Hydrogen-induced magnetic and structural transformations of GdCu

The magnetization of GdCu induced by hydrogen uptake was measured within the temperature range of 4.2 to 300 K, occurring phase changes were followed by X-ray diffraction measurements at ambient temperature. The prepared GdCu powder of CsCl-type structure readily absorbed hydrogen at ambient temperature, where hydrogen pressure was below 100 kPa. Hydrogenation changed the magnetism of GdCu in a complex manner from an antiferromagnetic-like type to a paramagnetic-like one. The changes in magnetic properties of GdCu by hydrogenation are governed by hydrogen-induced disproportionation. Within the composition range 0<[H]/[GdCu]<1, GdCu disproportionated according to 2GdCu+H₂→GdH₂+GdCu₂ . The magnetization was evaluated by the expression χ_total=(1-x)χ_GdCu+(x/2)(χ_GdH2+χ_GdCu2). GdCu hydride was not observed. Hydrogenation beyond [H]/[GdCu]>1 gave rise to the disproportionation of GdCu₂ causing the change in magnetization.     

One convenient synthesis route to boron nitride nanotube

We describe one convenient synthesis route to boron nitride (BN) nanotube by the reaction of boron powder, iron oxide, and ammonium chloride at 600 °C for 12 h. Characterized by XRD, FTIR, XPS, TEM and SAED, the composition and morphology of the products are confirmed. The possible reaction mechanism is also discussed.     

Structural and Thermodynamic Properties of M3W3N （M=Fe,Co, Ni）

Ternary transition metal nitrides, Fe3 W3N, Coa W3N, and Nia WaN~ are studied by the use of interatomic potentials acquired from lattice inversion. The study indicates that Fe3 WaN would be more stable than the other compounds in the family of intermetallic tungsten nitrides. The investigation of phonon density of states indi- cates that the lower frequency modes are mostly excited by the metal atoms, and the higher frequency modes are mostly excited by the nitrogen atoms. A qualitative analysis is carried out with the relevant potentials for the phase stability and vibrational modes.     

Electrical properties and stability of Tb-doped zinc oxide-based nonlinear resistors

The microstructure, electric field-current density (E-J), capacitance-voltage (C-V), and stability characteristics of Zn-Pr-Co-Cr-Tb oxide-based nonlinear resistors were investigated for different Tb₄O₇ amounts. It increased in the range of 8.9-42.0 in the nonlinear coefficient and in the range of 1026-6514 V/cm in the breakdown field with increasing Tb₄O₇ amount. As Tb₄O₇ amount increased, the donor density decreased in the range of 1.23×10¹⁸-0.70×10¹⁸/cm³, whereas the barrier height at grain boundaries increased in the range of 0.73-0.93 eV. A good stability was obtained in the range of 0.25-0.5 mol% in Tb₄O₇ amount.     

Investigation of phase-equivalent potentials by a halo transfer reaction

Using the supersymmetric quantum mechanics, we investigate the wave function-sensitive properties of the supersymmetric potentials which have received a lot of attention in the literature recently. We show that a superdeep potential and its phase-equivalent shallow-partner potential give very similar rms radius values for the weakly bound systems such as the deuteron and ¹¹Be nuclei. Although the corresponding eigenstates differ in the node-number, our investigation on the ¹¹Be(p, d )¹⁰Be single nucleon halo transfer reaction at 35 MeV show that also other physical quantities such as the cross-section angular distributions calculated using these wave functions reflect the nodal structure rather weakly. This lends support to two nearly equivalent treatments of the Pauli principle. Received: 15 May 2000 / Accepted: 14 September 2000     

Properties of poly(2-hydroxyethyl acrylate)-silica nanocomposites obtained by the sol-gel process

Poly(2-hydroxyethyl acrylate) swollen in water forms a hydrogel with good biological acceptance but poor mechanical properties. Reinforcement by a nanometric silica phase obtained by acid catalyzed sol-gel reaction of tetraethoxysilane occurring simultaneously with the polymerization of the organic polymer leads to a hybrid material and is a way to improve the mechanical properties of the homopolymer. Dynamic mechanical measurements show a stiffness increase in the rubbery state as the silica content is increased, for both the xerogel (dry) and the swollen samples. Density measurements of the hybrid materials show that the silica phase has an apparent density close to that of vitreous silica, thus giving an indication of the intimate interpenetration of the organic and the inorganic phases in these nanocomposites. Thermogravimetric analysis has been used to probe the dependence of the thermal stability of the samples on the silica content, and to determine the actual silica amounts in each sample. Information about the percolation threshold of the silica phase could be gained from measurements of water uptake and mechanical moduli. All the results pointed out that the co-continuity of matrix and reinforcement starts at around 15 wt% of silica content.     

From nitride to carbide: control of zirconium-based hard materials film growth and their characterization

High-quality thin films of ZrC_yN_1-y and the novel tribological material Zr_0.8Al_0.2C_yN_1-y have been grown by pulsed reactive crossed-beam laser ablation using Zr and Zr–Al ablation targets, respectively, and a pulsed gas. The gas mixture provided the carbon and nitrogen for the solid-solution films. Control of the stoichiometry (i.e. y) was determined by the relative partial pressures of the nitrogen- and carbon-containing gases. It was found that optimal control of the film chemistry was achieved by using the least thermally reactive gases. In this manner, it was possible to activate the gas species exclusively by collisions in the gas phase with the ablation-plume particles, thereby decoupling the chemistry from surface processes. The films were characterized for their chemical, crystallographic, optical, and tribological properties. All the films had very low impurity levels and a cubic rock salt crystal structure over the entire investigated temperature range between 100 and 600 °C. Exceedingly high quality epitaxial films could be grown on MgO (001) at 600 °C. Films grown on stainless steel were polycrystalline. The hardness of the films showed a maximum for both sets for stoichiometries predicted by a recent theoretical model for hardness based on band-structure calculations. In addition, all the films had an exceptionally low coefficient of friction versus steel. Received: 22 August 2001 / Accepted: 3 March 2002 / Published online: 19 July 2002     

Structural analysis of Cd-Te-O films prepared by RF reactive sputtering

Crystalline and microcrystalline Cd-Te-O samples have been obtained by RF reactive sputtering from a CdTe target using N₂O as oxidant. The growth conditions were substrate temperatures of 323 K, 573 K and 773 K and cathode voltage of −400 V, corresponding to 30 W of forward power. The samples were studied by micro-Raman spectroscopy, X-ray diffraction and optical transmittance. The films are remarkably transparent in the visible range, with transmittances about 88% at 400 nm and band gap energies above the absorption edge of the glass substrates. Although only the samples prepared at 773 K present defined diffraction peaks, the analysis of the Raman spectra indicate that samples prepared at 323 K and 573 K have a defined microstructure indeed. The spectra fitting performed by comparison with pattern compounds demonstrate that Cd-Te-O films are formed of Te-O units similar to those present in metal oxide-doped tellurite glasses, such as TeO₃ and TeO_3 + 1 linked through Cd-O bonds. As the substrate temperature increases the microstructure evolves from a γ-TeO₂ richer state to Cd_xTe_yO_z. In the crystalline sample the main phase identified was CdTeO₃ even though evidence of other phases was observed.     

The effect of thermal annealing on the structural and mechanical properties of a-C:H thin films prepared by the CFUBM magnetron sputtering method

a-C:H films were prepared by closed-field unbalanced magnetron (CFUBM) sputtering on silicon substrates using argon (Ar) and acetylene (C₂H₂) gases, and the effects of post-annealing temperature on structural and mechanical properties were investigated. Films were annealed at temperatures ranging from 300 °C to 700 °C in increments of 200 °C using rapid thermal annealing equipment in vacuum ambient. Variations in microstructure were examined using Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Surface and mechanical properties were investigated by atomic force microscopy (AFM), nano-indentation, residual stress tester, and nano-scratch tester. We found that the mechanical properties of a-C:H films deteriorated with increased annealing temperature.     

Synthesis, structure and luminescence of LaSi3N5:Ce phosphor

In this work, new LaSi₃N₅:Ce³⁺ phosphors have been synthesized by solid-state reaction. Rietveld refinement of the crystal structure of La_1−xCe_xSi₃N₅ reveals that Ce atoms substituted for La atoms occupy 4a crystallographic positions. Broad emission and excitation bands observed were attributed to the transitions between the doublet ground state of the 4f¹ configuration and the crystal field components of the 5d¹ excited state. At 77 K, the centroid and crystal field splitting ε_cfs of the 5d levels of Ce³⁺ in LaSi₃N₅:Ce³⁺ compounds were valuated at 33.4×10³ and 11.3×10³ cm⁻¹, respectively. The zero-phonon line and the Stokes shift were measured to be 26.0×10³ and 5.0×10³ cm⁻¹, respectively.