Effect of Th doping on superconductivity in CePt3Si

Alloys from the solid solution Ce_1−xTh_xPt₃Si (x = 0.0, 0.02, 0.04, 0.08, 0.1, 0.2 and 1.0) were prepared by arc-melting. X-ray Rietveld powder analyses revealed that alloys in the compositional range 0 ≤ x ≤ 0.2 crystallize with the CePt₃B-type with a random distribution of Ce and Th atoms in positions 1(b) (1/2, 1/2, z) of the noncentrosymmetric space group P4mm. Th-doping results in a rapid suppression of the superconductivity. The alloy with x = 0.02 shows the onset of superconducting state at T_c = 400 mK, while that with x = 0.04 remains in normal metallic state at least down to 70 mK.     

Hydrophilicity and photocatalysis of Ti1−xVxO2 films prepared by sol-gel method

Ti_1−xV_xO₂ films were prepared by sol-gel dip-coating method. To study the effects of vanadium incorporation on the self-cleaning properties of TiO₂ film, the crystallization behavior and surface morphology of Ti_1−xV_xO₂ films were investigated by an X-ray diffraction (XRD) analysis and an Atomic force microscope (AFM) respectively. The band-gap E_g of Ti_1−xV_xO₂ was determined by optical transmission spectra. Hydrophilicity and photocatalysis of Ti_1−xV_xO₂ films were characterized. The results showed that Ti_1−xV_xO₂ films had super-hydrophilicity and greater photocatalysis under day light illumination when x = 0.1-0.2. An optimal photocatalytic activity was obtained when x = 0.15. Moreover, Ti_0.85V_0.15O₂ films were proven to have excellent photocatalysis and hydrophilicity in visible region simultaneously, which made the application of Ti_0.85V_0.15O₂ film as self-cleaning and anti-fogging material practical under everyday condition.     

Cerium concentration and temperature dependence of the luminescence of Lu2Si2O7:Ce scintillator

The crystals of (Lu_1−xCe_x)₂Si₂O₇ (LPS) (x = 0.003, 0.005, 0.0075, 0.01 and 0.013) are grown by Czochralski (Cz) method. The scintillation and optical properties of these LPS:Ce crystals were studied and compared systematically, mainly focused on the absorption, photoluminescence (PL) and photoluminescence excitation (PLE) and decay time. It is found that the self absorption of LPS:Ce is increased as the cerium doping concentration increases; the PLE curves of LPS:Ce samples are influenced by the both cerium doping concentrations and sample thickness. Specially, thicker and higher cerium doped LPS:Ce, i.e. the stronger self absorption, will lead to incomplete PLE curves. The temperature dependence of luminescence of LPS:0.3%Ce, including the decay time, PLE and PL properties, is investigated.     

Piezoelectric and dielectric properties of Dy2O3-doped (Bi0.5Na0.5)0.94Ba0.06TiO3 lead-free ceramics

(Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ + x wt% Dy₂O₃ with x = 0-0.3 ceramics were synthesized by conventional solid-state processes. The effects of Dy₂O₃ on the microstructure, the piezoelectric and dielectric properties were investigated. X-ray diffraction pattern confirmed that the coexistence of tetragonal and rhombohedral phases in the (Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ composition was not changed by adding 0.05-0.3 wt% Dy₂O₃. SEM images indicate that all the ceramics have pore-free microstructures with high density, and that doping of Dy₂O₃ inhibits the grain growth of the ceramics. The addition of Dy₂O₃ shows the double effects on decreasing the piezoelectric and dielectric properties for 0 < x < 0.15 when Dy³⁺ ions substitute B-site Ti⁴⁺ ions, and increasing the properties for 0.15 < x < 0.3 when Dy³⁺ ions enters into A-site of the perovskite structure. The optimum electric properties of piezoelectric constant d₃₃ = 170 pC/N and the dielectric constant ?_r = 1900 (at a frequency of 1 kHz) are obtained at x = 0.3.     

Hydrogen storage characteristics of nanocrystalline and amorphous Mg2Ni-type alloys prepared by melt spinning

In order to improve the hydrogen storage characteristics of the Mg₂Ni-type alloys, Ni in the alloy is partially substituted by element Mn, and melt-spinning technology is used for the preparation of the Mg₂Ni_1−xMn_x (x = 0, 0.1, 0.2, 0.3, 0.4) hydrogen storage alloys. The microstructures of the as-cast and spun alloys are characterized by XRD, SEM and HRTEM. The hydrogen absorption and desorption kinetics of the alloys are measured by an automatically controlled Sieverts apparatus. The electrochemical performances are tested by an automatic galvanostatic system. The results show that the as-spun Mn-free alloy holds typical nanocrystalline structure, whereas the as-spun alloys containing Mn displays a nanocrystalline and amorphous structure. The hydrogen absorption and desorption capacities and kinetics of the alloys increase with rising spinning rate. Additionally, melt spinning markedly improves the electrochemical hydrogen storage capacity and cycle stability of the alloys containing Mn. With an increase in the spinning rate from 0 (As-casts is defined as spinning rate of 0 m/s) to 30 m/s, the discharge capacity of the (x = 0.3) alloy mounts up from 92.3 to 211.1 mAh/g, and its capacity retaining rate at 20th charging and discharging cycle grows from 36.21% to 76.02%.     

Hydrogen insertion effect on the magnetic properties of Ce2Pd2In

The effect of hydrogenation on the crystal structure and the magnetic properties of Ce₂Pd₂InH_x was studied up to the hydrogen content x = 4. In the entire range of x, the system retains the tetragonal unit cell of the parent compound, and nearly isotropic expansion of the crystal lattice was observed for x ≤ 2.5. Below x ≈ 1.5, the hydrides exhibit ferromagnetic properties, while at larger hydrogen content antiferromagnetic behaviour was found in samples with the composition up to x ≈ 2.5. In the entire Ce₂Pd₂InH_x series the magnetic behaviour is governed by the well-localized magnetic moments carried by trivalent cerium ions with fairly stable 4f¹ electronic configuration.     

An investigation on hydrogen storage kinetics of nanocrystalline and amorphous Mg2Ni1−xCox (x = 0-0.4) alloy prepared by melt spinning

In order to improve the hydrogen storage kinetics of the Mg₂Ni-type alloys, Ni in the alloy was partially substituted by element Co, and melt-spinning technology was used for the preparation of the Mg₂Ni_1−xCo_x (x = 0, 0.1, 0.2, 0.3, 0.4) hydrogen storage alloys. The structures of the as-cast and spun alloys are characterized by XRD, SEM and TEM. The hydrogen absorption and desorption kinetics of the alloys were measured by an automatically controlled Sieverts apparatus. The electrochemical hydrogen storage kinetics of the as-spun alloys is tested by an automatic galvanostatic system. The hydrogen diffusion coefficients in the alloys are calculated by virtue of potential-step method. The electrochemical impedance spectrums (EIS) and the Tafel polarization curves are plotted by an electrochemical workstation. The results show that the substitution of Co for Ni notably enhances the glass forming ability of the Mg₂Ni-type alloy. Furthermore, the substitution of Co for Ni, instead of changing major phase Mg₂Ni, leads to forming secondary phases MgCo₂ and Mg. Both the melt spinning treatment and Co substitution significantly improve the hydrogen absorption and desorption kinetics. The high rate discharge ability, the hydrogen diffusion coefficient and the limiting current density of the alloys significantly increase with raising both the spinning rate and the amount of Co substitution.     

Dielectric properties and crystal structure of La(Mg1/2Ti1/2)O3 ceramics with Mg substituted by Co

Solid solutions of (1 − x)La(Co_1/2Ti_1/2)O₃-xLa(Mg_1/2Ti_1/2)O₃ were used to prepare La(Mg_1−xCo_x)_1/2Ti_1/2O₃ using solid-state synthesis. X-ray diffraction patterns of the sintered samples revealed single phase formation. A maximum density of 6.01 g/cm³ was obtained for La(Mg_1−xCo_x)_1/2Ti_1/2O₃ (x = 1) ceramics sintered at 1375 °C for 4 h. The maximum values of the dielectric constant (?_r = 29.13) and the quality factor (Q × f = 80,000 GHz) were obtained for La(Mg_1−xCo_x)_1/2Ti_1/2O₃ with 1 wt% ZnO additive sintered at 1375 °C for 4 h. The temperature coefficient of resonant frequency τ_f was −59 ppm/°C for x = 0.3.     

Fabrication and properties of Ba(Zr1−xCex)0.9Y0.1O2.95/NaCl composite electrolyte materials

Ba(Zr_1−xCe_x)_0.9Y_0.1O_2.95/NaCl (x = 0.1, 0.2 and 0.3) composite electrolyte materials were fabricated with ZnO as sintering aid. The effect of ZnO on the properties of Ba(Zr_1−xCe_x)_0.9Y_0.1O_2.95 matrix were investigated. The phase composition and microstructure of samples were characterized by XRD and SEM, respectively. The electrochemical performances were studied by three-probe conductivity measurement and AC impedance spectroscopy. XRD results showed that Ba(Zr_1−xCe_x)_0.9Y_0.1O_2.95 with 2 mol% of ZnO was perovskite structure. The relative density of this sample was above 95% when sintered at 1450 °C for 6 h. By adding 10 mol% of NaCl to Ba(Zr_1−xCe_x)_0.9Y_0.1O_2.95 with 2 mol% of ZnO that was sintered at 1400 °C for 6 h, the conductivity was increased. The electrical conductivity of 1.26 × 10⁻² S/cm and activation energy of 0.23 eV were obtained when tested at 800 °C in wet hydrogen.     

Characterization of the martensitic transformation in Ni50−xTi50Cux alloys through pure thermal measurements

The addition of a third element to the Ni-Ti system often changes the product and the path of the martensitic transformation of the alloy, which is a direct B2-B19′ transformation for the NiTi alloy in the fully annealed state. In this study we investigate the martensitic transformation of fully annealed Ni_50−xTi₅₀Cu_x (x = 3-10 at%) shape memory alloy (SMA) samples using differential scanning calorimetry (DSC) and the four-probe electrical resistance (ER) measurements under stress-free conditions. DSC and ER data show that the ternary alloy goes through a direct B2-B19′ transformation for Cu content between 3 and 7 at% and through the two-stage B2-B19-B19′ transformation for Cu content between 8 and 10 at%. We find good agreement between the two techniques as regards the detection of the phase transformation temperatures. B19′ starting and finishing temperatures decreases with the increases of Cu content and show a significant reduction starting from 7 at%; the range of temperatures in which B19 is stable increases with increasing Cu content.     

Electrochemical hydrogen storage properties of non-stoichiometric La0.7Mg0.3−xCaxNi2.8Co0.5 (x = 0-0.10) electrode alloys

The microstructure and electrochemical hydrogen storage characteristics of La_0.7Mg_0.3−xCa_xNi_2.8Co_0.5 (x = 0, 0.05 and 0.10) alloys prepared by arc-melting and subsequent powder sintering method are investigated. The electrochemical measurement results show that the cycle stability after 100 charge/discharge cycles first increases from 46.4% (x = 0) to 54.3% (x = 0.05), then decreases to 43.2% (x = 0.10), and the high rate dischargeability increases from 64.5% (x = 0) to 68.5% (x = 0.10) at the discharge current density of 1200 mA/g. The electrochemical impedance spectroscopy analysis indicates that the electrochemical kinetics of the alloy electrodes is improved by increasing Ca. The entire results exhibit that a suitable content of Ca (x = 0.05) can improve the overall electrochemical hydrogen storage characteristics of the alloys.     

V-Ni-Ti multi-phase alloy membranes for hydrogen purification

Hydrogen-selective membranes formed from body centred cubic alloys can exhibit very high hydrogen permeability, but are prone to brittle failure due to excessive hydrogen absorption. Until issues associated with this are overcome, these materials will not provide a viable alternative to Pd-based membranes. Multi-phase V-Ni-Ti alloys which contain a significant proportion of a BCC component show promise for this application. In order to examine this system in greater detail, alloys of the general form V_85−xTi_xNi₁₅, in which x was varied between 0 and 30 (at.%), were fabricated via arc melting and electrical-discharge wire cutting. Hydrogen permeation measurements of Pd-coated samples at 400 °C showed a monotonic increase in permeability with increasing Ti, reaching a maximum of 1.0 × 10⁻⁷ mol H₂ m⁻¹ s⁻¹ Pa^−0.5 for the V₅₅Ti₃₀Ni₁₅ alloy at 400 °C. The driving force for hydrogen transport is provided by hydrogen absorption, which varies non-linearly with Ti content, and is dependent on the volume fraction of BCC phase, and levels of Ti and Ni solution in the BCC phase. Diffusion coefficients of atomic H through the bulk alloys alloys are dependent largely on microstructure. Whereas the V₈₅Ni₁₅ alloy forms a single phase microstructure, progressive substitution of V with Ti introduced several minor phases; a NiTi-type phase (formed when x ≥ 5), and a NiTi₂-type phase (formed when x ≥ 10), both as V-containing solid solutions. These minor phases act as barriers to hydrogen diffusion, resulting in a significantly reduced diffusion coefficient compared to single-phase BCC alloys. Importantly, the mechanical stability of these alloys appears to be enhanced by the multi-phase microstructure. These alloys therefore show great promise for meeting future flux, cost and durability targets.     

Influence of the C14 Ti35.4V32.3Fe32.3 Laves phase on the hydrogenation properties of the body-centered cubic compound Ti24.5V59.3Fe16.2

Bcc Ti_24.5V_59.3Fe_16.2 alloys containing 10 and 30% of C14 Laves phase inclusions were prepared by induction melting followed by annealing at 1000 °C. X-ray powder diffraction and BSE microscopy confirmed the presence of the C14 Laves phase (average composition Ti_35.4V_32.3Fe_32.3) embedded in the bcc matrix. The two end members of the series, the C14 Laves phase and the bcc Ti_24.5V_59.3Fe_16.2 alloy, have very different hydrogenation behaviors. The C14 Laves phase does not absorb as much hydrogen as does the bcc phase. No equilibrium plateau and little hysteresis between absorption and desorption were observed at 25 °C for the C14 Laves on the PCI curves whereas those of the bcc sample present one equilibrium plateau and significant hysteresis between absorption and desorption. As a result, the absorption capacity and the length of the equilibrium plateau of the multiphase alloys decrease with the C14 Laves phase content. The hydrogenation properties of an as-cast bcc Ti_24.5V_59.3Fe_16.2 sample were also investigated: the kinetics of the first hydrogenation is found to be slower and the plateau pressures higher for the as-cast alloy than for the annealed sample.     

Influence of the addition of vanadium on the hydrogenation properties of the compounds TiFe0.9Vx and TiFe0.8Mn0.1Vx (x = 0, 0.05 and 0.1)

TiFe_0.9 and TiFe_0.8Mn_0.1 hydrides have suitable equilibrium pressures at ambient conditions and are potential candidates for hydrogen storage applications. In this work, we study the influence of the addition of small amounts of vanadium on the hydrogenation properties of TiFe_0.9V_x and TiFe_0.8Mn_0.1V_x (x = 0, 0.05 and 0.1) alloys. The excess of Ti from TiFe in these materials results in the precipitation of Ti and Ti₂Fe-type phases. In the analysis of the chemical composition, vanadium was observed in small amount in all phases for each sample which contains vanadium. Vanadium tends to substitute Fe sites, which results in a decrease of the plateau pressures. The addition of vanadium as TiFe_0.8Mn_0.1V_x (x = 0.05 and 0.1) alloys has beneficial effects on the equilibrium plateaus of the hydrides: the plateaus become flatter and a significant reduction in the pressure hysteresis is observed.     

Luminescent properties of UV excitable blue emitting phosphors MSr4(BO3)3:Ce (M = Li and Na)

A series of Ce³⁺ doped novel borate phosphors MSr₄(BO₃)₃ (M = Li or Na) were successfully synthesized by traditional solid-state reaction. The crystal structures and the phase purities of samples were characterized by powder X-ray diffraction. The optimal concentrations of dopant Ce³⁺ ions in compound MSr₄(BO₃)₃ (M = Li or Na) were determined through the measurements of photoluminescence spectra of phosphors. Ce³⁺ doped phosphors MSr₄(BO₃)₃ (M = Li or Na) show strong broad band absorption in UV spectral region and bright blue emission under the excitation of 345 nm light. In addition, the temperature dependences of emission spectra of M_1+xSr_4−2xCe_x(BO₃)₃ (M = Li or Na) phosphors with optimal composition x = 0.05 for Li and x = 0.09 for Na excited under 355 nm pulse laser were also investigated. The experimental results indicate that the M_1+xSr_4−2xCe_x(BO₃)₃ (M = Li or Na) phosphors are promising blue emitting phosphors pumped by UV light.     

Improving the piezoelectric thermal stability by tailoring phase transition behavior in the new (1 − x)[0.65PbMg1/3Nb2/3O3-0.35PbTiO3]-xBiZn1/2Ti1/2O3 perovskite solid solutions

The phase transition behavior and its effect on thermal stability of the piezoelectric properties of the (1 − x)[0.65PbMg_1/3Nb_2/3O₃-0.35PbTiO₃]-xBiZn_1/2Ti_1/2O₃ ceramics with 0 ≤ x ≤ 0.06 were investigated. The phase transition from the monoclinic to tetragonal phase was determined by the dielectric constant and elastic constant measurements. The temperature independent piezoelectric response with −d₃₁ = 188 pC/N was obtained from 175 to 337 K for the composition with x = 0.02. The enhanced thermal stability of piezoelectric response was achieved by shifting the monoclinic-tetragonal phase transition to the lower temperature.     

Effect of Ce on microstructure, mechanical properties and corrosion behavior of high-pressure die-cast Mg-4Al-based alloy

Mg-4Al-xCe-0.3Mn (x = 0, 1, 2, 4 and 6 wt.%) alloys were prepared by high-pressure die-casting. The microstructures, mechanical properties and corrosion behavior were investigated. The cross-section of test bar is divided into the fine skin region and the relatively coarse interior region by a narrow band. The dendritic arm spacing is greatly reduced and the secondary phases Al₁₁Ce₃ and (Al, Mg)₂Ce with the former being the dominant one substitute the Mg₁₇Al₁₂ phase with addition of Ce. When Ce content reaches 4 wt.%, the alloy exhibits an optimal cost performance ratio. The improved mechanical properties maintained up to 200 °C are mainly related to the fine grain size and the main strengthening phase Al₁₁Ce₃, which is present in a high volume fraction, and possesses fine acicular morphology and relatively good thermal stability. The improved corrosion resistance is attributed to the microstructure modification of the alloys and the corrosion product films.     

DC magnetization investigations in Ti1−xMnxO2 nanocrystalline powder

In the present paper, DC magnetization investigation on the insulating nanocrystalline powder samples of Ti_1−xMn_xO₂ (x = 0, 0.05, 0.10, and 0.15) prepared by simple chemical route is reported. Structural measurements revealed phase pure anatase structure of TiO₂ when x ≤ 0.05 and a mixture of anatase and rutile TiO₂ along with the signature of Mn₃O₄ phase for x > 0.05. Magnetic measurements exhibited the presence of ferromagnetic ordering at room temperature in samples having either small fraction of Mn or no Mn at all. This ferromagnetic signature is accompanied with paramagnetic contribution which is found to dominate with increase in Mn concentration. The Ti_1−xMn_xO₂ sample having highest Mn concentration of x = 0.15 showed nearly paramagnetic behavior. However, at low temperatures, additional ferrimagnetic ordering arising due to Mn₃O₄ (T_C = 42 K) is evidenced in the doped samples. Consistent with the XRD investigations, the isofield DC-magnetization measurements under field cooled and zero field cooled (FC-ZFC) histories corroborated the presence of Mn₃O₄ phase. Also, distinct thermomagnetic irreversibility has been observed above 42 K. These results are suggestive of presence of weak ferromagnetic ordering possibly due to defects related with oxygen vacancies.     

Gaseous and electrochemical hydrogen storage kinetics of nanocrystalline Mg2Ni-type alloy prepared by rapid quenching

The nanocrystalline Mg₂Ni-type Mg₂Ni_1−xCu_x (x = 0, 0.1, 0.2, 0.3, 0.4) alloys were synthesized by direct melt quenching technique. The structures of the as-cast and quenched alloys were investigated by XRD, SEM and HRTEM. The gaseous hydrogen storage kinetics of the alloys was measured using an automatically controlled Sieverts apparatus. The electrochemical hydrogen storage kinetics of the alloys was tested by using constant current to charge and discharge the electrode. The results indicate that the substitution of Cu notably rendered the grain refinement of the as-cast alloys without altering the major phase Mg₂Ni. All the as-quenched alloys exhibit a nanocrystalline structure without the presence of any amorphous phase. It is found that the substitution of Cu for Ni and rapid quenching significantly ameliorated the gaseous and electrochemical hydrogen storage kinetics of the nanocrystalline Mg₂Ni_1−xCu_x (x = 0-0.4) alloys. Furthermore, both the rapid quenching treatment and the Cu substitution results in a notable increase in the hydrogen diffusion coefficient (D) as well as the limiting current density (I_L) but an obvious decline in the electrochemical impedance.     

Phase evolution, crystal structure and dielectric behavior of (1 − x)Nd(Zn0.5Ti0.5)O3 + xBi(Zn0.5Ti0.5)O3 compound ceramics

The phase evolution, crystal structure and dielectric properties of (1 − x)Nd(Zn_0.5Ti_0.5)O₃ + xBi(Zn_0.5Ti_0.5)O₃ compound ceramics (0 ≤ x ≤ 1.0, abbreviated as (1 − x)NZT-xBZT hereafter) were investigated. A pure perovskite phase was formed in the composition range of 0 ≤ x ≤ 0.05. The B-site Zn²⁺/Ti⁴⁺ 1:1 long range ordering (LRO) structure was detected by both XRD and Raman spectra in x ≤ 0.05 samples. However, this LRO structure became gradually degraded with an increase in x. The dielectric behaviors of the compound ceramic at various frequencies were investigated and correlated to its chemical composition and crystal structure. A gradually compensated τ_f value was obtained in (1 − x)NZT-xBZT microwave dielectrics at x = 0.03, which was mainly due to the dilution of dielectric constant in terms of Claussius-Mossotti differential equation.