Relaxation mechanism analysis of synthetic fused quartz glass investigated by electrical impedance spectra

The synthetic fused quartz glasses with bare metal impurities have been analyzed by temperature- dependent electrical impedance spectroscopy. The complex electric impedance and the overlapping of the normalized dielectric modulus imply the single mechanism of dielectric and conduction relaxation in the fused quartz glass. Besides, the dependence of conductivity on temperature may attribute to the predominant electric relaxation to the delocalized or long range electronic hopping between the nonbridged dangling oxygen.     

Structural, electrical, dielectric and magnetic properties of Mn-Nd substituted CoFeO3 nano sized multiferroics

A series of Mn x Co_(1-x) Fe_(1-y) Nd_yO_3(where x=0.0–1.0 y=0.0–0.1) multiferroic nanocrystals was synthesized via sol-gel auto-combustion technique. The structure was confirmed by X-ray diffraction(XRD)while morphology was investigated by scanning electron microscopy(SEM). The electrical resistivity was observed to increase from 2.14 * 10~7 to 8.77 * 10~9 Ω-cm and activation energy was found to increase from 0.64 to 0.75 e V, while the drift mobility decreased from 4.75 * 10~(-13) to 1.27 * 10~(-15)cm~2V~(-1)S~(-1) by the substitution of Mn and Nd contents. The dielectric constant, dielectric loss and dielectric loss factor decrease with frequency and Mn-Nd contents. The saturation magnetization was increased from 34 to 70 emu g~(-1) while the coercivity decreased from 705 to 262 Oe with the increase of substituents.The increase in electrical resistivity and saturation magnetization while decrease in dielectric parameters and coercivity make these nanomaterials suitable for applications in microwave devices and longitudinal magnetic recording media.     

Fabrication of SrFe12-xNixO19 nanoparticles and investigation on their structural,magnetic and dielectric properties

SrFe12?xNixO19 nanoparticles (x = 0–1) were synthesized by a combustion sol–gel method. Their structure, dielectric and magnetic properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), an LCR metry, and vibrating sample mag-netometry (VSM).The results reveal that all samples of Ni doped compounds (SrFe12?xNixO19) withx < 0.2 are single phase. It appears that the Fe3+ions are substituted by Ni2+ ions on the crystallographic sites of the SrFe12O19 structure; however, forx≥ 0.2, the secondary Ni phase ferrite (NiFe2O3) appears, which reduces the saturation magnetization and coercivity. In addition, Ni doping reduces the dielectric con-stant, dielectric loss, and alternating current (ac) electrical conductivity of the samples. The variation in ac conductivity (σac) with frequency shows that the electrical conductivity in these ferrites is mainly attributed to the electron hopping mechanism.Therefore; all the single-phase Ni doped samples are suitable for use in magnetic recording media and microwave devices.     

Influence of Te doping on the dielectric and optical properties of InBi crystals grown by directional freezing

Stoichiometric pure and tellurium (Te) doped indium bismuthide (InBi) were grown using the directional freezing technique in a fabricated furnace. The X-ray diffraction profiles identified the crystallinity and phase composition. The surface topographical features were observed by scanning electron microscopy and atomic force microscopy. The energy dispersive analysis by X-rays was performed to identify the atomic proportion of elements. Studies on the temperature dependence of dielectric constant (?), loss tangent (tanδ), and AC conductivity (σ_ac) reveal the existence of a ferroelectric phase transition in the doped material at 403 K. When InBi is doped with tellurium (4.04 at%), a band gap of 0.20 eV can be achieved, and this is confirmed using Fourier transform infrared studies. The results thus show the conversion of semimetallic InBi to a semiconductor with the optical properties suitable for use in infrared detectors.     

Size-manipulat ion, compacti on and electrical properties of barium manganite nanorods synthesized via the CHM method

A composite-hydroxide mediated method was employed to synthesize barium manganite nanorods.Diameter,surface smoothness and uniformity of these nanorods were optimized by varying reaction temperature and reaction time.The rods with an average diameter of 200 nm and length of1–1.5 μm were obtained at optimum conditions of 200 1C/48 h.The dielectric study of these rods reveals that they have higher value of dielectric constant at lower frequencies which was attributed to the interfacial and rotational type polarizations.Similarly,the increase in dielectric constant with temperature was attributed to the thermal activation of such polarizations.Furthermore,the analysis of ln(J) vs.E1/2characteristics in the temperature range of 300–400 K shows that possible operative conduction mechanism was of Poole–Frenkel type.The value of βexp was found to be 4.85 times greater than the expected theoretical value of feld lowering coeffcient with an internal feld enhancement factor ofα2 23.5.This high value of βexp may be due to some localized electric felds existing inside the sample.     

Structural and dielectric properties of doped ferrite nanomaterials suitable for microwave and biomedical applications

The sol–gel auto-combustion method was adopted to synthesize nanomaterials of single-phase X-type hexagonal ferrites with the composition of Sr2?xGdxNi2Fe28?yCdyO46 (x=0.00, 0.02, 0.04, 0.06, 0.08, 0.10 and y=0, 0.1, 0.2, 0.3, 0.4, 0.5). The structural properties were carried out by XRD analysis and the lattice parameters show variation with the doping of Gd–Cd. The average particle size measured by TEM was in the range of 8–10 nm which is beneficial in obtaining suitable signal-to-noise ratio in recording media and biomedical applications. The room temperature resistivity enhanced with the increase of the dopant concentration. The increase in resistivity indicates that the synthesized materials can be considered good for the formation of the multilayer chip inductors (MLCIs) as well as for the reduction of eddy current losses. The dielectric constant decreased with the increase in the frequency which is the general reported trend of the hexagonal ferrites and can be explained on the basis of Koop?s theory and Maxwell–Wagner polarization-model. The abnormal dielectric behavior indicates the formation of small polarons in the material. The maximum value of tangent loss at low frequencies reflects the application of these materials in medium frequency devices (MF).     

Improvements of dielectric properties of Cu doped LaTiO_(3+δ)

The ceramic composites of Cu-doped La_(1-x )Cu_x TiO_(3+δ)(x=0.05, 0.15, 0.3, 0.5) were synthesized by conventional solid-state reaction. The complex dielectric properties of the composites were investigated as a function of temperature(77 K ≤T≤ 320 K) and frequency(100 Hz ≤ f ≤1 MHz) separately. In all composites, the dielectric constants increase monotonously and the dielectric loss undulates with temperature. And it is clearly observed that extraordinarily high low-frequency dielectric constant(～10~4)appear at room temperature in La_0.5Cu_0.5TiO_(3+δ), which is 100 times larger than that of La_0.95Cu_0.05 TiO_(3+δ). Interestingly, the dielectric constants increase remarkably with the doped Cu contents, meanwhile the dielectric loss for all samples is ideal lower than 1 at room temperature in the measured frequency range. By means of complex impedance analysis, the improvements of dielectric properties are attributed to both bulk contribution and grain boundary effect, in which the bulk polaronic relaxation and the Maxwell–Wagner relaxation due to grain boundary response are heightened remarkably with the high doped Cu contents.     

Laser-induced self-organization in Se–Te–Sn–Cd glassy semiconductor for developing novel light-sensing dielectrics

The laser-induced effects on dielectric properties of chalcogenide glass(Ch Gs) have been present in a glassy system of Se–Te–Sn–Cd for possible applications in optics and optoelectronics such as light-controlled capacitance-based touch displays. The temperature/frequency dependence of dielectric relaxation before and after laser exposure was investigated by using laser sources of different wavelengths(405 nm, 532 nm, 690 nm, and 785 nm). The result showed the presence of laser-induced residual effects on dielectric properties(dielectric constant/loss and a.c. conductivity) after the exposure of continuous-wave laser sources of chosen wavelengths.Further analysis indicates that the modification in the meta-stable state due to self-organization is the feasible mechanism of observed persistent light-sensing effects.     

Effects of MgO and TiO<Subscript>2</Subscript> on the viscous behaviors and phase compositions of titanium-bearing slag

The effects of MgO and TiO₂ on the viscosity, activation energy for viscous flow, and break-point temperature of titanium-bearing slag were studied. The correlation between viscosity and slag structure was analyzed by Fourier transform infrared (FTIR) spectroscopy. Subsequently, main phases in the slag and their content changes were investigated by X-ray diffraction and Factsage 6.4 software package. The results show that the viscosity decreases when the MgO content increases from 10.00wt% to 14.00wt%. Moreover, the break-point temperature increases, and the activation energy for viscous flow initially increases and subsequently decreases. In addition, with increasing TiO₂ content from 5.00wt% to 9.00wt%, the viscosity decreases, and the break-point temperature and activation energy for viscous flow initially decrease and subsequently increase. FTIR analyses reveal that the polymerization degree of complex viscous units in titanium-bearing slag decreases with increasing MgO and TiO₂ contents. The mechanism of viscosity variation was elucidated. The basic phase in experimental slags is melilite. Besides, as the MgO content increases, the amount of magnesia–alumina spinel in the slag increases. Similarly, the sum of pyroxene and perovskite phases in the slag increases with increasing TiO₂ content.     

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.     

Application prospects of high-voltage cathode materials in all-solid-state lithium-ion batteries

All-solid-state lithium-ion batteries are lithiumion batteries with solid-state electrolytes instead of liquid electrolytes.They are hopeful in solving the safety problems of lithium-ion batteries,once their large capacity and long life are achieved,they will have broad application prospects in the field of electric vehicles and large-scale energy storage.The working potential window of solid electrolytes is wider than that of liquid electrolytes,so high-voltage cathode materials could be used in all-solidstate lithium-ion batteries to get higher energy density and larger capacity by elevating the working voltage of the batteries.The spinel LiNi0.5Mn1.5O4material,layered Li–Ni–Co–Mn–O cathode materials and lithium-rich cathode materials can be expected to be applied to all-solid-state lithium-ion batteries as cathode materials due to their highvoltage platforms.In this review,the electrochemical properties and structures of spinel LiNi0.5Mn1.5O4material,layered Li–Ni–Co–Mn–O cathode materials and lithiumrich cathode materials are introduced.More attentions are paid on recent research progress of conductivity and interface stability of these materials,in order to improve their compatibility with solid electrolytes as cathode materials in all-solid-state lithium-ion batteries and fully improve the properties of all-solid-state batteries.Finally,the existing problems of their application in all-solid-state lithium-ion batteries are summarized,the main research directions are put forward and their application prospects in all-solid-state lithium-ion batteries are discussed.     

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 Co substitution on the structural,dielectric and optical properties of KBiFe_2O_5

Cobalt(Co)-modified brownmillerite KBiFe_2O_5(KBFO; [KBiFe_(2(1-x))Co_(2x)O_5(x = 0, 0.05)]) polycrystalline is synthesized following the solid-state reaction route. Rietveld refinement of X-ray diffraction data confirmed the phase purity of KBFO and KBiFe_(1.9)Co_(0.1)O_5(KBFCO). The optical bandgap energy(Eg) of KBFO decreased from 1.59 to 1.51 e V because of Co substitution. The decrease in bandgap can be attributed to the tilting of the Fe–O tetrahedral structure of KBFCO. The observed room-temperature Raman peaks of KBFCO shifted by3 cm~(-1) toward a lower wavenumber than that of KBFO. The shift in Raman active modes can be attributed to the change in the bond angles and bond lengths of the Fe–O tetrahedral structure and modification in response to oxygen deficiency in KBFO because of Co doping. Compared with that of KBFO, the frequency-dependent dielectric constant and dielectric loss of KBFCO decrease at room temperature, which is a consequence of the reduction in oxygen migration and modification in response to vibrational modes present in the sample.     

Effect of TiO_2 on the viscosity and structure of low-fluoride slag used for electroslag remelting of Ti-containing steels

The viscosity of CaF_2–CaO–Al_2O_3–MgO–(TiO_2) slag was measured using a rotating crucible viscometer. Raman spectroscopy analysis was performed to correlate the viscosity to slag structure. The viscosity of the slag was found to decrease with increasing TiO_2 content in the slag from 0 to 9.73wt%. The activation energy decreased from 95.16 kJ /mol to 79.40 kJ /mol with increasing TiO_2 content in the slag. The introduction of TiO_2 into the slag played a destructive role in Al–O–Al structural units and Q~4 units by forming simpler structural units of Q~2 and Ti_2O_6~(4-) chain. The amount of Al–O–Al significantly decreased with increasing TiO_2 content. The relative fraction of Q~4 units in the [AlO_4]~(5-)-tetrahedral units shows a decreasing trend, whereas the relative fraction of Q~2 units and Ti_2O_6~(4-) chain increases with increasing TiO_2 content accordingly. Consequently, the polymerization degree of the slag decreases with increasing TiO_2 content. The variation in slag structure is consistent with the change in measured viscosity.     

Electrical conductivity optimization of the Na_3AlF_6–Al_2O_3–Sm_2O_3 molten salts system for Al–Sm intermediate binary alloy production

Metal Sm has been widely used in making Al–Sm magnet alloy materials. Conventional distillation technology to produce Sm has the disadvantages of low productivity, high costs, and pollution generation. The objective of this study was to develop a molten salt electrolyte system to produce Al–Sm alloy directly, with focus on the electrical conductivity and optimal operating conditions to minimize the energy consumption. The continuously varying cell constant(CVCC) technique was used to measure the conductivity for the Na_3 AlF_6–AlF_3–LiF–MgF_2–Al_2O_3–Sm_2O_3 electrolysis medium in the temperature range from 905 to 1055°C. The temperature(t) and the addition of Al_2O_3(W(Al_2O_3)), Sm_2O_3(W(Sm_2O_3)), and a combination of Al_2O_3 and Sm_2O_3 into the basic fluoride system were examined with respect to their effects on the conductivity(κ) and activation energy. The experimental results showed that the molten electrolyte conductivity increases with increasing temperature(t) and decreases with the addition of Al_2O_3 or Sm_2O_3 or both. We concluded that the optimal operation conditions for Al–Sm intermediate alloy production in the Na_3 AlF_6–AlF_3–LiF–MgF_2–Al_2O_3–Sm_2O_3 system are W(Al_2O_3) + W(Sm_2O_3) = 3wt%, W(Al_2O_3):W(Sm_2O_3) = 7:3, and a temperature of 965 to 995°C, which results in satisfactory conductivity, low fluoride evaporation losses, and low energy consumption.     

Dielectric properties, electrical modulus and current transport mechanisms of Au/ZnO/n-Si structures

Au/Zn O/n-Si(MIS)structures were fabricated by using the RF sputtering method and their complex dielectric constant(ε~*=ε’-jε’’),electric modulus(M~*=M′+j M’’)and electrical conductivity(σ=σ_(dc)+σ_(ac))values were investigated as a function of frequency(0.7 k Hz-1 MHz)and voltage(-6–(+6 V))by capacitance-voltage(C-V)and conductance-voltage(G/ω-V)measurements to get more information on the conduction mechanisms and formation of barrier height between Au and n-Si.The lnσ-Lnf plots have two different regions corresponding to low-intermediate and high frequencies.Such behavior of lnσ-lnf plots shows that the existence of two different conduction mechanisms(CMs)at low-intermediate and high frequencies.Moreover,the reverse bias saturation current(I_o),ideality factor(n),barrier height(Φ_(Bo))were determined from the forward bias I-V data and they were found as a strong function of temperature.The value of n especially at low temperature is considerably higher than unity.The values ofΦ_(B0)and standard deviation(σ_s)were found from the intercept and slope ofΦ_(Bo)-q/2k T plots as 0.551 e V and 0.075 V for the region I(80–220 K)and 1.126 e V and 0.053 V for the region II(220–400 K),respectively.The values ofΦ_(Bo)and effective Richardson constant(A~*)were found from slope and intercept of activation energy plots as 0.564 e V and 101.084 Acm~(-2)K~(-2)for the region I and 1.136 e V and41.87 Acm~(-2)K~(-2)for the region II,respectively.These results confirm that the current-voltage-temperature(I-V-T)characteristics of the fabricated Au/Zn O/n-Si SBDs can satisfactorily be explained on the basis of TE theory with double GD of the BHs.     

Fabrication of SrFe_(12-x)Ni_xO_(19) nanoparticles and investigation on their structural,magnetic and dielectric properties

Sr Fe12-xNixO19 nanoparticles(x = 0–1) were synthesized by a combustion sol–gel method. Their structure, dielectric and magnetic properties were investigated by X-ray diffraction(XRD), scanning electron microscopy(SEM), an LCR metry, and vibrating sample magnetometry(VSM).The results reveal that all samples of Ni doped compounds(Sr Fe12-xNixO19) with x 0.2 are single phase. It appears that the Fe3+ ions are substituted by Ni2+ ions on the crystallographic sites of the Sr Fe12O19 structure; however, for x ≥ 0.2, the secondary Ni phase ferrite(Ni Fe2O3) appears, which reduces the saturation magnetization and coercivity. In addition, Ni doping reduces the dielectric constant, dielectric loss, and alternating current(ac) electrical conductivity of the samples. The variation in ac conductivity(σac) with frequency shows that the electrical conductivity in these ferrites is mainly attributed to the electron hopping mechanism.Therefore; all the single-phase Ni doped samples are suitable for use in magnetic recording media and microwave devices.     

Effect of the CaO/SiO_2 mass ratio and FeO content on the viscosity of CaO–SiO_2–“FeO”–12wt%ZnO–3wt%Al_2O_3 slags

An effective process for recycling lead from hazardous waste cathode ray tubes(CRTs) funnel glass through traditional lead smelting has been presented previously. The viscous behavior of the molten high lead slag, which is affected by the addition of funnel glass, plays a critical role in determining the production efficiency. Therefore, the viscosities of the CaO–SiO_2–"FeO"–12wt%ZnO–3wt%Al_2O_3 slags were measured in the current study using the rotating spindle method. The slag viscosity decreases as the CaO/SiO_2 mass ratio is increased from 0.8 to 1.2 and also as the FeO content is increased from 8wt% to 20wt%. The breaking temperature of the slag is lowered substantially by the addition of FeO, whereas the influence of the CaO/SiO_2 mass ratio on the breaking temperature is complex. The structural analysis of quenched slags using Fourier transform infrared(FTIR) spectroscopy and Raman spectroscopy reveals that the silicate network structure is depolymerized with increasing CaO/SiO_2 mass ratio or increasing FeO content. The [FeO_6]-octahedra in the slag melt increase as the CaO/SiO_2 mass ratio or the FeO content increases. This increase can further decrease the degree of polymerization(DOP) of the slag. Furthermore, the activation energy for viscous flow decreases both with increasing CaO/SiO_2 mass ratio and increasing FeO content.     

Effect of Yb_2O_3 doping on the grain boundary of NiFe_2O_4–10NiO-based cermets after sintering

xY b2O3–15(20Ni–Cu)/(85- x)(NiF e2O4–10NiO)(x = 0, 0.25, 0.5, 0.75, 1.0, 2.0, and 10.0) cermets for aluminum electrolysis were prepared to investigate the effect of Yb2O3 doping on the grain boundary of the cermets after sintering. The results showed that each interface was very clear and that with increasing Yb2O3 content, most of the Yb was evenly distributed at the grain boundary. Moreover, according to the phase composition and microstructural analysis by X-ray diffraction(XRD), scanning electron microscopy with energy dispersive X-ray spectroscopy(SEM/EDX), and electron probe microanalysis(EPMA), YbF eO 3 was produced along the grain boundary. The YbF eO 3 was concluded to not only have formed from the interaction between the NiF e2O4 or Fe2O3 component and Yb2O3 at the grain boundary of the cermets, but also from the decomposition of NiF e2O4 into NiO and Fe2O3 and the subsequent reaction of Fe2O3 with Yb2O3. Thus, the production of YbF eO 3 resulted in a cermet with high relative density, good electrical conductivity, and good corrosion resistance.     

Kinetics of petroleum coke/biomass blends during co-gasification

The co-gasification behavior and synergistic effect of petroleum coke, biomass, and their blends were studied by thermogravimetric analysis under CO₂ atmosphere at different heating rates. The isoconversional method was used to calculate the activation energy. The results showed that the gasification process occurred in two stages: pyrolysis and char gasification. A synergistic effect was observed in the char gasification stage. This effect was caused by alkali and alkaline earth metals in the biomass ash. Kinetics analysis showed that the activation energy in the pyrolysis stage was less than that in the char gasification stage. In the char gasification stage, the activation energy was 129.1–177.8 kJ/mol for petroleum coke, whereas it was 120.3–150.5 kJ/mol for biomass. We also observed that the activation energy calculated by the Flynn–Wall–Ozawa (FWO) method were larger than those calculated by the Kissinger–Akahira–Sunosen (KAS) method. When the conversion was 1.0, the activation energy was 106.2 kJ/mol when calculated by the KAS method, whereas it was 120.3 kJ/mol when calculated by the FWO method.