DC-bias and visible light effect on dielectric characteristics of La_(0.5)Cr_(0.5)TiO_(3+δ)

La_(0.5)Cr_(0.5)TiO_(3+δ) ceramic sample was prepared via traditional solid-state reaction route. Frequency and temperature dependence of dielectric permittivity were studied in the range of 10~2~ 10~6 Hz and of 77 ~360 K, respectively. It was observed that extraordinarily high low-frequency dielectric constants appeared at room temperature, and dielectric relaxation peaks shifted to higher temperature with increasing frequency. In the dc-bias studies, it was also found that the dielectric permittivity had obviously dc-bias dependence in low frequency, but independence as the frequency above 14 kHz. Interestingly, the dielectric characteristics of the sample had obvious light dependence at room temperature within the measured frequency range. The results demonstrate that visible light improves the dielectric properties of the ceramic by means of I–V and complex impedance analysis.     

Effect of CuO addition on the sintering temperature and microwave dielectric properties of CaSiO3– Al2O3 ceramics

CuO-doped CaSiO3–1 wt% Al2O3 ceramics were synthesized via a traditional solid-state reaction method, and their sintering behavior,microstructure and microwave dielectric properties were investigated. The results showed that appropriate CuO addition could accelerate the sintering process and assist the densification of CaSiO3–1 wt% Al2O3 ceramics, which could effectively lower the densification temperature from1250 1C to 1050 1C. However, the addition of CuO undermined the microwave dielectric properties. The optimal amount of CuO addition was found to be 0.8 wt%, and the derived CaSiO3–Al2O3ceramic sintered at 1100 1C presented good microwave dielectric properties of εr?7.27,Q f?16,850 GHz and τf? 39.53 ppm/1C, which is much better than those of pure CaSiO3 ceramic sintered at 1340oC(Q f?13,109 GHz).The chemical compatibility of the above ceramic with 30 Pd/70 Ag during the cofiring process has also been investigated, and the result showed that there was no chemical reaction between palladium–silver alloys and ceramics.& 2014 Chinese Materials Research Society. Production and hosting by Elsevier B.V. All rights reserved.     

Effect of B2O3 on the aqueous tape casting and microwave properties of Li2O–Nb2O5–TiO2 ceramics

The effect of B2O3 addition on the aqueous tape casting, sintering, microstructure and microwave dielectric properties of Li2O-Nb2O5-TiO2 ceramics has been investigated. The tape casting slurries exhibit a typical shear-thinning behavior without thixotropy, but the addition of B2O3 increases the viscosity of the slurries significantly. It was found that doping of B2O3 can decrease the tensile strength, strain to failure and density of the green tapes. The sintering temperature could be lowed down to 900℃ with the addition of 2 wt% B2O3 due to the liquid phase effect. No secondary phase is observed. The addition of B2O3 does not induce much degradation on the microwave dielectric properties. Optimum microwave dielectric properties of εr 67, Q×f 6560 GHz are obtained for Li2O-Nb2O5-TiO2 ceramics containing 2 wt% B2O3 sintered at 900 1C. It represents that the ceramics could be promising for multilayer low-temperature co-fired ceramics (LTCC) application.     

Mechanical and thermal properties of NpO2 using LSDAt U approach

The elastic constants,bulk modulus,shear modulus,Young’s modulus,Debye temperature,isobaric heat capacity and minimum thermal conductivity are estimated for NpO2 using plane-wave pseudopotential method within the local spin density approximation plus Hubbard U(LSDAtU) theory.The computed lattice constants are in good agreement with the available experimental results and then three independent elastic constants were computed by means of the stress–strain method.From the knowledge of the elastic constants,the values of Young’s modulus,Poisson,Debye temperature and minimum thermal conductivity are obtained and they are 218 GPa,0.288,453.5 K and0.99 Wm-1K-1,respectively.The obtained mechanical and thermal properties of NpO2 are in agreement with the previous experimental and theoretical data.Our investigations which are unobtainable from previous report can provide valuable reference in the future.     

Induced modi fi cations in the properties of Sr doped BiFeO3 multiferr oics

Multiferroics exhibit unique combination of ferroic properties,simultaneously.For instance,in BiFeO3,magnetic and electric properties co-exist.In this work,BiFeO3 and Sr-doped BiFeO3 samples with general formula,Bi1-x Srx FeO3(x=0.00,0.05,0.10,0.20,and 0.30) were synthesized by sol-gel auto-combustion technique,in order to investigate these ferroic properties.The samples were confrmed to have perovskite type rhombohedral structure,characteristic of BiFeO3.A dilute phase of Bi2Fe4O9was also found in all the Sr-doped samples.The micrographs of the palletized samples revealed that minutely doped Sr might not have any effect on the morphology of the samples.Frequency dependent dielectric measurements were carried out at room temperature for all the samples from 100 Hz to 1 MHz.The dielectric constant of un-doped sample at low frequency was 52 which decreased with increasing Sr doping.An enhancement of magnetic properties was observed with increasing the Sr contents.Pure BiFeO3 material was observed to have the least value of remanent magnetization.As the Sr2+ tions were doped in BiFeO3,its magnetization and remanence were increased to 0.867 emu/g and 0.175 emu/g,respectively,at x=0.30.     

Electroch emical properties and interfacial reactions of LiNi0.5Mn1.5O4-δ nanorods

LiNi0.5Mn1.5O4-δ which possesses a high voltage of 4.7 V vs.Li+/Li and stable structure has been considered as a promising cathode material for high energy Li-ion batteries.In this study,well-crystalli...     

Synthesis of dental resins using diatomite and nano-sized SiO2 and TiO2

The mechanical properties of dental composites were improved by porous diatomite and nano-sized silica (OX-50) used as co-fillers.The resin composites,filled with silanized OX-50 and silanized diatomit...     

A.C. conductivity and relaxation dynamics in zinc–borate glasses

The frequency-dependent dielectric dispersion of ZnO–Na2O–Al2O3–B2O3(in mol%) glass prepared by the melt quenching technique is investigated in the temperatur e ranges from room temperature to 420 K. Dielectric relaxation has been analyzed based on the behavior of electric modulus behavior. An analysis of the real and imaginary parts of dielectric is performed assuming the ideal Debye behavior as confirmed by Cole–Cole plot. The activation energy associated with the dielectric relaxation determined from the electric modulus spectra was found to be 1.863 eV, which is close to that the activation energy for d.c. conductivity (1.871 eV), indicating the similar nature of relaxation and conductivity.     

La2O3–Al2O3 –SiO2 glass-infiltrated 3Y-TZP all-ceramic composite for the dental restora tive application

The 3 mol% yttria stabilized tetragonal zirconia polycrystals (3Y-TZP) powder had three particle size distributions, while the fine one was lower than 100 nm. The 3Y-TZP compact was prepared by dry-pressing under pressures ranged from 10 to 30 MPa and then presintered at 1250°C for 2 h. The matrix dry-pressed under the pressure of 20 MPa had a porosity of 16.7% and could be easily processed by computer aided design and computer aided manufacturing (CAD/CAM), and which had been infiltrated by the La2O3–Al2O3–SiO2 glass at 1200°C for 4 h. The flexural strength and fracture toughness of the composite were 710.7 MPa and 6.51 MPa m^1/2, respectively. The low shrinkage (0.3%) of the composite can satisfy the net-shape fabrication standard. XRD results illustrated that zirconia in the La2O3–Al2O3–SiO2 glass-infiltrated 3Y-TZP all-ceramic composite was mainly in the tetragonal phase. SEM and EDS results indicated that the pores of the matrix were almost filled by the La2O3–Al2O3 –SiO2 glass     

Ti – Cu– Zr–Fe– Nb ultrafine structur e-dendrite composites with good mechanical properties and biocompat ibility

Ti-Cu-Zr-Fe-Nb ultrafine structure-dendrite composites were designed by inducing Nb and more Ti to a Ti-Cu-Zr-Fe glass-forming alloy composition and prepared by copper mold casting.The composite alloys consist of β-Ti dendrites and ultrafine-structured CuTi₂ and CuTi phases as well as a trace amount of glassy phase.The volume fraction of β-Ti dendrites increases with the increase in content of Nb which acted as the β-Ti phase stabilizer in the alloys.The composites exhibit high compressive yield strength exceeding1200 MPa,maximum strength around 1800 MPa and low Young’s modulus around 48 GPa.The plasticity of the alloys is strongly influenced by the volume fraction and morphology of the dendritic β-Ti phase,and the compressive plastic strain was enlarged from 5.9%for the 4 at%Nb alloy to 9.2%for the 8 at%Nb alloy.The preliminary cell culture experiment indicated good biocompatibility of the composite alloys free from highly toxic elements Ni and Be.These Ti-based composite alloys are promising to have potential structural and biomedical applications due to the combination of good mechanical properties and biocompatibility.     

Facile synthesis of nanosized sodium magnesium hydride, NaMgH3

The ternary magnesium hydride NaMgH 3 has been synthesised via reactive milling techniques.The method employed neither a reactive H2 atmosphere nor high pressure sintering or other post-treatment processes.The formation of the ternary hydride was studied as a function of milling time and ball:powder ratio.High purity NaMgH 3 powder(orthorhombic space group Pnma,a 5.437(2),b 7.705(5),c 5.477(2) ;Z 4) was prepared in 5 h at high ball:powder ratios and characterised by powder X-ray diffraction(PXD),Raman spectroscopy and scanning electron microscopy/energy dispersive X-ray spectroscopy(SEM/EDX).The products formed sub-micron scale(typically 200-400 nm in size) crystallites that were approximately isotropic in shape.The dehydrogenation behaviour of the ternary hydride was investigated by temperature programmed desorption(TPD).The nanostructured hydride releases hydrogen in two steps with an onset temperature for the first step of 513 K.     

Synthesis, structure, and optical properties of manganese phthalocyanine thin films and nanostructures

Manganese phthalocyanine(MnPc) nanostructures with different morphologies were prepared on porous anodic alumina oxide(AAO) at different substrate temperature(T_S=50 ℃,80 ℃,120 ℃,180 ℃,240 ℃) in an organic molecular beam deposition(OMBD) system.The nanostructures morphologies were studied using scanning electron microscopy(SEM) and the results showed that the nanostructures morphologies could be modulated by the control of T_S,as a result,the continuous film was obtained at 50 ℃,whereas the nanorods(NRs),nanoribbons(NBs),nanowires(NWs),nanosheets(NSs) and nanoparticles(NPs) were facilely generated as T_S increased.At the same time,the density and the uniformity of the nanostructures decreased.The results of X-ray diffraction(XRD) indicated that only the(3-phase polymorph formed throughout the growth process irrelevant to the T_S.Additionally,the ultraviolet visible(UV-Vis) absorption spectra demonstrated that the main absorption bands of MnPc nanostructures showed a remarkable band broadening as the T_S was increased.     

Grain size-dependent electrical resistivity of bulk nanocrystalline Gd metals

The electrical resistivity of the as-consolidated and coarse-grained bulk gadolinium(Gd) metals was studied in the temperature range of 3-315K.The experimental results showed that with decrease in the grain size of Gd grains from micrometer to nanometer range,the room temperature electrical resistivity increased from 209.7 to 333.0 μΩcm,while the electrical resistivity at the low temperature of 3K was found to increase surprisingly from 16.5 to 126.3 μΩcm.The room temperature coefficient resistivity(TCR) values were obtained as 39.2×10-3,5.51×10-3 and 33.7×10-3K-1.The ratios of room temperature to residual resistivity [RRR=ρ(300K)/ρ(3K)] are 2.64,11.0,respectively,for the as-consolidated samples at 280℃ and 700℃ with respect to that of the coarse-grained sample.All results indicate the remarkable influence of the nanostructure on the electrical resistivity of Gd due to the finite size effect and large fraction of grain boundaries.     

Microstructure, mechanical and thermo-physical properties of hot-pressed Al2O3-GdAlO3-ZrO2 ceramics with eutectic composition

A low cost chemical co-precipitation method was employed to fabricate nanoscale Al_2O_3-GdAlO_3-ZrO_2 powder with eutectic composition. A careful control of reaction conditions was required during the preparation. The synthesized nanopowders exhibited a particle size of 20-200 nm, and were highly dispersive and uniform. The results showed that calcination temperature had an important influence on the phase constituents of the nanopowders. With increasing the calcination temperature, a phase transformation from θ-Al_2O_3 to α-Al_2O_3 and a thermal decomposition from Gd_3 Al_5O_(12)(GdAG) to GdAlO_3 and α-Al_2O_3 occurred in sequence. A calcination temperature of 1300 ℃ was needed for the crystallization of α-Al_2 O_3. These nanosized powders were consolidated via hot pressing to produce a fully densified ceramic composite with eutectic composition. The Al_2O_3-GdAlO_3-ZrO_2 ceramic hot-pressed at 1500 ℃ exhibited a relative density of 99.4%, a flexural strength of 485 MPa and a fracture toughness of 6.5 MPa m~(1/2). The ceramic had a thermal conductivity of 1.9 W m K~(-1) at 1200 ℃ and a thermal expansion coefficient of 9.49 ×10~(-6) K~(-1) at 1100 ℃.     

Structural and dielectric study of nano-crystalline single phase Sn1−xNixS (xNi=0–10%) showing room temperature ferromagnetism

SnS is a promising Ⅳ-Ⅵ semiconductor,which is very less explored for diluted magnetic semiconducting and dielectric applications.In this study,the Ni doping(x_(Ni)=0-10mol%) effects on SnS host lattice were investigated.A simple and low cost co-precipitation technique was employed to grow Ni doped SnS powders.The X-ray diffraction confirmed single phase orthorhombic structure with a nano-crystalline nature that was further verified through the surface structure observed by scanning electron microscopy.Near edge x-ray absorption fine structure spectroscopy revealed a shift in the Ni absorption edge towards higher energy,depicting the formation of Ni~(+3) oxidation state.The impedance measurements,in the frequency range 1 kHz to 20 MHz,depict that owing to the excellent sensitivity to the electromagnetic radiations at the low energy,the Ni doped SnS finds potential applications in various energy related devices.Vibrating sample magnetometer measurements have elucidated room temperature ferromagnetism,which depicts potential memory device applications.     

Activated carbon derived from rice husk by NaOH activation and its application in supercapacitor

Four activated carbon(AC) samples prepared from rice husk under different activation temperatures have been characterized by N2adsorption–desorption isotherms, thermogravimetric analysis(TGA–DTA), Fourier transform infrared spectroscopy(FTIR) and scanning electron microscopy(SEM). The specific surface area of AC sample reached 2681 m2 g 1under activation temperature of 800 1C. The AC samples were then tested as electrode material; the specific capacitance of the as-prepared activated carbon electrode was found to be 172.3 F g 1using cyclic voltammetry at a scan rate of 5 mV s 1and 198.4 F g 1at current density 1000 mA g 1in the charge/discharge mode.& 2014 Chinese Materials Research Society. Production and hosting by Elsevier B.V. All rights reserved.     

Growth, structural, optical, thermal and dielectric properties of a novel semi-organic nonline ar optical crystal: Dichloro-diglycine zinc II

Dichloro-diglycine zinc II(DCDGZ II),a semi-organic nonlinear optical material has been synthesized and single crystals were grown from the aqueous solution up to dimensions 20×10×3 mm3.The title compound,DCDGZ II(C4H10Cl2N2O4Zn H2O) crystallizes into monoclinic structure with the space group of C2/c.The unit-cell parameters were found to be a=14.4191(7),b=6.9180(2),c=12.9452(6) and Z=4.In the crystal structure,DCDGZ II layer is building up alternatingly with layers of water in which the zinc ions lie on a twofold axis.Theoretical calculations for polarizability,which are useful for device fabrication were made using Clausius–Mosotti equation and Penn analysis and the results were compared.Fourier transform infrared(FTIR) spectroscopic studies were performed for the identification of the different functional groups presented in the compound.The UV–vis–NIR absorption spectrum reveals that the lower UV cut-off wavelength is 240 nm.The optical band gap of the crystal was estimated as 2.2 eV.The surface morphology,thermal behaviour,dielectric properties have been studied using SEM,TG/DTA and LCR HITESTER analyzer.The nonlinear optical property of the crystal was also confirmed using Kurtz powder technique.     

Effect of Co addition on crystallization and magnetic properties of FeSiBPCu alloy

The effects of Co addition on the microstructure,crystallization processes and soft magnetic properties of(Fe1 xCox)83Si4B8P4Cu1(x?0.35,0.5,0.65)alloys were investigated.The experimental results demonstrated that the addition of Co decreased the thermal stability against crystallization of the amorphous phase,and thus improved the heat treatment temperature of this alloy.Fe Co Si BPCu nanocrystalline alloys with a dispersedα0-Fe Co phase were obtained by appropriately annealing the as-quenched ribbons at 763 K for 10 min.Theα0-Fe Co with grains size ranging from 9 to 28 nm was identified in primary crystallization.The coercivity(Hc)markedly increased with increasing x and exhibited a minimum value at x0.35,while the saturation magnetic flux density(Bs)shows a slight decrease.The(Fe0.65Co0.35)83Si4B8P4Cu1nanocrystalline alloy exhibited a high saturation magnetic flux density Bsof 1.68 T,a low coercivity,Hcof 5.4 A/m and a high effective permeability meof 29,000 at 1 k Hz.     

Effect of pickling processes on the microstructure and properties of electroless Ni–P coating on Mg–7.5Li–2Zn–1Y alloy

The electroless plating Ni–P is prepared on the surface of Mg–7.5Li–2Zn–1Y alloys with different pickling processes.The microstructure and properties of Ni–P coating are investigated.The results show that the Ni–P coatings deposited using the different pickling processes have a different high phosphorus content amorphous Ni–P solid solution structure,and the Ni–P coatings exhibit higher hardness.There is higher phosphorus content of Ni–P amorphous coating using 125 g/L Cr O3and 110 ml/L HNO3(w68%)than using 180 g/L Cr O3and 1 g/L KF during pre-treatment,and the coating structure is more compact,and the Ni–P coatings exhibit more excellent adhesion with substrate(Fcup to22 N).The corrosion potential of Ni–P coating is improved and exhibits good corrosion resistance.As a result,Mg-7.5Li-2Zn-1Y alloy is remarkably protected by the Ni–P coating.     

Core loss analysis of Finemet type nanocrystalline alloy ribbon with different thickness

Nanocrystalline soft magnetic materials are widely used in power electronic applications due to their high permeability,magnetization and low core loss.In this paper,Fe_(73.5)Cu_1Nb_3Si_(15.5)B_7(at%)nanocrystalline alloy ribbons,with ultra-thin thickness of 14μm,and also 18 and 22μm,were prepared by a planar flow casting method with a single roller device.Soft magnetic properties of these ribbons were analyzed after nanocrystallization annealing.The experiments were conducted on toroidal samples using IWATSU B-H Analyzer over a frequency range of 10–100 kHz,at induction amplitudes of 100–500 m T,at room temperature.It was found that the excess eddy current loss P_(ex)was the dominant factor in the overall core loss above 10 k Hz.The toroidal samples made of the 14μm thickness ribbon exhibit very low total core loss of 48 W/kg at a frequency of100 kHz and magnetic flux density of 300 mT.The ratio of the P_(ex)was up to 89%at 100 kHz.The ribbon with lower thickness exhibits lower P_(ex)and therefore lower total core loss.The domain structure evidences were found.It indicates that the ribbons with small thickness are preferable for application in high frequency condition.