Structure and microwave dielectric characteristics of lithium-excess Ca0.6Nd0.8/3TiO3/(Li0.5Nd0.5)TiO3 ceramics

Compositions based on (1−x)Ca_0.6Nd_8/3TiO₃−x(Li_1/2Nd_1/2)TiO₃ + yLi (CNLNTx + yLi, x = 0.30–0.60, y = 0–0.05), suitable for microwave applications have been developed by systematically adding excess lithium in order to tune the microwave dielectric properties and lower sintering temperature. Addition of 0.03 excess-Li simultaneously reduced the sintering temperature and improved the relative density of sintered CNLNTx ceramics. The excess Li addition can compensate the evaporation of Li during sintering process and decrease the secondary phase content. The CNLNTx (x = 0.45) ceramics with 0.03 Li excess sintered at 1190 °C have single phase orthorhombic perovskite structure, together with the optimum combination of microwave dielectric properties of ɛ_r = 129, Q × f = 3600 GHz, τ_f = 38 ppm/°C. Obviously, excess-Li addition can efficiently decrease the sintering temperature and improve the microwave dielectric properties. The high permittivity and relatively low sintering temperatures of lithium-excess Ca_0.6Nd_0.8/3TiO₃/(Li_0.5Nd_0.5)TiO₃ ceramics are ideal for the development of low cost ultra-small dielectric loaded antenna.     

Fluorescence properties and relaxation processes of Tb3+ ions in ZnCl2-based glasses

60ZnCl₂–20KCl–20BaCl₂–xTbCl₃ glasses (x = 0.10, 0.25, 0.50, 0.75, 1.00, and 1.25) were prepared by melt-quenching method, and Tb³⁺ fluorescence properties were investigated under 355 nm excitation. Regardless of x values, the electrons that were relaxed from the ⁵D₃ to ⁵D₄ level of Tb³⁺ ions by the multiphonon relaxation, were repressed to 28% of all the excited electrons because the ZnCl₂-based glass had much lower phonon energy than oxide glasses. For 0 < x ≤ 0.34, the cross relaxation, (⁵D₃ → ⁵D₄) → (⁷F₀ ← ⁷F₆), was repressed, and consequently 72% and 28% of all the excited electrons were radiatively relaxed by the ⁵D₃ → ⁷F_J (J = 6, 5, 4, 3, and 2) and ⁵D₄ → ⁷F_J (J = 6, 5, 4, and 3) transitions, respectively. The lifetimes of the ⁵D₃ and ⁵D₄ initial levels were obtained to be 1.1 and 2.1 ms, respectively.     

Crystal structure and magnetic properties of Pr- and Ti-substituted La2RuO5

Polycrystalline samples of Pr- and Ti-substituted La₂RuO₅ were prepared applying a soft-chemistry route based on the thermal decomposition of citrate-stabilized precursors. The simultaneous substitution on the La-sites by Pr and on the Ru-sites by Ti results in samples of the composition La_2−xPr_xRu_1−yTi_yO₅ with 0 ≤ x ≤ 0.75 and 0 ≤ y ≤ 0.4. The crystal structures of these compounds were analyzed by Rietveld refinement of powder X-ray diffraction patterns. For pure La₂RuO₅ a structural transition from a monoclinic room-temperature modification to a triclinic low-temperature structure was found at 161 K. This structural change is linked to a low-temperature long-range ordered spin-singlet ground state formed by Ru⁴⁺ spin-moments. Both the structural transition and the formation of the singlet ground state become progressively suppressed with higher Ti contents, while the Pr substitution has only a minor influence on the dimerization. The behavior of the Curie–Weiss temperatures can be explained assuming two almost independent magnetic sublattices corresponding to the ruthenium and the rare-earth ions, respectively. For all investigated properties, i.e. crystal structure, magnetic susceptibilities, and dimerization temperature T_d, a completely additive behavior of the effects of Pr-substitution and Ti-substitution is observed.     

Effect of Fe and Co doping on electrical and thermal properties of La0.5Ce0.5Mn1−x(Fe,Co)xO3 manganites

The effect of Fe and Co doping on structural, electrical and thermal properties of half doped La_0.5Ce_0.5Mn_1−x(Fe, Co)_xO₃ is investigated. The structure of these crystallizes in to orthorhombically distorted perovskite structure. The electrical resistivity of La_0.5Ce_0.5MnO₃ exhibits metal-semiconductor transition (T_MS at ∼225 K). However, La_0.5Ce_0.5Mn_1−xTM_xO₃ (TM = Fe, Co; 0.0 ≤ x ≤ 0.1) manganites show semiconducting behavior. The thermopower measurements infer hole as charge carriers and electron–magnon as well spin wave fluctuation mechanism are effective at low temperature domain and SPC model fits the observed data at high temperature. The magnetic susceptibility measurement confirms a transition from paramagnetic to ferromagnetic phase. The observed peaks in the specific heat measurements, shifts to lower temperatures and becomes progressively broader with doping of transition metals on Mn-site. The thermal conductivity is measured in the temperature range of 10–350 K with a magnitude in between 10 and 80 mW/cm K.     

Room temperature multiferroic properties of (Bi0.95La0.05)(Fe0.97Mn0.03)O3/NiFe2O4 double layered thin film

(Bi_0.95La_0.05)(Fe_0.97Mn_0.03)O₃/NiFe₂O₄ double layered thin film was prepared on a Pt(111)/Ti/SiO₂/Si(100) substrate by a chemical solution deposition method. X-ray diffraction and Raman scattering spectroscopy studies confirmed the formation of the distorted rhombohedral perovskite and the inverse spinel cubic structures for the (Bi_0.95La_0.05)(Fe_0.97Mn_0.03)O₃/NiFe₂O₄ double layered thin film. The (Bi_0.95La_0.05)(Fe_0.97Mn_0.03)O₃/NiFe₂O₄ double layered thin film exhibited well saturated ferromagnetic (2 M_r of 18.1 emu/cm³ and 2H_c of 0.32 kOe at 20 kOe) and ferroelectric (2P_r of 60 μC/cm² and 2E_c of 813 kV/cm at 866 kV/cm) hysteresis loops with low order of leakage current density (4.5 × 10⁻⁶ A/cm² at an applied electric field of 100 kV/cm), which suggest the ferroelectric and ferromagnetic multi-layers applications in real devices.     

Hydrothermal synthesis of Sr–Ce–Sn–Mn–O mixed oxidic/stannate pyrochlore and its catalytic performance for NO reduction

Mixed oxides and pyrochlore-type materials based on the Sr, Ce, Sn, and Mn elements have been prepared by hydrothermal method using a mixture of nitrate salts at 200 °C for 40 h under N₂ atmosphere. Two groups of solids were synthesized: (i) (Sr_xCe_1?x)₂Sn₂O_7±δ (0.345 ≤ x ≤ 0.365) and (ii) (Sr_xCe_1?x)₂(Sn_yMn_1?y)₂O_7±δ (0.345 ≤ x ≤ 0.365, 0.385 ≤ y ≤ 0.395). The structure of the solids were studied by X-ray diffraction and the main crystal phases determined were SnO₂, (SrCe)₂Sn₂O₇ and a trace amount of CeO₂ in group (i) and only SnO₂ and CeO₂ were detected in group (ii). The mixed oxides/stannate pyrochlore have been tested as catalyst for NO reduction with hydrocarbons (CH₄, C₂H₄, and C₃H₆) in the presence of O₂. The CeO₂ containing stannate Sr_2xCe_2?2xSn₂O_7±δ pyrochlore coexist with SnO₂ (group (i)) was found to be the best for NO + C₃H₆ reaction giving very high N₂ production at 350 °C in the presence of O₂ and water vapor. SnO₂ as well as CeO₂ alone were also synthesized by the hydrothermal method and their NO reduction properties have been compared with those of the groups (i) and (ii).     

Highly porous ZnS microspheres for superior photoactivity after Au and Pt deposition and thermal treatment

This work highlights the enhanced photocatalytic activity of porous ZnS microspheres after Au and Pt deposition and heat treatment at 500 °C for 2 h. Microporous ZnS particles of size 2–5 μm with large surface area 173.14 m² g⁻¹ and pore volume 0.0212 cm³ g⁻¹ were prepared by refluxing under an alkaline medium. Photoluminescence of ZnS at 437 nm attributed to sulfur or zinc vacancies were quenched to 30% and 49%, respectively, after 1 wt% Au and Pt loading. SEM images revealed that each ZnS microparticle consist of several smaller ZnS spheres of size 2.13 nm as calculated by Scherrer's equation. The rate of photooxidation of 4-nitrophenol (10 μM) under UV (125 W Hg arc–10.4 mW/cm²) irradiation has been significantly improved by Au and Pt deposition followed by sintering due to better electron capturing capacity of deposited metals and growth of crystalline ZnS phase with less surface defects.     

Structural,optical and morphological properties of La,Cu co-doped SnO2 nanocrystals by co-precipitation method

Sn_0.96−xLa_0.04Cu_xO₂ (0 ⩽ x ⩽ 0.03) nanocrystals have been successfully synthesized by employing a simple co-precipitation method. The crystal structure of the synthesized nanocrystals was found to be tetragonal rutile of tin oxide by using X-ray diffraction technique and was not affected by doping. The change in lattice parameters was discussed based on the secondary phase formation and presence of Cu²⁺/Cu³⁺ in LaSnO₂ lattice. The variation in size and shape of the nanocrystals by Cu-doping was discussed using scanning electron microscope. The chemical stoichiometry of Sn, Cu, La and O was confirmed by energy dispersive X-ray spectra. The best optical transparency and lower absorption observed at Sn_0.97La_0.02Cu_0.01O₂ nanocrystals seems to be optimal for industrial applications especially as transparent electrode. The initial blue shift of energy gap from 3.65 eV (Cu = 0%) to 3.78 eV (Cu = 1%) (ΔE_g ≈ 0.13 eV) is due to the distortion in the crystal structure of the host compound and generation of defects. The red shift of energy gap after Cu = 1% is due to the charge-transfer transitions between the metal ions d-electrons and the SnO₂ conduction or valence band. Lattice mode of SnO₂ at 686 cm⁻¹ in Sn_0.98La_0.02O₂ nanocrystals and anti-symmetric SnOSn stretching mode of the surface bridging oxide around 634–642 cm⁻¹ in Cu doped Sn_0.98La_0.02O₂ nanocrystals was confirmed by Fourier transform infrared spectra.     

Luminescence properties of Sn2P2Se6 crystals

A large family of Sn_2yPb_2(1−y)P₂S_6xSe_6(1−x) semiconductor-ferroelectric crystals were obtained by the Bridgman technique. The photoluminescence properties of the Sn_2yPb_2(1−y)P₂S_6xSe_6(1−x) family crystals strongly depend on their chemical composition, excitation energy and temperature. The influence of the Pb → Sn and S → Se isovalent substitutions on the luminescence properties of a crystal with the Sn₂P₂Se₆ basic composition was investigated. A broad emission band observed in the Sn₂P₂Se₆ crystal with a maximum roughly at 600 nm (at T = 8.6 K) was assigned to a band-to-band electron-hole recombination, whereas broad emission bands, peaked near 785 nm (at T = 8.6 K) and 1025 nm (at T = 44 K) were assigned to an electron-hole recombination from defect levels localised within the bandgap. Possible types of recombination defect centres and specific mechanisms of luminescence in the Sn₂P₂Se₆ semiconductor-ferroelectric crystals were considered and discussed on the basis of the obtained results and the referenced data.     

Age hardening behaviors,mechanical and corrosion properties of deformed Mg–Mn–Sn sheets by pre-rolled treatment

The age behaviors, mechanical and corrosion properties of Mg–1.5Mn–xSn (x = 1 and 5 wt.%) alloys under three aging conditions have been investigated. The results reveal that both age behaviors and mechanical properties are improved with the increment of Sn. Meanwhile, the mechanical properties of EA (extrusion + artificial aging) state Mg–1.5Mn–5Sn alloy are higher than those of SA (solid solution + artificial aging) state sample, which are mostly attributed to fine grain and high density secondary precipitate. In addition, an accompanying improvement in age hardening response and strength is achieved in ERA (extruded + rolled + aging) state alloy compared with EA state one. The main reasons are related to the formations of a large number of dislocations and deformation twins, which provide effective nucleation sites to form fine β-Mg₂Sn strengthening precipitates during the following aging process. In addition, compared with EA state sample, a lower corrosion rate of ERA alloy is confirmed by Tafel curves and electrochemical impedance spectroscopy results, which is mainly related to the formation of a thick anodic passivation film on the surface.     

Microwave-polyol controlled synthesis and magnetic properties of monodisperse CoxNi1−xFe2O4/MWCNT nanocomposites

Monodisperse Co_xNi_1−xFe₂O₄ nanoparticles (x = 0, 0.2, 0.4, 0.5, 0.6, 0.8, and 1) with controllable composition attached on the multi-walled carbon nanotubes (MWCNTs) were prepared by microwave-polyol method. The composition of Co_xNi_1−xFe₂O₄ nanoparticles can be controlled through adjusting the atomic ratios of cobalt and nickel nitrate in the mixed solution. The influence of the microwave power and microwave irradiation time on the monodispersion of nanoparticles was also investigated. The results show quasi-spherical Co_xNi_1−xFe₂O₄ nanoparticles with the face-centered cubic structure and average crystallite size (6 nm) are uniformly dispersed on MWCNTs. The saturation magnetization of Co_xNi_1−xFe₂O₄/MWCNT nanocomposites increases gradually from 12.90 to 20.03 emu/g with increasing Co²⁺ concentration. The coercivity is almost zero at room temperature, which indicates the superparamagnetic behavior.     

Electro-magnetic transport behavior of La0.7Ca0.3MnO3/SnO2 composites

The composites of (1 ? x)La_0.7Ca_0.3MnO₃ (LCMO) + xSnO₂ (x = 0.01, 0.05, 0.10, 0.30, 0.50, 0.60, 0.65 and 0.70) were synthesized by conventional solid-state reaction method. The results of X-ray diffraction (XRD) and scanning electronic microscopy (SEM) indicate that SnO₂ and LCMO coexist in the composites and SnO₂ mainly segregates at the grain boundaries of LCMO, which are in accordance with the results of the magnetic measurements. The detailed electrical characterizations for all the samples showed that a new metal–insulator (M–I) transition temperature (T_P2) appeared at a lower temperature compared with the intrinsic metal–insulator (M–I) transition temperature (T_P1) when x < 0.50 (T_P1 > T_P2). When x > 0.50, T_P1 disappeared, leaving only T_P2. The resistivity percolation threshold of the composites occurred at x = 0.60. Corresponding to the two M–I transition peaks, the curves of magnetoresistance against temperature also showed two peaks for all composites. These phenomena can be explained by the segregation of a new phase related to SnO₂ at the grain boundaries or surfaces of the LCMO grains.     

Effects of Sn content on thermal stability and mechanical properties of the Ti60Zr10Ta15Si15 amorphous alloy for biomedical use

The (Ti₆₀Zr₁₀Ta₁₅Si₁₅)_100−xSn_x (x = 0, 4, 8, 12 at.%) amorphous ribbons were prepared by the single roll melt-spinning method, and the effects of the Sn content on the thermal stability, the elastic modulus and nanohardness of the Ni-free Ti-based alloys were investigated. It is found that Sn additions decrease the glass formation ability of the Ti₆₀Zr₁₀Ta₁₅Si₁₅ alloy. The content of Sn addition has an important impact on the elastic modulus and nanohardness of the alloys. The amorphous alloy with 4% Sn addition exhibits the highest the elastic modulus and nanohardness, which are 111 GPa and 7.0 GPa, respectively. The correlation between the mechanical properties and Sn content was discussed based on the free volume containing in the as-spun ribbons.     

Structure-dielectric properties relationships in copper-substituted magnesium ferrites

Nanocrystalline powders of copper-substituted magnesium ferrites with general formula Mg_1−xCu_xFe₂O₄ (x = 0.00, 0.17, 0.34, 0.50, 0.67, 0.84, 1.00) were prepared for the first time by sol–gel auto-combustion method, using glycine as fuel agent. Solid phase chemical reactions and the occurrence of spinel structure were monitored by using infrared spectroscopy. X-ray diffraction analysis confirmed the spinel single-phase formation. A shift from cubic structure to tetragonal structure starting with x = 0.84 was also observed. Microstructure of the samples was analyzed by scanning electron microscopy and particle size was estimated from the micrographs.Analysis of dielectric properties revealed very low values of dielectric loss at frequencies over 10 MHz.     

Pt nanoparticles modified by rare earth oxides: Electronic effect and influence to catalytic hydrogenation of 3-phenoxybenzaldehyde

The rare earth elements (La, Ce, Nd, Sm, Pr, and Gd) modified Pt/Al₂O₃ catalysts were prepared by the colloidal deposition and chemical reduction methods, respectively. Pt nanoparticles with average size 3 ± 0.5 nm were uniformly dispersed on the surface of Al₂O₃ for the samples prepared by the colloidal deposition method, which exhibited higher activities in the hydrogenation of 3-phenoxybenzadehyde than the corresponding samples prepared by chemical reduction method. Moreover, except Gd, the catalysts modified by rare earth elements showed better catalytic performance than unmodified Pt/Al₂O₃. For Pt–Ce/Al₂O₃ catalyst, when the weight percent of Pt and Ce was 0.5 and 0.25, respectively, the hydrogenation conversion of 3-phenoxybenzaldehyde was 97.3% after 6 h reaction. This activity improvement is due to the electronic interaction between Pt and rare earth elements, which was investigated by X-ray photoelectron spectroscopy.     

Influence of Ga3+ ions on spectroscopic and dielectric features of multi component lithium lead boro bismuth silicate glasses doped with manganese ions

Multi-component glasses of the chemical composition 19.5Li₂O–20PbO–20B₂O₃–30SiO–(10 − x)Bi₂O₃–0.5MnO:xGa₂O₃ with 0 ≤ x ≤ 5.0 have been synthesized. Spectroscopic (optical absorption, IR, Raman and ESR) and dielectric properties were investigated. Optical absorption and ESR spectral studies have indicated that managanese ions do exist in Mn³⁺ state in addition to Mn²⁺ state in the samples containing low concentration of Ga₂O₃. The IR and Raman studies indicated increasing degree of disorder in the glass network with the concentration of Ga₂O₃ up to 3.0 mol%. The dielectric constant, loss and ac conductivity are observed to increase with the concentration of Ga₂O₃ up to 3.0 mol%. The quantitative analysis of the results of dielectric properties has indicated an increase in the insulating strength of the glasses as the concentration of Ga₂O₃ is raised beyond 3.0 mol%. This has been attributed to adaption of gallium ions from octahedral to tetrahedral coordination.     

Effects of TiO2 nanoparticles addition on microstructure,microhardness and tensile properties of Sn–3.0Ag–0.5Cu–xTiO2 composite solder

The effects of TiO₂ nanoparticles addition on the microstructure, microhardness, and tensile properties of Sn–3.0 wt.%Ag–0.5 wt.%Cu–x wt.%TiO₂ (x = 0, 0.05, 0.1, and 0.6) composite solders were systematically investigated. Scanning electron microscope (SEM) was used to observe the microstructural evolution of the composite solders, measure the size of the Ag₃Sn grains, and estimate the spacing between the Ag₃Sn grains in the solder matrix. Energy-dispersive X-ray spectroscopy (EDX) and X-ray diffractometry (XRD) were used to identify the phases of eutectic areas in the composite solder matrix. Results show that both the average size of Ag₃Sn grains and the spacing between the Ag₃Sn grains decrease significantly, which might owe to the strong adsorption effect and high surface free energy of the TiO₂ nanoparticles. The microhardness is improved by 37% compared with TiO₂-free noncomposite solder as the weight percentage of TiO₂ nanoparticles is 0.1 wt.%. The improvement is due to the microstructural change of the composite solders, which is in good agreement with the prediction of the classic theory of dispersion strengthening. Tensile tests reveal that the TiO₂-containg composite solder alloys have higher ultimate tensile strength (UTS) than TiO₂-free noncomposite solder alloy due to solid solution hardening. UTS of solder alloys have a logarithmic increase relation with strain rate ranging from 10⁻³ s⁻¹ to 10⁻¹ s⁻¹ and decreases with an increase of test temperatures ranging from 25 °C to 125 °C.     

The AMWCNTs supported porous nanocarbon composites for high-performance supercapacitor

The porous nanocarbons supported by acid-treated multiwall carbon nanotubes (PC@ACNTs) were prepared by the combination of the hydrothermal polymerization of glucose on ACNTs, carbonization under N₂ protection and final activation with ZnCl₂. The materials were characterized by transmission electron microscopy, X-ray powder diffraction and Raman spectra. The results indicated that the ACNTs distributed uniformly into the framework of the porous carbon. The composites showed the high BET specific surface area up to 1712 m² g⁻¹ and good conductivity. The electrochemical measurements indicated that the composites processed good performances for electrochemical energy storage (210 F g⁻¹ at 0.5 A g⁻¹), and high stability (>99.9%), much higher than the corresponding ACNTs, porous carbons and the samples prepared by using raw MWCNTs as source. The good performance of PC@ACNTs composites was relative with the synergy of good conductivity of ACNTs and large specific surface areas of PC.     

Microstructural,electrical and optical properties of indium tin oxide (ITO) nanoparticles synthesized by co-precipitation method

In the present study, the synthesis of Tin doped indium oxide (ITO) nanopowder at different compositions (In/Sn = 0, 5, 10, 15 at %) was carried out by co-precipitation method. The decomposition of precipitated indium tin acetylacetonate precursor to form In₂O₃–SnO₂ (Sn_1?xIn_xO₂) at 400 °C was confirmed by the thermal and FTIR studies. The changes in strain and grain size of the synthesized particle with respect to dopant concentration were determined from the X-ray diffraction (XRD) analysis. Transmission electron microscopy (TEM) images support to confirm the grain size. The optical properties on ITO nanoparticles were analyzed with UV–visible spectroscopy, and band gap was found to vary from 3.62 to 3.89 eV with Sn dopant concentration. This variation was ascribed to the quantum confinement effect.     

Effect of polymer modifier chain length on thermal conductive property of polyamide 6/graphene nanocomposites

The influence of polymer modifier chain length on the thermal conductivity of polyamide 6/graphene (GA) nanocomposites, including through-plane (λ_z) and in-plane (λ_x) directions were investigated. Here, three chain lengths of double amino-terminated polyethylene glycol (NH₂–PEG–NH₂) were used to covalently functionalize graphene with graphene content of 5.0 wt%. Results showed that λ_z was enhanced with the chain length of NH₂–PEG–NH₂ increased, but λ_x reached a maximum value at a certain chain length of NH₂–PEG–NH₂. The maximum λ_z and λ_x of GA are 0.406 W m⁻¹ K⁻¹ and 9.710 W m⁻¹ K⁻¹, respectively. This study serves as a foundation for further research on the thermal conductive property of graphene nanocomposites using different chain lengths of polymer modifier to improve the λ_z and λ_x of the thermal conductive materials.