSnSe₄), a=0.58337(2), c=1.14039(4) nm, c/a=1.955 (Cu₂CdSnSe₄) and a=0.58288(1), c=1.14179(2) nm, c/a=1.959 (Cu₂HgSnSe₄). Atomic parameters were refined in the isotropic approximation (R_I=0.0517, R_I=0.0511 and R_I=0.0695 for Cu₂ZnSnSe₄, Cu₂CdSnSe₄ and Cu₂HgSnSe₄, respectively).     

Red photoluminescence properties and crystal structure of sodium rare earth oxyborate

The subsolidus phase relations of the system Y₂O₃–Na₂O–B₂O₃ are reported. There are seven binary compounds and two ternary compounds in this system. A new ternary compound Na₂Y₂B₂O₇ is identified. The structure has been determined for the compound Na₂Y₂B₂O₇ from powder X-ray diffraction. The lattice constants of P2₁/c for the compound Na₂Y₂B₂O₇ are a=10.5993(1) Å, b=6.2311(1) Å, c=10.2247(1) Å, β=117.756(1)° and z=4. The structure can be described as being made up of isolated BO₃ triangles and YO₈ polyhedra. The photoluminescence properties of Eu ion-doped Na₂Y₂B₂O₇ and Na₃Y(BO₃)₂ show strong red-emission of the ⁵D₀–⁷F₂ transitions at 611 and 615 nm, respectively. The results of emission spectra are in good agreement with the crystallographic study. The relationship between Eu ion content and emission intensity is analyzed too.     

Synthesis of VN nanopowders by thermal nitridation of the precursor and their characterization

Vanadium nitride (VN) nanopowders can be synthesized by thermal nitridation of the precursor of ammonium vanadate (NH₄VO₃) and nanometer carbon black. The products were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) techniques. The results show that the single phase VN powders can be synthesized at 1100 °C for 1 h, and the powders show good dispersion and are mainly composed of uniformly sized spherical particles with a mean diameter of 50 nm. The surface of the specimen mainly consists of V, N, O and C four species elements, the peak core at 397.24 eV corresponds to N 1s of VN. The O 1s peaks with the binding energies of 530.40 eV and 532.15 eV are ascribed to vanadium pentoxide (V⁵⁺) and H₂O (OH⁻), and the contents are very little. The C 1s profile is a single symmetric peak, which mainly comes from the polluted carbon used for the correction of the XPS measurement.     

Preparation, thermal stability, and magnetic properties of Fe---Co---Zr---Mo---W---B bulk metallic glass

A bulk metallic glass (BMG) cylinder of Fe₆₀Co₈Zr₁₀Mo₅W₂B₁₅ with a diameter of 1.5 mm was prepared by copper mould casting of industrial raw materials. The amorphous state and the crystallization behavior were investigated by X-ray diffraction (XRD). The thermal stability parameters, such as glass transition temperature (T_g), crystallization temperature (T_x), supercooled liquid region (ΔT_x) between T_g and T_x, and reduced glass transition temperature T_rg (T_g/T_m) were measured by differential scanning calorimetry (DSC) to be 891, 950, 59 K, and 0.62, respectively. The crystallization process took place through a single stage, and involved crystallization of the phases -Fe, ZrFe₂, Fe₃B, MoB₂, Mo₂FeB₂, and an unknown phase, as determined by X-ray analysis of the sample annealed for 1.5 ks at 1023 K, 50 K above the DSC peak temperature of crystallization. Mössbauer spectroscopy was studied for this alloy. The spectra exhibit a broadened and asymmetric doublet-like structure that indicated paramagnetic behavior and a fully amorphous structure. -Fe was found in the amorphous matrix for a cylinder with a diameter of 2.5 mm. The success of synthesis of the Fe-based bulk metallic glass from industrial materials is important for the future progress in research and practical application of new bulk metallic glasses.     

The crystal structure and magnetic properties of the Gd6Cr4Al43 compound

The crystal structure of intermetallic compound Gd₆Cr₄Al₄₃ has been investigated by means of X-ray diffraction data (Ho₆Mo₄Al₄₃ structure type, space group P6₃/mcm, Pearson symbol hP106, a = 10.9144(7) Å, c = 17.7361(13) Å).

SQUID magnetic measurements carried out for the title compound point to the existence of two antiferromagnetic phase transitions observed at T_N1 = 19.0(1) K and T_N2 = 6.8(1) K, respectively.     

Formation and thermal stability of new Zr–Cu-based bulk glassy alloys with unusual glass-forming ability

The simultaneous addition of Al and Ag to Zr–Cu binary alloys increased in the stabilization of supercooled liquid, the reduced glass transition temperature and γ value, leading to greatly enhance the glass-forming ability (GFA). The Zr–Cu–Ag–Al glassy alloy samples with diameters above 15 mm were obtained in the wide composition range of 42–50 at% Zr, 32–42 at% Cu, 5–10 at% Ag, and 5–12 at% Al. The best GFA was obtained for Zr₄₈Cu₃₆Ag₈Al₈ alloy, and the glassy samples with diameters up to 25 mm were fabricated by an injection copper mold casting. The Zr₄₈Cu₃₆Ag₈Al₈ glassy alloy exhibited high tensile and compressive fracture strength of over 1800 MPa.     

Synthesis, structure, and properties of Li2Pb2CuB4O10 with isolated [CuB4O10] units

The copper borate Li₂Pb₂CuB₄O₁₀ has been synthesized in air by the standard solid-state reaction at temperature in the range 550-650 °C and the structure of Li₂Pb₂CuB₄O₁₀ was determined by single-crystal X-ray diffraction. Li₂Pb₂CuB₄O₁₀ crystallizes in the monoclinic space group C2/c (no. 15) with a = 16.8419(12), b = 4.7895(4), c = 13.8976(10) Å, and β = 125.3620(10)°, V = 914.22(12) Å³, and Z = 4, as determined by single-crystal X-ray diffraction. The Li₂Pb₂CuB₄O₁₀ structure exhibits isolated units of stoichiometry [CuB₄O₁₀]⁶⁻ that are built from CuO₄ distorted square planes and triangular BO₃ groups. The IR spectroscopy and thermal analysis investigations of Li₂Pb₂CuB₄O₁₀ are also presented.     

The effect of dopant Cu, Fe, Ni or La on the structures and properties of mesoporous Co-Ce-O compound catalysts

A series of Co-Ce-O mesoporous catalysts doped with Cu, Fe, Ni or La and the undoped one were synthesized by using tri-block copolymer P-123 as the template. These catalysts show wormhole-like structures, high surface areas (144–167 m²/g) and uniform meso-pore size distributions (4.0–4.8 nm) after calcination at 500 °C. The activity for low-temperature CO oxidation and the thermal stability of the mesoporous Co-Ce-O catalyst are largely modified by the dopant Cu, Fe, Ni or La in different ways. It is revealed by in situ diffuse reflectance infrared spectroscopy that CO oxidation over all the samples except the Ni-doped one undergoes carbonates pathway. In this case, the oxidation activities of the catalysts are mainly determined by the mobility of surface lattice oxygen species, which is indicated by the temperature-programmed reduction and desorption results. Doping with Cu greatly enhances the oxidation activity of Co-Ce-O catalyst at the calcination temperatures of 500 °C and 650 °C, and doping with La significantly improves its activity at the calcination temperature of 800 °C. However, doping with Fe always decreases the activity of Co-Ce-O catalyst regardless of the calcination temperature. Largely different from other dopants, the addition of Ni induces a change of the mechanism for CO oxidation and results in a remarkable decrease in the activity.     

Ba3YB3O9: phase transition and crystal structure

A new modification of the compound Ba₃YB₃O₉, β phase, has been attained through solid phase transition from phase at 1125–1134 °C. β-Ba₃YB₃O₉ crystallizes in the hexagonal space group with cell parameters a=13.0529(8) Å, c=9.5359(9) Å. The crystal structure of -Ba₃YB₃O₉ has been determined from powder X-ray diffraction (XRD) data. The refinement was carried out using the Rietveld methods and the final refinement converged with R_p=8.8%, and R_wp=11.8% with R_exp=5.65%. In its structure, the isolated [BO₃]³⁻ anionic groups are parallel to each other and distributed layer upon layer along the c-axis. The Y atoms are six-coordinated by the O atoms to form octahedra. The result of IR spectrum confirmed the existence of [BO₃]³⁻ triangular groups.     

Crystal structure of the Ag2SiS3 compound

The crystal structure of the ternary compound Ag₂SiS₃ was determined on the basis of X-ray powder diffraction. The compound belongs to a new structure type, space group P2₁/c, a = 0.66709(1), b = 0.66567(2), c = 1.31748(3) nm, and β = 118.658(1)°. Ag₂SiS₃ contains isolated [Si₂S₆] anionic units consisting of pairs of edge-shared tetrahedra. The Ag atoms are situated in the interstices formed by these fragments.     

Observation of octahedral tilted in Sr0.5TaO3 prepared by nanosheet processing: An EXAFS study

The metastable crystal structure of Sr_0.5TaO₃ with pseudo-cubic structure was investigated by X-ray diffraction analyses and extended X-ray absorption fine structure. Sr_0.5TaO₃ powders were synthesized from the host material of H₂Sr_1.5Ta₃O₁₀ by direct dehydration and nanosheet processing. The structure of Sr_0.5TaO₃ is suggested based on X-ray diffraction analyses, while the local structural analyses by extended X-ray absorption fine structure clearly reveals a tilted of TaO₆ octahedra in Sr_0.5TaO₃. It is indicated that planar defects resulting from stacking faults in nanosheet-derived H₂Sr_1.5Ta₃O₁₀ are possibly the cause of the larger tilted of TaO₆ octahedra in Sr_0.5TaO₃ (Ta–O–Ta bond angle (164°)) prepared by nanosheet processing compared with Sr_0.5TaO₃ (Ta–O–Ta bond angle (169°)) obtained by direct dehydration.     

Fabrication and electrical and thermal properties of Ti2InC, Hf2InC and (Ti,Hf)2InC

In this paper we report on the characterization of predominantly single phase, fully dense Ti₂InC (Ti_1.96InC_1.15), Hf₂InC (Hf_1.94InC_1.26) and (Ti,Hf)₂InC ((Ti_0.47,Hf_0.56)₂InC_1.26) samples produced by reactive hot isostatic pressing of the elemental powders. The a and c lattice parameters in nm, were, respectively: 0.3134; 1.4077 for Ti₂InC; 0.322, 1.443 for (Ti,Hf)₂InC; and 0.331 and 1.472 for Hf₂InC. The heat capacities, thermal expansion coefficients, thermal and electrical conductivities were measured as a function of temperature. These ternaries are good electrical conductors with a resistivity that increases linearly with increasing temperatures. At 0.28 μΩ m, the room temperature resistivity of (Ti,Hf)₂InC is higher than the end members (0.2 μΩ m), indicating a solid solution scattering effect. In the 300 to 1273 K temperature range the thermal expansion coefficients are: 7.6×10⁻⁶ K⁻¹ for Hf₂InC, 9.5×10⁻⁶ K⁻¹ for Ti₂InC, and 8.6×10⁻⁶ K⁻¹ for (Ti,Hf)₂InC. They are all good conductors of heat (20 to 26 W/m K) with the electronic component of conductivity dominating at all temperatures. Extended exposure of Ti₂InC to vacuum (10⁻⁴ atm) at 800 °C, results in the selective sublimation of In, and the conversion of Ti₂InC to TiC_x.     

Synthesis, optical and dielectric studies on novel semi organic nonlinear optical crystal by solution growth technique

Bisthiourea lead acetate Pb[SC(NH₂)₂]₂(CH₃COO)₂), a novel semi organic non linear optical crystal having dimensions 17 mm × 2 mm × 2 mm were grown using slow evaporation technique. The lattice parameters for the grown crystals were determined using single crystal XRD. The presence of functional groups for the grown crystals was confirmed using Fourier transform infrared (FT-IR) spectroscopy. The optical absorption studies show that the material has wide optical transparency in the entire visible region. The dielectric constant and dielectric loss has been studied as a function of frequency for various temperatures and the results were discussed in detail. The second harmonic generation was confirmed by Kurtz powder method and it is found to be 5 times than that of potassium dihydrogen phosphate (KDP) crystal.     

Contribution to the investigation of ternary Lu-Ni-Sn system

The phase equilibria in the Lu-Ni-Sn ternary system were studied at 770 K (up to 50 at.% Sn) and 670 K (more than 50 at.% Sn) by means of X-ray and metallographic analyses in the whole concentration range. The Lu-Ni-Sn system is characterized by formation of 10 ternary intermetallic compounds at investigated temperatures: LuNi₅Sn (CeCu₅Au-type), LuNi₄Sn (MgCu₄Sn-type), Lu₆Ni₂Sn (Ho₆Co₂Ga-type), Lu₂Ni₂Sn (Mo₂FeB₂-type), LuNi₂Sn (MnCu₂Al-type), LuNi_2−xSn (YbNi_2−xSn-type), LuNiSn (TiNiSi-type), LuNiSn₂ (LuNiSn₂-type), Lu₂NiSn₆ (Lu₂NiSn₆-type), and LuNiSn₄ (LuNiSn₄-type). Three new binary compounds, LuNi₃ (PuNi₃-type), Lu₃Ni₂ (Er₃Ni₂-type), and Lu₃Ni (Fe₃C-type), were found in the Lu-Ni system.     

Surface and in-depth characterization of InGaN compounds synthesized by plasma-assisted molecular beam epitaxy

InGaN layers with multiple quantum wells are widely used as active layers in advanced optoelectronic devices. In the present work, surface properties of some InGaN layers grown on GaN/sapphire substrates by plasma-assisted molecular beam epitaxy were examined. The total indium content incorporated in the crystalline lattice of In_0.165Ga_0.835N and In_0.353Ga_0.647N layers grown with a thickness of 70-200 nm was controlled by the growth temperature, and was determined from X-ray diffraction. Auger electron spectroscopy and X-ray photoelectron spectroscopy analysis reveal relatively smaller concentration of In within the surface area than in the bulk of the InGaN layers. The Ar⁺ XPS depth profile analysis shows the thick InGaN layers to be chemically homogeneous within an analytical area. To determine the electron inelastic mean free path in the layers within the 500-2000 eV range, relative elastic-peak electron spectroscopy measurements with Ni and Au standards were performed. The measured IMFPs were considerably larger than those predicted from the TPP-2M formula. The smallest root-mean-square-deviation and the mean percentage deviation of 9.9 Å and 44.5%, respectively, were found between EPES IMFP data and those predicted for the In_0.353Ga_0.647N layer with respect to the Au standard. This work provided the detailed compositional and chemical changes of InGaN thick layers, and could be useful in solving key issues associated with the growth of high-quality layer with much higher In content.