Slater–Pauling behavior and half-metallicity in Heusler alloys Mn2CuZ (Z = Ge and Sb)

The Slater–Pauling behavior and half-metallic properties of full-Heusler alloys Mn₂CuZ (Z = Ge and Sb) have been studied by first-principles calculations. It is found that the total spin moment (M_t) and the number of valence electrons (Z_t) follow a Slater–Pauling rule of M_t = Z_t ? 28 rather than M_t = Z_t ? 24 in normal Heusler alloys. Mn₂CuSb is predicted to be a half-metal at equilibrium lattice constant and Mn₂CuGe is also half-metallic with a small expansion of the lattice. Mn₂CuGe and Mn₂CuSb are both ferrimagnets with total spin moment of +0.97μ_B/f.u. and +2.00μ_B/f.u., respectively. Considering Mn₂CuGe and Mn₂CuSb have 29 and 30 valence electrons, the S-P curve of M_t = Z_t ? 28 works quite well. This different S-P rule is strongly related to the low-lying Cu states and the weak hybridization between the d states of Cu and Mn.     

Agglomeration of urinary nanocrystallites: Key factor to formation of urinary stones

With transmission electron microscopy (TEM) and nanoparticle size analyzer, comparative studies were conducted on the property variation of nanocrystallites in the urine of 5 lithogenic patients and 5 healthy subjects following the placement time (t₁). These properties include average particle size (d?), size distribution, intensity–autocorrelation function, Zeta potential (ζ) and aggregation state. With the prolongation of t₁ from 0 h to 4 h, d? value of the nanocrystallites in urine of lithogenic patients increased from 742 nm to 1667 nm, the autocorrelation time increased from 7.68 ms to 1050 ms and ζ decreased from ?1.52 mV to ?4.44 mV, respectively; the autocorrelation curves were of fluctuating and unsmooth, and TEM showed that most of the patient's urinary nanocrystallites were in aggregation state and three types of agglomeration were observed. However, for nanocrystallites in urine of healthy subjects, there was little variation in the above properties within 4 h. The autocorrelation curves were of regular and smooth, and TEM showed that healthy urinary nanocrystallites were well-dispersed. The above results show that the nanocrystallites in urine of healthy subjects can keep stability, whereas those of lithogenic patients are easier to agglomerate gradually; and the agglomeration of urinary nanocrystallites is the key factor to stone formation.     

Structural and optical analyses of polycrystalline Zn1−xSbxSe thin films prepared by resistive heating technique

Here we report the influence of Sb doping on the structural and optical properties of Zn_1−xSb_xSe (0 ⩽ x ⩾ 0.15) thin films prepared by thermal evaporation technique on glass substrate. Various characterization techniques such as X-ray diffraction (XRD), EDS, Raman spectroscopy and spectroscopic ellipsometer are employed to assess the structural and optical properties of the deposited films. XRD analysis reveals the formation of polycrystalline cubic structure having preferred growth orientation along (1 1 1) plane without any evidence of secondary phases. Crystallographic parameters like grain size, micro strain, dislocation density, number of crystallites per unit area and texture coefficient point out the structural modification in ZnSe films with Sb inclusion. Raman analysis shows the existence of three 1LO, 2LO and 3LO phonon modes at 251, 511 and 745 cm⁻¹ in pure ZnSe while 3LO mode disappears by the incorporation of Sb atoms in ZnSe matrix. Increase in FWHM of Raman peaks with Sb concentration also indicates the change in crystalline quality of ZnSe films which is in accordance with our XRD results. Spectroscopic ellipsometry results demonstrate a decreasing trend for the optical band gap energy (from 2.61 eV to 1.81 eV) with increasing Sb content.     

Coupled substitutions in In2O3: New transparent conductors In2−xM2x/3Sbx/3O3 (M = Cu,Zn)

Two solid solutions In_2−xM_2x/3Sb_x/3O₃ (M = Cu, Zn) with the bixbyite structure have been synthesized in air at 1300 °C. The homogeneity range is larger for Zn (x = 0.42) than for Cu (x = 0.20) and the cationic distribution of the Cu/Sb and Zn/Sb couples is weakly ordered. These new oxides appear to be transparent conductors. Even fully deprived of tin, they have good potential properties. These oxides are either semiconductors with a small band gap (Cu/Sb) or semimetals (Zn/Sb) with σ = 3 × 10² (Ω cm)⁻¹ at room temperature. These materials are more efficient than bulk ITO prepared under the same experimental conditions, i.e. without reducing treatment (σ = 50 (Ω cm)⁻¹).     

Enhanced densification and microwave dielectric properties of Mg2TiO4 ceramics added with CeO2 nanoparticles

We report the study of the effects of processing parameters and additive concentration on the structure, microstructure and microwave dielectric properties of MTO–CeO₂ (x wt.%) ceramics with x = 0, 0.5, 1.0 and 1.5 prepared by solid-state reaction method by adding CeO₂ nanoparticles as a sintering aid. The pure Mg₂TiO₄ ceramics were not densifiable below 1450 °C. However, when CeO₂ nanoparticles were added to MTO, the densification achieved at 1300 °C along with the increase in average grain size with the uniform microstructure and improved microwave dielectric properties. This is mainly driven by the large surface energy of CeO₂ nanoparticles and their defect energy during the sintering process. While the addition of CeO₂ nanoparticles in MTO ceramics does not change the dielectric constant (?_r), the unloaded quality factor (Q_u) was altered significantly. MTO–CeO₂ (1.5 wt.%) ceramics sintered at 1300 °C exhibit superior microwave dielectric properties (?_r ～ 14.6, Q × f₀ ～ 167 THz), as compared to the pure Mg₂TiO₄ ceramics. The observed results are correlated to the enhancement in density and the development of uniform microstructure with the enhanced grain size.     

Basic zinc carbonate as a precursor in the solvothermal synthesis of nano-zinc oxide

ZnO nanoparticles were synthesized solvothermally in various diols (ethylene glycol, di(ethylene glycol), tetra(ethylene glycol), 1,2-propanediol, 1,4-butanediol), using basic zinc carbonate (2ZnCO₃·3Zn(OH)₂) as a precursor for the first time. Since ZnCO₃ was sparingly soluble in diols the transformation reaction proceeded at a low reaction rate. Ethylene glycol was found as the most suitable medium among five diols studied yielding the smallest ZnO particles (~ 55 nm) and short reaction time, t_r (2 h). Diols with shorter chain length produced smaller ZnO particles. p-Toluene sulfonic acid (p-TSA) acted as a catalyst and reduced t_r from 8 h to 2 h in concentration of 0.02 M. Optimum reaction conditions for the synthesis in ethylene glycol were 185 °C and 2 h. At higher p-TSA concentrations (0.04–0.08 M) the size of ZnO particles was reduced from 500–800 nm to 50–100 nm and crystallite size to 25–30 nm. Benzene sulfonic acid (BSA) and inorganic bases (LiOH, NaOH, and KOH) also showed catalytic activities. Raman and photoluminescence spectroscopies revealed high concentration of defects on ZnO surface causing the emission of visible light and giving this type of ZnO higher potential in various (opto)-electronic application in comparison to Zn(II) acetate based ZnO.     

Ag nanoparticles enhanced near-IR emission from Er3+ ions doped glasses

Vitreous materials containing rare-earth (RE) ions and metallic nanoparticles (NPs) attract considerable interest because the presence of the NPs may lead to an intensification of luminescence. In this work, the characteristics of 1.54 μm luminescence for the Er³⁺ ions doped bismuthate glasses containing Ag NPs were studied under 980 nm excitation. The surface plasmon resonance (SPR) band of Ag NPs appears from 500 to 1500 nm. Transmission electron microscopic (TEM) image reveals that the Ag NPs are dispersed homogeneously with the size from 2 to 7 nm. The strength parameters Ω_t(t = 2, 4, 6), spontaneous emission probability (A), radiative lifetime (τ) and stimulated emission section (σ_em) of Er³⁺ ions were calculated by the Judd–Ofelt theory. When the glass contains 0.2 wt% AgCl, the 1.54 μm fluorescence intensity of Er³⁺ reaches a maximum value, which is 7.2 times higher than that of glass without Ag NPs. The Ag NPs embedded glasses show significantly fluorescence enhancement of Er³⁺ ions by local field enhancement from SPR.     

Hydrothermal synthesis and 121Sb Mössbauer characterization of perovskite-type oxides: Ba2SbLnO6 (Ln = Pr,Nd, Sm,Eu)

A mild hydrothermal process to prepare Ba₂SbLnO₆ (Ln = Pr, Nd, Sm, Eu) perovskite-type oxides are presented. These perovskites were characterized on the basis of X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), inductively-coupled plasma spectra (ICP) techniques. Primary structure was confirmed using Rietveld method based on XRD data shows that the likely space groups of Ba₂SbLnO₆ are R-3 for Ln = Pr and Nd and F_m-3_m for Ln = Sm and Eu, respectively. The measurement of Mössbauer effect of the 37.2 keV γ transition of ¹²¹Sb indicates that the isomer shift of these perovskites falls in the region of the Sb⁵⁺ and reflects some hybridized-orbital behavior in Sb–O bonds.     

Study on dynamic strain aging phenomenon of 3004 aluminum alloy

3004 Aluminum alloy has been subjected to tension test at a range of strain rates (5.56 × 10⁻⁵ to 5.56 × 10⁻³ s⁻¹) and temperatures (233–573 K) to investigate the effect of temperature and strain rate on its mechanical properties. The serrated flow phenomenon is associated with dynamic strain aging (DSA) and yield a negative strain rate dependence of the flow stress. In the serrated yielding temperature region a critical transition temperature, T_t, was found. The critical plastic strain for the onset of serrations has a negative or positive temperature coefficient within the temperature region lower or higher than T_t. According to the activation energy, it is believed that the process at the temperature region lower than T_t is controlled by the interaction between Mg solute atom atmosphere and the moving dislocation. In the positive coefficient region, however, the aggregation of Mg atoms and precipitation of second phase decrease the effective amount of Mg atoms in solid solution and lead to the appearance of a positive temperature coefficient of the critical plastic strain for the onset of serrations.     

Doping effects of Li–Sb content on the structure and electrical properties of [(Na0.5K0.5)1 − x(Li)x(Sb)x(Nb)1 − xO3] lead-free piezoelectric ceramics

Ceramic samples of [Na_0.5K_0.5]_1 ? x(Li)_x(Sb)_x(Nb)_1 ? xO₃ (NKNLS) (x = 0.04–0.06) were prepared by high temperature solid-state reaction method. X-ray diffraction analysis of the powder samples suggests the formation of a single-phase material with transformation from orthorhombic to tetragonal crystal structure with increase in Sb content. Dielectric studies show a diffuse phase transition about 100 °C and another phase ferroelectric–paraelectric transition at 330 °C. Polarization vs. electric field (P–E) hysteresis studies show maximum remanent polarization (Pr ～ 0.66 C m^?2) for composition x = 0.05. AC conductivity in the compound increases with increase in temperature which may be attributed due to oxygen vacancies and show negative temperature coefficient of resistance (NTCR) effect.     

Ionic conductivity of high-purity Gd-doped ceria solid solutions

The Ce_1−xGd_xO_2−δ (0.02 ≤ x ≤ 0.3) solid solutions with ∼30 ppm SiO₂ were prepared through the conventional mixed-oxide method from high-purity CeO₂ and Gd₂O₃ powders. The ionic conductivity (especially the grain boundary (GB) conduction) in this system was studied as a function of dopant content, over the temperature range of 250–750 °C in air, using an impedance spectroscopy. The GB impedance played an important role in the total conduction in the samples with low Gd content (usually x ≤ 0.1), but decreased sharply with increasing Gd content. Both the total and GB conductivities maximized at the composition x = 0.15, and this composition also had the lowest activation energies for the total and GB conduction. The maximum total conductivity at 700 °C, σ_t = 4.07 (Ω m)⁻¹ with the activation energy, E_t = 0.77 eV, was found for the composition x = 0.15.     

Effect of Ni on reactive diffusion between Au and Sn at solid-state temperatures

Influence of Ni on the kinetics of the reactive diffusion between Au and Sn was experimentally studied at solid-state temperatures. Binary Sn–Ni alloys with Ni concentrations of 1, 3 and 5 mass% were used to prepare sandwich (Sn–Ni)/Au/(Sn–Ni) diffusion couples by a diffusion bonding technique. The diffusion couples were isothermally annealed at temperatures of T = 433, 453 and 473 K for various times in an oil bath with silicone oil. After annealing, AuNiSn₈, AuSn₄, AuSn₂ and AuSn compound layers were observed to form at the (Sn–Ni)/Au interface in the diffusion couple. The total thickness l of the compound layers monotonically increases with increasing annealing time t according to the equation l = k(t/t₀)ⁿ, where t₀ is unit time, 1 s. The exponent takes values between n = 0.29 and 0.37 under the present annealing conditions. Such values of n < 0.5 indicate that the grain boundary diffusion contributes to the rate-controlling process and the grain growth occurs at certain rates. The higher the Ni concentration of the Sn–Ni alloy is, the faster the overall growth of the compound layers occurs. This means that Ni is an accelerator for the reactive diffusion between Au and Sn at solid-state temperatures. The acceleration effect of Ni becomes more remarkable at higher annealing temperatures. Such influence of Ni on the kinetics is mainly attributed to the dependencies of the growth rate of the AuNiSn₈ layer on the composition of the Sn–Ni alloy and the annealing temperature.     

Thermal stability and photoluminescence of Zr1−xCexO2 (0 ≤ x ≤ 1) nanoparticles synthesized in a non-aqueous process

Complete range Zr_1−xCe_xO₂ (0 ≤ x ≤ 1) nanoparticles are synthesized by the thermal decomposition of metal-organic precursors (zirconium acetylacetonate and cerium acetylacetonate) in oleylamine. XRD and HRTEM indicate that all of the as-prepared nanoparticles are single-crystal, and the crystallinity becomes better with increasing Ce content. The Zr_1−xCe_xO₂ nanoparticles with Ce content larger than 1/8 crystallize in cubic fluorite phase. XRD measurements on the as-prepared and calcinated ZrO₂ samples reveal that the tetragonal ZrO₂ nanoparticles are stable below 600 °C, and the lattice parameters of ZrO₂ nanoparticles decrease with decreasing particle size. The thermal stability of the cubic phase increases with increasing Ce content. The UV–vis absorption spectra reveal that the band gap energy increases with increasing cerium content. Room-temperature photoluminescence (PL) spectra of pure ZrO₂ nanoparticles show strong emission peaks centered at about 441 nm at room temperature, which is attributed to the ionized oxygen vacancies in the nanoparticles. On the other hand, room-temperature PL spectra of the as-prepared CeO₂ nanoparticles shows two peaks at 417 and 436 nm, which might arise from the transition from the cerium 4f and to the oxygen 2p band (valence band) in CeO₂ and the presence of oxygen vacancies, respectively.     

Characterization of hot-pressed short ZrO2 fiber toughened ZrB2-based ultra-high temperature ceramics

Two different ZrB₂-based ultra-high temperature ceramics were produced by hot pressing: ZrB₂ + 20 vol.% SiC particle + 15 vol.% ZrO₂ fiber and ZrB₂ + 20 vol.% SiC whisker + 15 vol.% ZrO₂ fiber. The microstructures were analyzed by using transmission electron microscopy and high-resolution transmission electron microscopy. It was shown that a clean interface without any impurities was identified in ZrB₂-based hybrid ceramics with SiC whiskers and ZrO₂ fibers, which would significantly improve the toughening mechanism. The results of high-resolution transmission electron microscopy showed that stacking faults in SiC whiskers resulted from an insertion of a (111) layer, which would be one of the main reasons for material anisotropy. However, the interface between the SiC particle and ZrO₂ fiber was found to be ambiguous in ZrB₂-based hybrid ceramics with SiC particles and ZrO₂ fibers due to the slight reaction. The orientation relationship between t-ZrO₂ and m-ZrO₂ phases obeyed the classical correspondence: (100)_m//{100}_t and [001]_m//〈001〉_t, which further verified the feasibility of phase transformation toughening mechanism.     

The simulation of the electrochemical cathodic Ca–P deposition process

Electrochemical cathodic deposition has been widely employed for fabrication of Ca–P films onto surface of titanium. However, systematical and theoretical analyses for this process are rarely reported. In this study, a model of Ca–P nucleation for electrochemical deposition process was proposed based on classical crystallization theories of thermodynamics and kinetics. The obtained results from this model referred to that: the following results are obtained: the Ca–P phase precipitated on titanium is DCPD under lower loading current (I₀ < 0.5 mA) and shorter loading time (t < 50 s); the preferential precipitated phase on titanium is OCP under higher loading current (I₀ > 0.5 mA) and longer loading time (t > 50 s). Inspiringly, this theoretical model was successfully validated with our experimental results analyzed through high-resolution TEM micrographs.     

Decolorization of beads-milled TiO2 nanoparticles suspension in an organic solvent

In this paper, a new method is proposed for the decolorization of a yellow-hued suspension of rutile TiO₂ nanoparticles in an organic solvent (diethylene glycol dimethylether). The presence of color has always been undesirable in a suspension of nanoparticles filler used for industrial needs, particularly for optical applications.A colorless suspension was achieved by irradiating well-dispersed TiO₂ nanoparticles in an organic solvent with UV-light (λ = 254 nm) for 5 h. TiO₂ nanoparticles of 1 and 5 wt.% were dispersed using a beads mill method. Trimethoxytrifluor(propyl) silane was used as a dispersant to achieve stability. The effect of the UV-light irradiation on the TiO₂ nanosuspension was investigated by means of a Fourier transform nuclear magnetic resonance analyzer (FT-NMR). The dispersant was partially desorbed due to the interaction of UV light and the TiO₂/dispersant complex. Thus, an enhanced transparency and the absence of color were obtained for well-dispersed TiO₂ nanoparticles in an organic solvent.     

Mg–Zn–Y alloys with long-period stacking ordered structure: In vitro assessments of biodegradation behavior

Using Dulbecco's modified eagle medium (DMEM) with 10% fetal bovine serum (FBS) as simulated body fluid, degradation behavior of Mg_100 ? 3x(Zn₁Y₂)_x (1 ≤ x ≤ 3) alloy series with long period stacking order (LPSO) structures was investigated. As indicated, with increasing the volume fraction of LPSO phase, degradation rate of the alloys is accelerated. Further refining the grain size by microalloying with zirconium and warm extrusion has a significant effect to mitigate the degradation rate of the Mg₉₇Zn₁Y₂ alloy. Time-dependent behavior during degradation of the magnesium alloys can be described using an exponential decay function of W_R = exp(a + bt + ct²), where W_R is normalized residual mass/volume of the alloy. A parameter named as degradation half-life period (t_0.5) is suggested to quantitatively assess the degradation rate. For the localized-corrosion controlled alloys, the t_0.5 parameter physically scales with electrochemical response ΔE which is a range between corrosion potential (E_corr) and pitting potential (E_pt). In comparison with conventional engineering magnesium alloys such as the AZ31, WE43, ZK60 and ZX60 alloys, extruded Mg_96.83Zn₁Y₂Zr_0.17 alloy with LPSO structure exhibits a good combination of high mechanical strength, lower biodegradation rate and good biocompatibility.     

Magnetic properties for the transition-metal aluminides XAl2 (X = V,Cr, Mn,and Co): A first-principles study

We have investigated the magnetic properties of the transition-metal aluminides XAl₂ (X = V, Cr, Mn, and Co) in the MoSi₂ type structure by first-principles calculations. Considering the electron–electron correlations, we predict VAl₂ and CoAl₂ to be half-metallic ferromagnets. The transition-metal aluminides alloys, such as (CrFe)_0.5Al₂ and (MnFe)_0.5Al₂, obtained by substitution of half of the transition-metal atoms by other transition-metal atoms are nearly half-metals with high spin polarizations at the Fermi level. The density of states of these materials exhibit the features of a spin-up gap or a spin-down gap at the Fermi level. The total magnetic moments for these half-metals are integers and obey the Slater–Pauling rule of scaling linearly with the total number of the valence electrons in the unit cell in the form of M_t = N_t ? 28 (or M_t = 28 ? N_t). CrAl₂ and MnAl₂ are antiferromagnets, but their ferromagnetic spin configurations also show half-metallicity.     

Nanoparticles synthesis of tungsten disulfide via AOT-based microemulsions

The tungsten disulfide (WS₂) nanoparticles (most probably inorganic fullerene (IF)) with a narrow size distribution were synthesized by a reverse micelle technique for the first time. The particle size was controlled by varying water-to-surfactant molar ratio (W₀), aging time and reagent concentration. The synthesized WS₂ nanoparticles were characterized by zetasizer, UV–visible spectrophotometers and transmission electron microscopy (TEM). The WS₂ nanoparticles with particle diameter size of 7–12 nm were obtained via 24 h aging time. The particle size was controlled by changing the aging time and molar ratio of water/surfactant. Doubling W₀ increased the amount and particle size of WS₂ by 22 and 26%, respectively. The effect of aging time in the range of 6–24 h was investigated and the complete disappearance of yellowish color at 24 h resulted in an optically clear solution, which was the indication of WS₂ formation with 100% conversion of reactant ((NH₄)₂WS₄) in the batch reactor.     

Study of the properties of polymers obtained from vegetable oil derivatives by light scattering techniques

Polymers from oleic acid (principal fatty acid of the olive oil) and methyl oleate were studied by static (SLS) and dynamic (DLS) light scattering in acetone solution. The oleic acid (OA) and methyl oleate (MO) were first epoxidized using a performic acid generated in situ. The epoxidized oleic acid (EOA) and methyl oleate (EMO) were reacted with cis-1,2-cyclohexanedicarboxylic anhydride (CH) as cure agent, triethylamine (TEA) as initiator and small amount of 1,4-butanediol diglycidyl ether (BDGE). According to light scattering results the EMO products without BDGE present low M_W, however the EOA ones are characterized by aggregation and M_W approximately 1.98 × 10⁵ g/mol. The aggregation is evidenced by the presence of two modes in DLS experiments. The dimension of the single particle is approximately R_h = 5 nm and for the aggregates R_h increases until 169 nm. The samples with addition of BDGE in the reaction mixtures for both derivatives (EMO and EOA) result to macromolecular products with M_W higher than 1.71 × 10⁵ g/mol, however no aggregation of this macromolecules is observed. Both products present relatively small dimensions and random coil conformation behavior.