[en] Phase separation of bulk and ribbon Pd₄₀Cu₃₀Ni₁₀P₂₀ glasses, annealed in the supercooled liquid region at ambient pressure and high pressures, has been studied by means of differential scanning calorimetry (DSC) and X-ray diffraction techniques. DSC measurements show only one glass transition event in all annealed samples, indicating that no phase separation occurs in the alloy annealed in the supercooled liquid region. Phase analyses reveal at least six crystalline phases in the crystallized sample: monoclinic, tetragonal Cu₃Pd-like, rhombohedral, fcc-Ni₂Pd₂P, fcc-(Ni, Pd) solid solution, and body-centered tetragonal (bct) Ni₃P-like phases. Annealing treatments under external pressures in the vicinity of the glass transition temperature neither induce phase separation nor alter the glass transition temperature of the Pd₄₀Cu₃₀Ni₁₀P₂₀ bulk glass

[en] Metastable α-Fe₂O₃-MO₂(M: Sn and Ti) solid solutions can be synthesized by mechanical alloying. The alloy formation, microstructure, and gas sensitive properties of mechanically milled α-Fe₂O₃-SnO₂ materials are discussed. Tin ions in α-Fe₂O₃ are found to occupy the empty octahedral holes in the α-Fe₂O₃ lattice. This interstitial model can also describe the structure of α-Fe₂O₃-TiO₂solid solutions. Finally, a correlation of gas sensitive properties with microstructure of α-Fe₂O₃-SnO₂ materials is presented

[en] In this work, we present a study on the magnetic behavior of CuFe₂O₄ nanoparticles with different particle sizes. Magnetic particle size distribution obtained from M(H) curves in the superparamagnetic (SPM) state showed good agreement with data obtained from X-ray powder diffraction. Field-cooled and zero-field-cooled magnetization data showed a blocking temperature T_B∼225 K, independent of particle size, which is associated to interparticle interactions. It was observed that T_B and the irreversibility temperature T_irr, shift to lower temperature with increasing applied fields, both with an H^-1 dependence. Strong training effects were observed from relaxation data, assigned to the irreversible behavior of the spin-disordered particle surface. The magnetic viscosity at T=4.2 K was analyzed for sample with D_mean=7.7 nm, revealing strong irreversibility after each major hysteresis loop. These results are discussed in terms of multiple spin-disordered configurations, at particle surface, with quasidegenerate states

[en] Typically, wavelength instabilities at synchrotron beams are largely due to thermomechanical phenomena at the primary-beam monochromators and fluctuations of the synchrotron orbit. Although they are small, they may have a negative influence on some kinds of diffraction experiments, for example in thermal expansion studies. Using a wavelength calibration procedure is a natural way of solving or at least reducing this problem. Diamond can be used as a calibration material because of its known low-thermal expansion and low X-ray absorption. Low-temperature X-ray powder diffraction measurements were carried out at the powder diffractometer at the B2 beamline at Hasylab/DESY (Hamburg). The cryostat ensured a good temperature stability and accuracy. Unit-cell parameters for cubic (spinel-type) silicon nitride, c-Si₃N₄, and for copper indium selenide, CuInSe₂, were determined in the temperature range from 14 up to 302 K. An improvement of the data quality due to elimination of the wavelength fluctuation effect is demonstrated

[en] A new buncher system consisting of two bunchers has been designed and constructed for HIRFL injector cyclotron, working at the SFC acceleration modes of H=1 and H=3, respectively. The bunchers use saw-tooth RF waveform, but with double-gap drift tube electrodes and single-gap grid electrodes, respectively. The special merit of the design is introduction of the half-frequency bunching mode, utilizing half of the cyclotron RF frequency. With this method, a perfect longitudinal match between the injector SFC and the main cyclotron SSC has been reached theoretically, compared to the original efficiency of 50% for most cases. Detailed studies have been made concerning space charge effects, longitudinal dispersions through the yoke hole and the spiral inflector, and non-linearity in both the RF waveform and the stray electric field of electrodes

[en] Atomic packing of three Fe-based metallic glasses (MGs) has been studied by X-ray diffraction and X-ray absorption fine structure, combining with reverse Monte Carlo (RMC) and ab initio molecular dynamics (AIMD) simulations. It is found that the addition of Y and Nb atoms to the binary Fe–B MG mainly stabilizes large high-coordinated polyhedra by substituting the center Fe atoms, promoting the formation of icosahedron-like clusters and their connectivity with high-coordinated polyhedra. Moreover, the heterogeneities in local structures are found to increase due to element segregations of Fe, Y and Nb atoms. The obtained results indicate that the large-sized Y and Nb atoms can frustrate the geometry of competing crystalline phases and improve the atomic packing efficiency, therefore leading to the enhanced glass forming ability.

[en] Highlights: •A new La-based bulk metallic glass is developed that has a pronounced secondary β-relaxation and critical size at least 10 mm in diameter. •The β-relaxation becomes more pronounced with increasing annealing time due to decoupling from the α relaxation. •A relationship between the coupled angle of two relaxations and the shear-transformation-zone (STZ) volume is established. •The correlation of β-relaxation with the ambient compressive plasticity of bulk samples is not revealed. -- Abstract: A pronounced secondary β-relaxation is observed in a newly-developed La-based bulk metallic glass that has critical size at least 10 mm in diameter. It is demonstrated that the β-relaxation becomes pronounced with increasing annealing time due to decoupling from the α relaxation. By using nanoindentation, we find that the shear-transformation-zone (STZ) volume and involved atoms increase in the annealed samples, implying that the decoupling of the β-relaxation from the α relaxation can promote the movement of local atoms. However, the correlation of β-relaxation with ambient compressive plasticity of bulk samples is not revealed

[en] It is shown that a double-Gaussian-shaped probability distribution of moment directions is an adequate model of the spin structures in as-cast, stress-relieved and field-annealed samples of Fe₇₈B₁₃Si₉ at room temperature and in zero applied field. The distribution comprises the convolution of two independent Gaussian distributions, one in the ribbon plane, and the other normal to the ribbon plane. The double-Gaussian distribution is more physically realistic than some alternative models of the moment distribution in amorphous metals. (orig.)

[en] The hardness and thermal stability of cubic spinel silicon nitride (c-Si₃N₄), synthesized under high-pressure and high-temperature conditions, have been studied by microindentation measurements, and x-ray powder diffraction and scanning electron microscopy, respectively. The phase at ambient temperature has an average hardness of 35.31 GPa, slightly larger than SiO₂ stishovite, which is often referred to as the third hardest material after diamond and cubic boron nitride. The cubic phase is stable up to 1673 K in air. At 1873 K, α- and β-Si₃N₄ phases are observed, indicating a phase transformation sequence of c-to-α-to-β-Si₃N₄ phases. (author). Letter-to-the-editor

[en] The structure of Al₈₈Y₇Fe₅ metallic glass has been investigated by differential scanning calorimetry, x-ray powder diffraction, and x-ray absorption fine structure (XAFS) techniques. The amorphous alloy crystallizes according to the following scheme: amorphous →α-Al+ residual amorphous →α-Al+Al₃Y+AlFeY. The atomic structure of the amorphous alloy was modeled by reverse Monte Carlo methods. The resulting structure indicates that the prepeak (at 1.42 A ring ^-1) in the static structure factor S(Q) is caused by contributions of distinct Y-Y, Y-Fe pairs. From the analysis of our XAFS spectra at the Fe and Y K edge the following characteristics of the local structure are found: The interatomic distance between Fe and coordinated Al atoms in the amorphous state is significantly (8.9%) shorter than the sum of the nominal metallic-state radii. The average coordination number is anomalously 36% reduced compared to the value derived from the dense-random-packing (DRP) model, using again the nominal metallic-state radii. On the other hand, the Y-Al distance as well as the number of Al atoms coordinating Y is close to the values predicted by the DRP model. These anomalous changes around the Fe atoms indicate a strong interaction between Fe and Al, which corroborate a covalent bonding. In connection with the values obtained from the XAFS data analysis, the effective atomic radii in the amorphous phase have been calculated. Consequently, applying them to the calculation of the atomic size factor (λ=0.1076) confirms that Al₈₈Y₇Fe₅ follows the rule of atomic size ratio for glass formation