Improvement of sintering,nonlinear electrical,and dielectric properties of ZnO-based varistors doped with TiO_2

The effects of TiO_2 on sintering and nonlinear electrical properties of(98.5-x)ZnO–0.5MnO_2–0.5Co_2O_3-0.5Bi_2O_(3–x)TiO_2(x = 0.3,0.5,0.7,0.9 mol%) ceramic varistors prepared by the ceramic technique are investigated in this work.The optimum sintering temperature of the prepared samples is deduced by determining the firing shrinkage and water absorption percentages.The optimum sintering temperature is found to be 1200℃,at which each of the samples shows a maximum firing shrinkage and minimum water absorption.Also minimum water absorption appears in a sample of x = 0.9 mol%.Higher sintering temperature and longer sintering time give rise to a reduction in bulk density due to the increased amount of porosity between the large grains of ZnO resulting from the rapid grain growth induced by the liquid phase sintering.The crystal size of ZnO decreases with increasing TiO_2 doping.The addition of TiO_2 improves the nonlinear coefficient and attains its maximum value at x = 0.7 mol% of TiO_2,further addition negatively affects it.A decrease in capacitance consequently in the dielectric constant is recorded with increasing the frequency in a range of 30 kHz–200 kHz.The temperature and composition dependences of the dielectric constant and AC conductivity are also studied.The increase of temperature raises the dielectric constant because it increases ionic response to the field at any particular frequency.     

Temperature-Dependent Dynamic Properties of LixMn2O4 in Monte Carlo Simulations

Monte Carlo (MC) simulations are used to simulate the voltage profile and the ionic conductivity s of Li ions in LixMn2O4 and its dependence on the lithium concentration x. The open circuit potential shows clearly the two plateaus in the charge/discharge curve, which agrees well with the experimental results. The two plateaus become more and more steep when the temperature is increased. The simulated ionic conductivity shows an M-shaped curve in the plot of ionic conductivity cr versus x when the simulation temperature is low. Interestingly,the minimum valley, which lies at the middle single-phase area near x=0.5, disappears gradually when the temperature increases to 453K.     

Properties of negative thermal expansion β-eucryptite ceramics prepared by spark plasma sintering

β-eucryptite powders are prepared by the sol-gel method through using tetraethoxysilane lithium nitrate and aluminum isopropoxide as starting materials. β-eucryptite ceramics are prepared by spark plasma sintering. The effects of sintering temperature on the negative thermal expansion properties of the β-eucryptite are investigated by x-ray diffraction(XRD), scanning electron microscopy, and thermal expansion test. The XRD results exhibit no change in the crystal structure of the sample prepared by different sintering processes. The negative thermal expansion properties increase with the increase of the sintering temperature. The coefficient of thermal expansion of β-eucryptite ceramics sintered at 1100℃ is calculated to be -4.93 × 10~(-6)℃~(-1). Crystallization behaviors of the ceramics may play an important role in the increase of negative thermal expansion of β-eucryptite. High sintering temperature could improve the crystallization behaviors of the ceramics and reduce the residue glass phase, which can improve the negative thermal expansion properties of β-eucryptite ceramics.     

Elastic Modulus,Hardness,and Fracture Toughness of Li_(6.4)La_3Zr_(1.4)Ta_(0.6)O_(12) Solid Electrolyte

Li_(6.4)La_3 Zr_(1.4)Ta_(0.6)O_(12)(LLZTO) is a promising inorganic solid electrolyte due to its high Li+conductivity and electrochemical stability for all-solid-state batteries.Mechanical characterization of LLZTO is limited by the synthesis of the condensed phase.Here we systematically measure the elastic modules,hardness,and fracture toughness of LLZTO poly crystalline pellets of different densities using the customized environmental nanoindentation.The LLZTO samples are sintered using the hot-pressing method with different amounts of Li_2CO_3 additives,resulting in the relative density of the pellets varying from 83% to 98% and the largest grain size of 13.21 ± 5.22 μm.The mechanical properties show a monotonic increase as the sintered sample densifies,elastic modulus and hardness reach 158.47± 10.10 GPa and 11.27± 1.38 GPa,respectively,for LLZTO of 98% density.Similarly,fracture toughness increases from 0.44 to 1.51 MPa·m~(1/2),showing a transition from the intergranular to transgranular fracture behavior as the pellet density increases.The ionic conductivity reaches 4.54 × 10~(-4) S/cm in the condensed LLZTO which enables a stable Li plating/stripping in a symmetric solid-state cell for over 100 cycles.This study puts forward a quantitative study of the mechanical behavior of LLZTO of different microstructures that is relevant to the mechanical stability and electrochemical performance of all-solid-state batteries.     

Effects of Li Substitution and Sintering Temperature on Properties of Bi0.5（Na,K）0.5TiO3 Lead-Free Piezoelectric Ceramics

Bi0.5 （Na0.72K0.28- x Lix ）0.5 TiO3 （BNKLT- 100x） lead-free piezoelectric ceramics are synthesized by conventional solid state sintering techniques. The dielectric and piezoelectric properties of the BNKLT-100x ceramics as a function of Li content are systematically investigated. It is found that not only Li content but also the sintering temperature has a strong effect on the piezoelectric properties of BNKLT. The piezoelectric constant d33 Of BNKLT varies from 120 to 252pC/N in the Li content range from 0.03 to 0.16. In the sintering temperature range from 1080 to 1130℃, the d33 value of BNKLT-6 changes from 200pC/N to 252pC/N. The BNKLT-6 sample sintered at 1100℃ has the highest piezoelectric constant d33 of 252pC/N, with the electromechanical coupling factors kp of 0.32 and kt of 0.44.     

Tuning hybrid liquid/solid electrolytes by lowering Li salt concentration for lithium batteries

Hybrid liquid/solid electrolytes(HLSEs) consisting of conventional organic liquid electrolyte(LE), polyacrylonitrile(PAN), and ceramic lithium ion conductor Li_(1.5)Al_(0.5)Ge_(1.5)(PO_4)_3(LAGP) are proposed and investigated. The HLSE has a high ionic conductivity of over 2.25 × 10~(-3) S/cm at 25?C, and an extended electrochemical window of up to 4.8 V versus Li/Li+. The Li|HLSE|Li symmetric cells and Li|HLSE|Li FePO_4 cells exhibit small interfacial area specific resistances(ASRs) comparable to that of LE while much smaller than that of ceramic LAGP electrolyte, and excellent performance at room temperature. Bis(trifluoromethane sulfonimide) salt in HLSE significantly affects the properties and electrochemical behaviors. Side reactions can be effectively suppressed by lowering the concentration of Li salt. It is a feasible strategy for pursuing the high energy density batteries with higher safety.     

Influences of spark plasma sintering temperature on the microstructures and thermoelectric properties of(Sr_(0.95)Gd_(0.05))TiO_3 ceramics

(Sr0.95Gd0.05)Ti O3(SGTO) ceramics are successfully prepared via spark plasma sintering(SPS) respectively at 1548,1648,and 1748 K by using submicron-sized SGTO powders synthesized from a sol–gel method.The densities,microstructures,and thermoelectric properties of the SGTO ceramics are studied.Though the Seebeck coefficient shows no obvious difference in the case that SPS temperatures range from 1548 K to 1648 K,the electrical conductivity and the thermal conductivity increase remarkably due to the increase in grain size and density.The sample has a density higher than 98%theoretical density as the sintering temperature increases up to 1648 K and shows average grain sizes increasing from～ 0.7 μm to 7 μm until 1748 K.As a result,the maximum of the dimensionless figure of merit of ～ 0.24 is achieved at～ 1000 K for the samples sintered at 1648 K and 1748 K,which was ～ 71% larger than that(0.14 at ～ 1000 K) for the sample sintered at 1548 K due to the enhancement of the power factor.     

The low-temperature sintering and microwave dielectric properties of （Zno.7Mgo.3） TiO3 ceramics with H3BO3

The effects of the addition of H3BO3 on the microstructure, phase formation, and microwave dielectric properties of （Zn0.TMg0.3）TiO3 ceramics sintered at temperatures ranging from 890 ℃ to 950 ℃ are investigated. H3BO3 as a sintering agent can effectively lower the sintering temperature of ZMT ceramics below 950 ℃due to the liquid-phase effect. The microwave dielectric properties are found to strongly correlate with the amount of H3BO3. With the increase in H3BO3 content, the dielectric constant （er） monotonically increases, but the quality factor （Q x f） reaches a maximum at 1 wt% H3BO3, and the apparent density of ZMT ceramics with H3BO3〉 1 wt% gradually decreases. At 950 ℃, the ZMT ceramics with 1% H3BO3 exhibit excellent microwave dielectric properties： er = 19.8, and Q x f -- 43800 GHz （8.94 GHz）.     

Crystal structure and ionic conductivity of Mg-doped apatite-type lanthanum silicates LaloSi6-xMgxO27-x （x= 0-0.4）

Lanthanum silicates LaloSi6 xMgxO27_x （x = 0-0.4） were prepared by solid state synthesis to investigate the effect of Mg doping on crystal structure and ionic conductivity. Rietveld analysis of the powder XRD patterns reveals that Mg substitution on Si site results in significant enlargement of channel triangles, favoring oxide-ion conduction. Furthermore, an increase of Mg concentration significantly influences the linear density of interstitial oxygen, which plays an important role in ionic conductivity. The Arrhenius plots of LaloSi6_xMgxO27 x （x = 0-0.4） suggest that Mg-doped samples present higher conductivity and lower activation energy than non-doped La10Si6027, and LaloSis.8Mgo.2026.8 exhibits the highest conductivity with a value of 3.0× 10-2 S .cm 1 at 700 ℃. Such conductive behavior agrees well with the refined results. The corresponding mechanism has been discussed in this paper.     

Correlation of Lithium Ionic Diffusion with Nb Concentration in Li7-xLa3Zr2-xNbxO12 Evaluated by an Internal Friction Method

Solid lithium-ion conductors Li7-xLa3Zr2-xNbxO12（x =0.25, 0.5, 1, 1.5） with cubic garnet structure are suc- cessfully prepared by a solid state reaction method, and the effects of Nb concentration on lithium ion diffusion are investigated by means of internal friction （IF） technique. A prominent relaxation-type IF peak （actually composed of two components） is observed in each Nb doped LiTLa3Zr2012 compound： with apeak PL at lower temperature and a peak PH at higher temperature. The mechanisms of the two components are suggested to be associated with two diffusion processes of lithium ions via vacancies： 48g ←→ 48g and 489 ←→ 24d. The relaxational strength of the IF peak gradually decreases, which is accompanied by the activation energy increasing from 0.45 eV to 0.64 eV with the increasing Nb doping level. The corresponding mechanism is ascribed to originate from lattice contraction as well as the lower concentration of diffusion ions induced by the substitution of Zr4＋ by Nb5＋.     

Effects of BaCu（B2Os） addition on sintering temperature and microwave dielectric properties of BasNb4O15-BaWO4 ceramics

The effects of BaCu（B2Os） （BCB） addition on the microstructure, phase formation, and microwave dielectric proper- ties of BasNb4015-BaWO4 ceramic are investigated. As a sintering aid, BaCu（B2Os） ceramic could effectively lower the sintering temperature of BasNb4015-BaWO4 ceramic from 1100 ℃ to 950 ℃ due to the liquid-phase effect. Meanwhile, BaCu（B2Os） addition effectively improves the densification of BasNb4015-BaWO4 ceramic and significantly influences the microwave dielectric properties. X-ray diffraction analysis reveals that BasNb4015 and BaWO4 coexist with no crystal phase of BaCu（B2Os） in the sintered ceramics. The BasNb4015-BaWO4 ceramics with 1.0 wt% BaCu（B2Os） sintered at 950 ℃ for 2 h presents good microwave dielectric properties of er = 19.0, high Q× f of 33802 GHz and low vf of 2.5 ppm/℃.     

Computational screening of doping schemes for LiTi2(PO4)3 as cathode coating materials

In all-solid-state lithium batteries,the impedance at the cathode/electrolyte interface shows close relationship with the cycle performance.Cathode coatings are helpful to reduce the impedance and increase the stability at the interface effectively.LiTi2(PO4)3(LTP),a fast ion conductor with high ionic conductivity approaching 10^-3S·cm^-1,is adopted as the coating materials in this study.The crystal and electronic structures,as well as the Li^+ion migration properties are evaluated for LTP and its doped derivatives based on density functional theory(DFT)and bond valence(BV)method.Substituting part of Ti sites with element Mn,Fe,or Mg in LTP can improve the electronic conductivity of LTP while does not decrease its high ionic conductivity.In this way,the coating materials with both high ionic conductivities and electronic conductivities can be prepared for all-solid-state lithium batteries to improve the ion and electron transport properties at the interface.     

Conductivity and applications of Li-biphenyl-1,2-dimethoxyethane solution for lithium ion batteries

The total conductivity of Li-biphenyl-1,2-dimethoxyethane solution(Li_xBp(DME)_(9.65), Bp = biphenyl, DME = 1,2-dimethoxyethane, x = 0.25, 0.50, 1.00, 1.50, 2.00) is measured by impedance spectroscopy at a temperature range from 0℃ to 40℃. The Li_(1.50)Bp(DME)_(9.65) has the highest total conductivity 10.7 m S/cm. The conductivity obeys Arrhenius law with the activation energy(E_(a(x=0.50))= 0.014 eV, E_(a(x=1.00))= 0.046 eV). The ionic conductivity and electronic conductivity of Li_xBp(DME)_(9.65) solutions are investigated at 20℃ using the isothermal transient ionic current(ITIC) technique with an ion-blocking stainless steal electrode. The ionic conductivity and electronic conductivity of Li_(1.00)Bp(DME)_(9.65) are measured as 4.5 mS/cm and 6.6 mS/cm, respectively. The Li_(1.00)Bp(DME)_(9.65) solution is tested as an anode material of half liquid lithium ion battery due to the coexistence of electronic conductivity and ionic conductivity. The lithium iron phosphate(LFP) and Li_(1.5)Al_(0.5)Ti_(1.5)(PO_4)_3(LATP) are chosen to be the counter electrode and electrolyte, respectively. The assembled cell is cycled in the voltage range of 2.2 V-3.75 V at a current density of 50 mA/g. The potential of Li_(1.00)Bp(DME)_(9.65) solution is about 0.3 V vs. Li~+/Li, which indicates the solution has a strong reducibility. The Li_(1.00)Bp(DME)_(9.65) solution is also used to prelithiate the anode material with low first efficiency, such as hard carbon, soft carbon and silicon.     

Thermoelectric properties of Li-doped Sr_(0.7)Ba_(0.3)Nb_2O_(6-δ) ceramics

Thermoelectric properties of Li-dopedSr_(0.7)Ba_(0.3)Nb_2O_(6-δ)ceramics were investigated in the temperature range from 323 K to 1073 K. The electrical conductivity increases significantly after lithium interstitial doping. However, both of the magnitudes of Seebeck coefficient and electrical conductivity vary non-monotonically but synchronously with the doping contents, indicating that doped lithium ions may not be fully ionized and oxygen vacancy may also contribute to carriers. The lattice thermal conductivity increases firstly and then decreases as the doping content increases, which is affected by competing factors.Thermoelectric performance is enhanced by lithium interstitial doping due to the increase of the power factor and the thermoelectric figure of merit reaches maximum value(0.21 at 1073 K) in the sample Sr_(0.70)Ba_(0.30)Li_(0.10)Nb_2O_6.     

键价和方法计算离子输运通道筛选锂离子无机固体电解质（英文）

Inorganic solid electrolytes have distinguished advantages in terms of safety and stability,and are promising to substitute for conventional organic liquid electrolytes.However,low ionic conductivity of typical candidates is the key problem.As connective diffusion path is the prerequisite for high performance,we screen for possible solid electrolytes from the 2004 International Centre for Diffraction Data(ICDD)database by calculating conduction pathways using Bond Valence(BV)method.There are 109846 inorganic crystals in the 2004 ICDD database,and 5295 of them contain lithium.Except for those with toxic,radioactive,rare,or variable valence elements,1380 materials are candidates for solid electrolytes.The rationality of the BV method is approved by comparing the existing solid electrolytes’conduction pathways we had calculated with those from experiments or first principle calculations.The implication for doping and substitution,two important ways to improve the conductivity,is also discussed.Among them Li2CO3 is selected for a detailed comparison,and the pathway is reproduced well with that based on the density functional studies.To reveal the correlation between connectivity of pathways and conductivity,/-LiAlO2 and Li2CO3 are investigated by the impedance spectrum as an example,and many experimental and theoretical studies are in process to indicate the relationship between property and structure.The BV method can calculate one material within a few minutes,providing an efficient way to lock onto targets from abundant data,and to investigate the structure-property relationship systematically.     

Effect of Nb doping on microstructures and thermoelectric properties of SrTiO_3 ceramics

Nb-doped SrTiO_3 thermoelectric ceramics with different niobium concentrations,sintering temperatures and Sr-site vacancies are successfully prepared by high energy ball milling combined with carbon burial sintering.For fully understanding the effect of niobium doping on SrTiO_3,thermoelectric transport properties are systematically investigated in a temperature range from 300 K to 1100 K.The carrier mobility can be significantly enhanced,and the electrical conductivity is quadrupled,when the sintering temperature rises from 1673 K to 1773 K(beyond the eutectic temperature(1713 K) of SrTiO_3–TiO_2).The lattice vibration can be suppressed by the lattice distortion introduced by the doped niobium atoms.However,Sr-site vacancies compensate for the lattice distortion and increase the lattice thermal conductivity more or less.Finally,we achieve a maximum value of figure-of-merit z T of 0.21 at 1100 K for Sr Ti_(0.9)Nb_(0.1)O_3 ceramic sintered at1773 K.     

The low-temperature sintering and microwave dielectric properties of (Zn_(0.7)Mg_(0.3))TiO_3 ceramics with H_3BO_3

The effects of the addition of H 3 BO 3 on the microstructure, phase formation, and microwave dielectric properties of (Zn 0.7 Mg 0.3 )TiO 3 ceramics sintered at temperatures ranging from 890 ℃ to 950 ℃ are investigated. H 3 BO 3 as a sintering agent can effectively lower the sintering temperature of ZMT ceramics below 950 ℃ due to the liquid-phase effect. The microwave dielectric properties are found to strongly correlate with the amount of H 3 BO 3 . With the increase in H 3 BO 3 content, the dielectric constant (ε r ) monotonically increases, but the quality factor (Q × f ) reaches a maximum at 1 wt% H 3 BO 3 , and the apparent density of ZMT ceramics with H 3 BO 3 ≥ 1 wt% gradually decreases. At 950 ℃, the ZMT ceramics with 1% H 3 BO 3 exhibit excellent microwave dielectric properties: ε r = 19.8, and Q × f = 43800 GHz (8.94 GHz).     

Structural and dielectric properties of giant dielectric Na_(1/2)Sm_(1/2)Cu_3Ti_4O_(12) ceramics prepared by reactive sintering methods

Na_(0.5)Sm_(0.5)Cu_3Ti_4O_(12)(NSCTO) ceramics have been prepared by reactive sintering of amorphous powder.Spark plasma sintering(SPS) for 10 min at 1025℃ and conventional sintering(CS) for 10 h at 1090℃ have been employed.X-ray diffraction measurements confirmed the pure CCTO-like phase for SPS and CS NSCTO ceramics.The SPS ceramic showed an average grain size of 500 nm, which is much smaller than that of the CS(～ 5 μm) sample.The impedance spectroscopy measurements revealed an electrically inhomogeneous structure in the prepared ceramics.While the resistivities of grains of both ceramic samples were in the same order of magnitude, the resistivity of grain-boundaries of the CS ceramic was three orders of magnitude greater than that of the SPS ceramic.Both of the samples showed giant dielectric constant( 10~3) over wide ranges of temperatures and frequencies.Nevertheless, the room-temperature dielectric loss of the SPS NSCTO(3.2 at 1.1 kHz) ceramic sample was higher than that of the CS NSCTO(0.08 at 1.1 kHz) ceramic sample due to the reduced grain-boundary resistivity of the former.Two dielectric relaxations were detected for each sample and attributed to the relaxations in grains and grain-boundaries.The dielectric behavior of the SPS and CS NSCTO ceramics could be interpreted in terms of the internal barrier layer capacitor(IBLC) model.     

Crystal structure and ionic conductivity of Mg-doped apatite-type lanthanum silicates La10Si6-x Mgx O27-x（x=0–0.4）

Lanthanum silicates La10Si6-xMgxO27-x(x = 0–0.4) were prepared by solid state synthesis to investigate the effect of Mg doping on crystal structure and ionic conductivity. Rietveld analysis of the powder XRD patterns reveals that Mg substitution on Si site results in significant enlargement of channel triangles, favoring oxide-ion conduction. Furthermore,an increase of Mg concentration significantly influences the linear density of interstitial oxygen, which plays an important role in ionic conductivity. The Arrhenius plots of La10Si6-xMgxO27-x(x = 0–0.4) suggest that Mg-doped samples present higher conductivity and lower activation energy than non-doped La10Si6O27, and La10Si5.8Mg0.2O26.8exhibits the highest conductivity with a value of 3.0×10-2S ·cm-1at 700?C. Such conductive behavior agrees well with the refined results.The corresponding mechanism has been discussed in this paper.     

Characterization of the BaBiO3-doped BaTiO3 positive temperature coefficient of a resistivity ceramic using impedance spectroscopy with Tc=155℃

BaBiO 3-doped BaTiO3(BB-BT) ceramic,as a candidate for lead-free positive temperature coefficient of resistivity (PTCR) materials with a higher Curie temperature,has been synthesized in air by a conventional sintering technique. The temperature dependence of resistivity shows that the phase transition of the PTC thermistor ceramic occurs at the Curie temperature,Tc=155℃,which is higher than that of BaTiO3(≤130℃). Analysis of ac impedance data using complex impedance spectroscopy gives the alternate current (AC) resistance of the PTCR ceramic. By additional use of the complex electric modulus formalism to analyse the same data,the inhomogeneous nature of the ceramic may be unveiled. The impedance spectra reveal that the grain resistance of the BB-BT sample is slightly influenced by the increase of temperature,indicating that the increase in overall resistivity is entirely due to a grain-boundary effect. Based on the dependence of the extent to which the peaks of the imaginary part of electric modulus and impedance are matched on frequency,the conduction mechanism is also discussed for a BB-BT ceramic system.