The dielectric function of Mgy NiHx thin films ()

Mg_y Ni (2≤y≤10) thin films covered with a Pd cap layer are hydrogenated in 10⁵  Pa H₂ between room temperature and 80 ° C and their dielectric function is determined from reflection and transmission measurements. The hydrogenated Mg_y NiH_x thin films show a continuous shift of the optical absorption towards higher photon energies with increasing y. Comparison of the obtained dielectric functions with predictions from an effective medium theory show that a considerable doping of the Mg₂ NiH₄ host takes place at least for y≤3.5 while no signature of MgH₂ is observed in that composition range in the optical spectra. This is in contrast to the predictions from the bulk phase diagram where a mixture of semiconducting Mg₂ NiH₄ (energy gap E_g=1.6  eV) and MgH₂ (E_g=5.6  eV) is expected.     

Extrinsic and intrinsic magnetic properties of Co1−x Fex Sb3

We report magnetic properties of iron in Co_1−x Fe_x Sb₃ for x in the range 0<x<0.2, since x=0.2 is found to be the limit of solubility of iron in the skutterudite lattice. The magnetic ions diluted in the matrix carry a small magnetic moment reduced to that of the spin-only S=1/2 value of the Fe³⁺ in the low spin d⁵ configuration in presence of a strong crystal field that screens the orbital momentum. The magnetic properties give evidence that a small fraction of iron is spin-frozen in magnetite ferrimagnetic clusters, and antiferromagnetic FeO clusters. Because both types of clusters represent only very minor phases, their detection by the usual analytical means such as X-rays is not possible. The remaining part is diluted in the matrix to form a semimagnetic semiconductor characterized by a Fe–Fe nearest-neighbor exchange interaction J that is antiferromagnetic, with |J|/k_B19.6  K.     

Two polymorphs of Ba3Sn2P4: Single crystal and electronic structures

Two polymorphs (I and II) of Ba₃Sn₂P₄ have been found in the same preparative batch. Both compounds crystallize in the centrosymmetric monoclinic space group P2₁/c (#14, a = 7.8669(2) Å, b = 19.2378(5) Å, c = 7.8472(2) Å, β = 112.77(1)°, V = 1095.06(5) Å³, Z = 4, and R/wR = 0.0303/0.0710 for I; a = 7.8771(3) Å, b = 19.4099(7) Å, c = 7.7040(3) Å, β = 112.44(1)°, V = 1088.67(7) Å³, Z = 4, and R/wR = 0.0224/0.0415 for II). Both structures consist of one-dimensional chains separated by Ba²⁺ cations. The isolated chain consists of condensed ethane-like [Sn₂P₆] units. In polymorphs I and II, the condensation and connectivity of the [Sn₂P₆] units are quite different. While [Sn₂P₆] units form four- and six-membered rings in I, they form the five-membered rings in II. The electronic structure calculations indicate that semiconducting behavior is expected for both compounds.     

Synthesis characterization of magnetic properties in La0.7−x Lnx Pb0.3 MnO3 (, Nd, Gd, Dy, Sm and Y) perovskite compounds

The influence of La substitution by rare-earth elements on the magnetization behaviors of perovskite oxides, La_0.7−x Ln_x Pb_0.3 MnO₃ (Ln=Pr, Nd, Gd, Dy, Sm and Y), is investigated. The replacement of La ion by Pr, Nd, Gd, Dy, Sm or Y results in a considerable decrease in the ferromagnetic ordering temperature T_C and clearly irreversible behavior in the FC–ZFC curves showing a short-range spin order phase. The fact is in agreement with the smaller ionic radii of Pr, Nd, Gd, Dy, Sm and Y ions in contrast to La ion and the corresponding larger distortion of perovskite structures. The saturation magnetization M_S increases as Pr or Nd content increases while M_S decreases as Sm or Y content increases. Moreover, the saturation magnetization M_S increases and then decreases as Gd or Dy content increases. These results can be explained in terms of the competition between the increase of ferromagnetically interacting spins due to the introduction of magnetic ions with f-shell electrons and suppression of ferromagnetism due to structure tuning induced by the small ionic radius of the interpolated cation into the La-site.     

The effect of substitution of La for Tb on some physical properties of Tb1−xLaxNi2 solid solutions

The standard Gibbs energy of formation, , of MgLa in the temperature range from near absolute 0 to 525 K were determined by calorimetry. The heat capacities, C_p, from 2 K to 525 K were measured by the relaxation method and DSC. Also, a thermal anomaly at 5.9 K, which appeared to be a superconductive phase transition, was found in the obtained C_p values. The values were determined by combining the C_p data with the standard enthalpy of formation at 298 K which was measured by the Calvet-type calorimeter using hydrochloric acid solution. From 2 to 300 K, the increases gradually, and it can be evaluated as a linear function of temperature above 300 K as follows:

This result is expected to be useful as basic thermodynamic data of Mg-based alloys.     

Crystal structure, thermal expansion and magnetic properties of new compound Dy1.2Fe4Si9.8

The new ternary compound Dy_1.2Fe₄Si_9.8 have been prepared and studied by means of X-ray powder diffraction technique and vibrating sample magnetometer. The ternary compound Dy_1.2Fe₄Si_9.8 crystallizes in the hexagonal Er_1.2Fe₄Si_9.8-type structure, space group P6₃/mmc (no. 194) with lattice parameters a = 0.39415(1) nm and c = 1.52771(3) nm. The crystal structural refinement of the compound Dy_1.2Fe₄Si_9.8 has been performed by using Rietveld method. Lattice thermal expansion studies on the compound were carried out in the temperature range from 298 to 1013 K. The variation of the unit cell parameters shows that the unit cell parameters increase with the increase in temperature. The coefficients of average lattice thermal expansion along various axes in the temperature range from 298 to 1013 K are , and . The temperature dependence of the magnetization for the compound was also investigated in the range from 90 to 300 K. The experimentally determined magnetic effective paramagnetic moment is μ_eff = 11.3μ_B per formula unit (10.3μ_B per Dy atom).     

Fragility and thermal stability of Pt- and Pd-based bulk glass forming liquids and their correlation with deformability

The fragility parameter m of (Pt or Pd)–(Ni, Cu)–P bulk metallic glasses (BMGs) was characterized and compared to other systems. The results indicate that the Pt₆₅Ni₁₅P₂₅ alloy is the most fragile and thermally stable at the supercooled liquid state, thus is the most workable among the presently developed BMGs. To express the degree of workability, a deformability is introduced then correlated with m and the reduced thermal stability . A master curve in term of and has been established for various BMGs, d^* thus can be uniquely related to .     

Kinetic study on Li2.8(V0.9Ge0.1)2(PO4)3 by EIS measurement

Kinetics for lithium ion transfers in the fast ionic conductor Li_2.8(V_0.9Ge_0.1)₂(PO₄)₃ prepared by solid-state reaction method has been studied by electrochemical impedance spectroscopy (EIS) at various temperatures and the results were correlated with observed cathodic behavior. The specific conductivities of Li_x(V_0.9Ge_0.1)₂(PO₄)₃ (x = 0.9–2.8) versus temperatures were analyzed from blocking-electrodes by Wagner's polarization method and the activation energy was calculated. It was observed that electronic conductivities of Li_x(V_0.9Ge_0.1)₂(PO₄)₃ increased with lithium contents in the materials. The compounds show a reversible capacity of 131 mAh g⁻¹ at low current density (13 mA g⁻¹). Modeling the EIS data with equivalent circuit approach enabled the determination of charge transfer and surface film resistances. The Li ion diffusion coefficient (D_Li⁺) versus voltage plot shows three valleys during the first charge cycle coinciding with the irreversible plateau of the voltage versus lithium content profiles reflecting the irreversible phase change in the compound. The obtained D_Li⁺ from EIS varies within 10⁻⁸ to 10⁻⁷ cm² s⁻¹, so Li_2.8(V_0.9Ge_0.1)₂(PO₄)₃ shows excellent chemical diffusion performance.     

Modification to the composition of nanocrystalline RuO2 through reactive milling under O2

Crystalline ruthenium dioxide (RuO₂) has been ball-milled in an O₂ atmosphere and the changes in the physico-chemical properties induced by different milling atmospheres (Ar and O₂) or milling sequences have been established. Cyclic voltammetry and BET measurements were used to evaluate the electrochemically active surface charge (, expressed in C g⁻¹) and the specific surface area (expressed in m² g⁻¹), respectively. The extent of oxygen uptake in the processed samples was determined by X-ray photoelectron spectroscopy (XPS). The value of RuO₂ milled under O₂ for 30 h (sample S4) is 120.7 C g⁻¹, a factor of two higher than the value of RuO₂ milled under Ar for the same period of time (sample S1, 60.3 C g⁻¹). A still higher value is obtained when the O₂ atmosphere of the crucible is frequently replenished (sample S5, 138.7 C g⁻¹) or when the milling operation is prolonged up to 81 h (sample S6, 160.5 C g⁻¹). These changes are paralleled by a variation of the BET surface area, which increases from 24 m² g⁻¹ for sample S1 to 51.5 m² g⁻¹ for sample S5. The concentration ratio [O_{bound to Ru}]/[Ru] determined by XPS increases steadily from sample S1 to sample S6, indicating that the amount [O_{bound to Ru}] increases with the exposure of RuO₂ to oxygen during the milling process. All these changes are explained by the fact that freshly exposed RuO₂ surfaces created during the milling process react with O₂ molecules, thereby lowering the surface energies and the tendency of the milled material to cluster into larger aggregates.     

Growing ledge structures of AlN crystals in a Fe–Mn–Al–C alloy

The Fe–30.4Mn–8.7Al–1.0C (wt.%) alloy was nitridized at 1000 °C. The AlN formed into a Widmanstätten side-plate shape. The side-plate of the AlN is parallel to the basal plane of the HCP crystal. There are three possible growing riser planes; namely ()_AlN, ()_AlN, and ()_AlN planes. The angle for growing riser planes met on the (0 0 0 1) terraces is 120°.     

EXAFS Debye–Waller factors of La and Ni in LaNi5

XAFS measurements of the La L₃ and Ni K-edges for LaNi₅ were done at temperatures of 20, 100, 200 and 293 K. The temperature dependences of the Debye–Waller factors e^−2σ2k2 for La and Ni are deduced. The results show that mean square fluctuation in interatomic distance σ² of La for LaNi₅ is fairly large and the Debye temperature Θ_D of La changes with temperature. These results indicate that the La atom with large atomic size changes its atomic position easily in LaNi₅. The large σ² value of A (rare earth) elements for AB₅ compounds might be correlated to their high capability of the hydrogen absorption and desorption.     

Structural, electrical and magnetic properties of xNiFe2O4 + (1 − x)Ba0.8Sr0.2TiO3 ME composites

Magnetoelectric composites, namely xNiFe₂O₄ + (1 − x)Ba_0.8Sr_0.2TiO₃ were prepared by standard double sintering ceramic method. The X-ray diffraction measurements were carried out to check the phase purity and to calculate the lattice constants. scanning electron microscopy (SEM) micrographs were taken to understand the microstructure of the samples. Dielectric property such as dielectric constant (ε^′) was also studied as a function of frequency in the range 100 Hz–1 MHz. The ac conductivity as a function of frequency and dc resistivity as a function of temperature were studied for different compositions. The hysteresis measurements were done to determine saturation magnetization (M_s) and coersivity (H_c) and magnetic moment was calculated. Effect of resistivity on ME voltage coefficient is studied.     

Properties of exchange biased Co/Co3O4 bilayer films

Co/Co₃O₄ bilayer films were fabricated by RF sputtering with Co and Co₃O₄ targets. Exchange bias effect in the bilayer films was observed at 80 K by vibrating sample magnetometer. The bias effect disappeared about 240 K slightly lower than the Néel point of CoO and much higher than the Néel temperature of Co₃O₄ about 40 K. To clarify the origin of the exchange bias effect, Auger and X-ray photoelectron spectroscopy were employed and CoO was found at a transition region from Co₃O₄ layer to Co layer due to oxygen diffusion during sputtering. The angular dependence of exchange bias field H_E was obtained to obey function of H_E(θ)=18.06 (kA/m)[−cos θ+0.22 cos 3θ+0.03 cos 5θ−0.01 cos 7θ+].     

Synthesis, structural, magnetic and electrical properties of La1−xCdxMnO3 manganites (0.1 ≤ x ≤ 0.5)

Cd-substituted LaMnO₃ compounds have been prepared using sol–gel method at a relatively low temperature of 900 °C. The crystal structure examined by X-ray powder diffraction indicates that the samples were single phase and crystallize in a rhombohedral () structure with increase the Cd content. The Rietveld refinement of the structure shows that the substitution of La by Cd in the La site changes the structure parameters, such as MnO bond length and MnOMn angles. Magnetic measurements reveal that the magnetization of these compounds exhibit a ferromagnetic to paramagnetic transition with an increasing in the Curie temperature T_C when x increases from 0.1 to 0.5. The resistivity measurements reveal that the samples exhibit a metallic to semiconductor transition and the electrical temperature transition T_P present a similar trend of T_C, with increasing the Cd content.     

Recording of hydrogen evolution—a way for controlling the doping process of sodium alanate by ball milling

A simple equipment was developed which allows to monitor gas evolution or absorption occurring in the course of a ball milling process. The equipment has been applied to characterize via hydrogen evolution the reduction process of metal halides used as doping agents in the preparation of sodium alanate hydrogen storage materials. The gas flow curves resulting from the measurements (Fig. 2, Fig. 3 and Fig. 4) deliver useful informations concerning the rate, progress and completion of each of the involved reduction process, so that the stoichiometry of the underlying chemical reactions could be conceived or confirmed ( (3), (4), (5), (6) and (7)). In the preparation of sodium alanate hydrogen storage materials, the presented method can help to find out ball milling parameters necessary to produce an optimal catalytic activity of a dopant.     

Structure at abrupt copper–alumina interfaces: An ab initio study

The atomistic structure and the energetics of Cu(1 1 1)/-Al₂O₃(0 0 0 1) interfaces for two experimentally observed interface orientation relationships were investigated from first-principles by means of the mixed-basis pseudopotential method. In the first orientation relationship, the direction of Cu is parallel to the direction of -Al₂O₃, and in the second the Cu is rotated with respect to the -Al₂O₃ by 90° around the interface normal [0 0 0 1]. Numerous candidate systems were considered for each case, covering all high-symmetry interface configurations, and with either Al or O termination of the -Al₂O₃(0 0 0 1) surfaces. For each of the most stable interfaces, full relaxations of the positions of all atoms were performed. It is found that despite the different atomistic structures of the two interface types, their interface stabilities, in terms of the work of separation, and their local atomistic structures are similar.     

High strain rate superplasticity in an Al–Mg–Sc–Zr alloy subjected to simple thermomechanical processing

Superior superplastic ductility of 2300% was achieved at 520 °C and  s⁻¹ in an Al–5%Mg–0.2%Sc alloy produced by traditional chill casting followed by cold rolling with a total reduction of 80%.     

Temperature dependent neutron powder diffraction study of the Laves phase compound TbCo2

The structure, magnetization and magnetostriction of Laves phase compound TbCo₂ are investigated by temperature dependent high resolution neutron powder diffraction. The compound crystallizes in the cubic Laves phase C15 structure above its Curie temperature T_C and exhibits a rhombohedral distortion (space group ) below T_C. By an appropriate extrapolation of the temperature factor of Co atom above T_C, the Rietveld refinement of the neutron powder diffraction data of the rhombohedral structure converges satisfactorily and reveals that the moments of Co1(3b) and Co2(9e) are almost equal. Tb moment follows well the Brillouin function. The total magnetic moment of TbCo₂ is about 5.8μ_B/f.u., the anisotropic magnetostriction constant λ₁₁₁ is about 4.6 × 10⁻³ and the volume magnetostriction ω_s is about 8.7 × 10⁻³ at 14 K.     

Investigation of cation-deficient quaternary thiospinels: single crystal study of Ag1.4Cr1.47Sn2.53S8

Single crystals of the quaternary thiospinel Ag_1.41(1)Cr_1.47(5)Sn_2.52(5)S₈ have been obtained by heating stoichiometric mixtures of elemental metals and sulfur at 750 °C. Structural analysis by single crystal X-ray diffraction shows that the above phase crystallizes in the space group with a = 10.4142(3) Å (R₁ = 0.0156 and wR₂ = 0.0416). The Ag-deficiency has been confirmed by solving the structures of crystals prepared in different batches and was observed to vary slightly between crystals. Magnetic studies on a monophasic powder sample with a nominal composition of Ag_1.63CrSn₃S₈ indicates anti-ferromagnetic ordering at low temperature. The high temperature susceptibility leads to a magnetic moment of 3.45 B.M. suggesting that chromium exists predominantly in a trivalent state.     

Optical absorption and spectroscopic characteristics of Tm ions doped NaY(MoO4)2 crystal

The polarized absorption and emission spectra have been measured for the Tm³⁺ doped NaY(MoO₄)₂ crystal and spectral parameters have been estimated from the absorption data based on the Judd–Ofelt theory. The effective intensity parameters (t = 2, 4, 6) are 11.67 ×10⁻²⁰, 2.21 × 10⁻²⁰, 1.74 × 10⁻²⁰ cm², respectively. From the intensity parameters, the radiative transition probabilities, radiative lifetimes, branching ratios and the emission cross-section have been calculated. In comparison with other Tm³⁺ doped laser crystals, Tm³⁺:NaY(MoO₄)₂ crystal has potential as a promising laser crystal.