ITO thin films were grown on PC(polycarbonate), PMMA(polymethyl methacrylate) and glass substrates by r.f. magnetron sputtering. The electrical, structural and chemical characteristics of ITO films were analyzed b...ITO thin films were grown on PC(polycarbonate), PMMA(polymethyl methacrylate) and glass substrates by r.f. magnetron sputtering. The electrical, structural and chemical characteristics of ITO films were analyzed by the Hall Technique, X-ray diffraction, and X-ray photoelectron spectroscopy. XPS studies suggest that all the ITO films consist of crystalline and amorphous phases. The degree of crystallinity increases from less than 45% to more than 90% when the substrate temperature increases from 80 to 300 ℃. The In and Sn exist in the chemical state of In^3+ and Sn^4+, respectively, independent of substrate type and temperature. The enrichment of Sn on surface and In in body of ITO films are also revealed. And, the oxygen deficient regions exist both in surface layer and film body. For ITO films deposited under 180 ℃ , the carrier concentration are mainly provided by oxygen vacancies, and the dominant electron carrier scattering mechanism is grain boundary scattering between the crystal and the amorphous grain. For ITO films deposited over 180 ℃, the carrier concentration are provided by tin doping, and the dominant scattering mechanism transforms from grain boundary scattering between the crystal grains to ionized impurity scattering with increasing deposition temperature.展开更多
Nano-scale titanium oxide memristors exhibit complex conductive characteristics, which have already been proved by existing research. One possible reason for this is that more than one mechanism exists, and together t...Nano-scale titanium oxide memristors exhibit complex conductive characteristics, which have already been proved by existing research. One possible reason for this is that more than one mechanism exists, and together they codetermine the conductive behaviors of the memristor. In this paper, we first analyze the theoretical base and conductive process of a memristor, and then propose a compatible circuit model to discuss and simulate the coexistence of the dopant drift and tunnel barrier-based mechanisms. Simulation results are given and compared with the published experimental data to prove the possibility of the coexistence. This work provides a practical model and some suggestions for studying the conductive mechanisms of memristors.展开更多
The microstructure and conductive mechanism of high density polyethylene/carbon black (HDPE/CB) composite were investigated by positron annihilation lifetime spectroscopy (PALS). The PALS were measured in two series o...The microstructure and conductive mechanism of high density polyethylene/carbon black (HDPE/CB) composite were investigated by positron annihilation lifetime spectroscopy (PALS). The PALS were measured in two series of samples, one with various CB contents in the composites and the other with various gamma-irradiation doses in HDPE/CB composite containing 20 wt% CB. It was found that CB particles distribute in the amorphous regions, the CB critical content value in HDPE/CB composite is about 16.7 wt% and the suitable gamma-irradiation dose for improving the conductive behavior of HDPE/CB composite is about 20 Mrad. The result observed for the second set of samples suggests that gamma-irradiation causes not only cross-linking in amorphous regions but also destruction of the partial crystalline structure. Therefore, a suitable irradiation dose, about 20 Mrad, can induce sufficient cross-linking in the amorphous regions without enhancing the decomposition of crystalline structure, so that the positive temperature coefficient (PTC) effect remains while the negative temperature coefficient (NTC) effect is suppressed. A new interpretation of the conductive mechanism, which might provide a more detailed explanation of the PTC effect and the NTC effect has been proposed.展开更多
Transparent conducting F-doped texture SnO2 films with resistivity as low as 5× 10-4 Ω ·cm,with carrier concentrations between 3.5 × 1020 and 7× 1020 cm-3 and Hall mobilities from 15.7 to 20.1 cm2...Transparent conducting F-doped texture SnO2 films with resistivity as low as 5× 10-4 Ω ·cm,with carrier concentrations between 3.5 × 1020 and 7× 1020 cm-3 and Hall mobilities from 15.7 to 20.1 cm2/(V/s) have been prepared by atmosphere pressure chemical vapour deposition (APCVD). These polycrystalline films possess a variable preferred orientation, the polycrystallite sizes and orientations vary with substrate temperature. The substrate temperature and fluorine flow rate dependence of conductivity, Hall mobility and carrier conentration fOr the resultingfilms have been obtained. The temperature dependence of the mobiity and carrier concentrationhave been measured over a temperature range 16~400 K. A systematically theoretical analysis on scattering mechanisms for the highly conductive SnO2 films has been given. Both theoretical analysis and experimental results indicate that for these degenerate, polycrystalline SnO2 :F films in the low temperature range (below 100 K), ionized impurity scattering is main scattering mechanism. However, when the temperature is higher than 100 K, the lattice vibration scattering becomes dominant. The grain boundary scattering makes a small contribution to limit the mobility of the films.展开更多
The conductivity of non-crystalline fast ionic conductor for B_2O_3-Li_2O-LiCl-Al_2O_3 system is studiedin this paper. The glass structure of this system is discussed by means of infrared spectrum and X-ray fluorescen...The conductivity of non-crystalline fast ionic conductor for B_2O_3-Li_2O-LiCl-Al_2O_3 system is studiedin this paper. The glass structure of this system is discussed by means of infrared spectrum and X-ray fluorescence analysis, and the effects of LiCl and A1_2O_3 on the conductivity of Li^+ in the system are studied as well. Adding Li_2O to the system gives rise to transfer from [BO_3] triangular units to [BO_4] tetrahedral. When Li_2O content exceeds 30mol%, the main group of the glass is the diborate group with more [BO_4] tetrahedra. The adding of LiCl has no obvious influence on the glass structure, and LiCl is under a state dissociated by network, but with the increase of LiCl, the increase of conductivity is obvious. By adding A1_2O_3, the glass can be formed when the room-temperature is cooling down,the conductivity decreases while the conductive activatory energy increases for the glass. The experiment shows that conductivity in the room-temperature is σ= 6.2×10^(-6)Ω^(-1)cm^(-1), when at 300℃, the σ=6.8×10^(-3)Ω^(-1)cm^(-1). The conductive activatory energy computed is 0.6~1.0eV.展开更多
Na_(5+x) YAl_x Si_(4-x) O_(12) polycrystalline solid electrolytes are prepared by solid reactions. By the analyses of X-ray, TG and DTA, infrared spectu re, and SEM, the variasion of their density with the composition...Na_(5+x) YAl_x Si_(4-x) O_(12) polycrystalline solid electrolytes are prepared by solid reactions. By the analyses of X-ray, TG and DTA, infrared spectu re, and SEM, the variasion of their density with the composition X are discussed Their electric conductivity in the temperature range of R. T. to 300℃ are determined with electric brigde, and their variasions with the compositions X and temperature are studied. Their activations in the tem- perature range 140℃ to 300℃ are calculated, and their variation with the compositons X are discussed.展开更多
High thermal conductivity dense silica bricks have the higher thermal conductivity than ordinary silica bricks,which is conducive to the realization of energy saving and emission reduction in the iron and steel indust...High thermal conductivity dense silica bricks have the higher thermal conductivity than ordinary silica bricks,which is conducive to the realization of energy saving and emission reduction in the iron and steel industry.The performance of ordinary silica bricks and high thermal conductivity dense silica bricks was compared,and the high thermal conductivity mechanism was analyzed.The results show that(1)compared with ordinary silica bricks,high thermal conductivity dense silica bricks have the characteristics of higher thermal conductivity,lower apparent porosity,higher tridymite content,higher compressive strength,and higher thermal expansion;(2)by increasing the tridymite content and reducing the porosity,the close packing of honeycombα-tridymite improves the density and continuity of the SiO_(2)frame structure of the silica bricks,and the larger area perpendicular to the heat transfer direction improves the thermal conductivity of the bricks;(3)the densification of the silica bricks also increases the thermal expansion of the bricks,but they still meet the standard requirements.展开更多
The electrical conductivities of single-crystal K-feldspar along three different crystallographic directions are investigated by the Solartron-1260 Impedance/Gain-phase analyzer at 873 K–1223 K and 1.0 GPa–3.0 GPa i...The electrical conductivities of single-crystal K-feldspar along three different crystallographic directions are investigated by the Solartron-1260 Impedance/Gain-phase analyzer at 873 K–1223 K and 1.0 GPa–3.0 GPa in a frequency range of 10-1 Hz–106 Hz. The measured electrical conductivity along the ⊥ [001] axis direction decreases with increasing pressure, and the activation energy and activation volume of charge carriers are determined to be 1.04 ± 0.06 e V and 2.51 ± 0.19 cm~3/mole, respectively. The electrical conductivity of K-feldspar is highly anisotropic, and its value along the⊥ [001] axis is approximately three times higher than that along the ⊥ [100] axis. At 2.0 GPa, the diffusion coefficient of ionic potassium is obtained from the electrical conductivity data using the Nernst–Einstein equation. The measured electrical conductivity and calculated diffusion coefficient of potassium suggest that the main conduction mechanism is of ionic conduction, therefore the dominant charge carrier is transferred between normal lattice potassium positions and adjacent interstitial sites along the thermally activated electric field.展开更多
To attain the objectives of carbon peaking and carbon neutrality,the development of stable and highperformance ion-conducting materials holds enormous relevance in various energy storage and conversion devices.Particu...To attain the objectives of carbon peaking and carbon neutrality,the development of stable and highperformance ion-conducting materials holds enormous relevance in various energy storage and conversion devices.Particularly,crystalline porous materials possessing built-in ordered nanochannels exhibit remarkable superiority in comprehending the ion transfer mechanisms with precision.In this regard,covalent organic frameworks(COFs)are highly regarded as a promising alternative due to their preeminent structural tunability,accessible well-defined pores,and excellent thermal/chemical stability under hydrous/anhydrous conditions.By the availability of organic units and the diversity of topologies and connections,advances in COFs have been increasing rapidly over the last decade and they have emerged as a new field of proton-conducting materials.Therefore,a comprehensive summary and discussion are urgently needed to provide an"at a glance"understanding of the prospects and challenges in the development of proton-conducting COFs.In this review,we target a comprehensive review of COFs in the field of proton conductivity from the aspects of design strategies,the proton conducting mechanism/features,the relationships of structure-function,and the application of research.The relevant content of theoretical simulation,advanced structural characterizations,prospects,and challenges are also presented elaborately and critically.More importantly,we sincerely hope that this progress report will form a consistent view of this field and provide inspiration for future research.展开更多
With the rapid development of high-end industries,the demand for high-temperature piezoelectric materials is significantly increasing.However,realizing the ultra-high performance to meet more ap-plications still faces...With the rapid development of high-end industries,the demand for high-temperature piezoelectric materials is significantly increasing.However,realizing the ultra-high performance to meet more ap-plications still faces major scientific and engineering challenges of our time.Here,a new Nb/Mn co-doped CaBi_(4)Ti_(4)O_(15)(CBT)high-temperature piezoelectric material system of CaBi_(4)Ti_(4-x)(Nb_(2/3)Mn_(1/3))_(x)O_(15)was synthesized by the conventional solid-state sintering method.The results show that the addition of the dopants tends to break the long-range ferroelectric chain and soften the flexibility of polarization,resulting in more distorted crystal structure and better ferroelectric properties of CBT ceramics.The ultra-high piezoelectric constant(d_(33)=26.8 pC/N)is thus attained in CBT-based ceramics with x=0.12,which is about several times larger than that of pure CBT ceramics.Moreover,numerous nano-sized layered domain structures that lie on the lateral plane of grains are observed in ceramics,with lower domain wall energy and better dynamic features under electric fields,mainly responsible for the origin of enhanced performance.Besides,excess dopants could make the conductivity mechanism of CBT ceramics transform from p-type to n-type,and also result in a shift of conduction relaxation mechanism from defect dipole rotation polarization to electron relaxation polarization.The work not only provides a promising candidate for high-temperature piezoelectric materials,but also opens a window for opti-mizing performance by tailoring domain structures using chemical modification.展开更多
Rapid development of energy,electrical and electronic technologies has put forward higher requirements for the thermal conductivities of polymers and their composites.However,the thermal conductivity coefficient(λ)va...Rapid development of energy,electrical and electronic technologies has put forward higher requirements for the thermal conductivities of polymers and their composites.However,the thermal conductivity coefficient(λ)values of prepared thermally conductive polymer composites are still difficult to achieve expectations,which has become the bottleneck in the fields of thermally conductive polymer composites.Aimed at that,based on the accumulation of the previous research works by related researchers and our research group,this paper proposes three possible directions for breaking through the bottlenecks:(1)preparing and synthesizing intrinsically thermally conductive polymers,(2)reducing the interfacial thermal resistance in thermally conductive polymer composites,and(3)establishing suitable thermal conduction models and studying inner thermal conduction mechanism to guide experimental optimization.Also,the future development trends of the three above-mentioned directions are foreseen,hoping to provide certain basis and guidance for the preparation,researches and development of thermally conductive polymers and their composites.展开更多
BN ceramic is an advanced engineering ceramics with excellent thermal shock resistance, good workability and excellent dielectricity.TiB 2 ceramic has excellent electric conductivity,high melting points, and corrosio...BN ceramic is an advanced engineering ceramics with excellent thermal shock resistance, good workability and excellent dielectricity.TiB 2 ceramic has excellent electric conductivity,high melting points, and corrosion resistance to molten metal.Therefore,the composite consisting of BN and TiB 2 ceramics is expected to have a combination of above mentioned properties,thereby can be used as self heating crucible.In this paper,hot pressing technology was used to fabricate the high performance BN TiB 2 composite materials.microstructure and electric conducting mechanism were studied,and the relationship between the microstructure and physical property was discussed.The results show that the microstructure of composites has a great influence on the physical property of composites.The BN TiB 2 composites with excellent mechanical strength and stable resistivity can be obtained by optimizing the processing parameter and controlling the microstructure of composites.展开更多
In view of the fact that safety production supervision of coal mines in China features low efficacy, this paper applies principles of cybernetics to simulate the dynamic process of safety supervision, and proposes tha...In view of the fact that safety production supervision of coal mines in China features low efficacy, this paper applies principles of cybernetics to simulate the dynamic process of safety supervision, and proposes that institutional variables be controlled to support intermediate goals, which in turn contribute to the ultimate safety production objective. Rather than focusing all attention on safety issues of working faces, supervising departments of coalmines are advised to pay much more attention to institutional factors that may impact people’s attitude and behavior, which are responsible for most coalmine accidents. It is believed that such a shift of attention can effectively reduce coalmining production accidents and greatly enhance supervision efficacy.展开更多
Metal-organic frameworks(MOFs),typically constructed with metallic nodes and organic linkers,have influenced the development of modular solid materials.Their adjustable molecular structure provides a remarkable variet...Metal-organic frameworks(MOFs),typically constructed with metallic nodes and organic linkers,have influenced the development of modular solid materials.Their adjustable molecular structure provides a remarkable variety of MOF-based solid-state structures towards diverse applications.However,the low conductivity of traditional MOFs extremely hinders their applications in electronic and electrochemical devices.The emerging conductive MOFs,generally possessing twodimensional layered structures,are endowed with both the structural merits of common MOFs and exceptional electronic/ionic conductivities.Besides,the selection and optimization of ligands and metal centers,as well as synthetic methods enormously affects the intrinsic conductivity of conductive MOFs.The distinctive crystal structures and superb conductivity promise their appealing applications in electrochemical energy-related fields.In the review,we mainly summarize representative crystal features,conducting mechanisms and recent advances in rational design and synthesis of conductive MOFs,along with their versatile applications as electrodes for electrochemical capacitors and rechargeable batteries,and as catalysts towards electrocatalysis.Finally,the involved challenges and future trends/prospects of the conductive MOFs for electrochemical energyrelated applications are further proposed.展开更多
Relations between the structure, ionic conductivity and dielectric properties of fluoride systems of different structures containing rare earth elements were presented. Superionic conductivities, by fluoride ions, of ...Relations between the structure, ionic conductivity and dielectric properties of fluoride systems of different structures containing rare earth elements were presented. Superionic conductivities, by fluoride ions, of fluorite-structured (MF2-REF3, M=Ba, Pb, RE=La-Lu, Sc, Y), orthorhombic (REF3, RE=Tb-Er, Y), tysonite-structured (REF3-MF2, RE=La-Nd, M=Sr), monoclinic (BaRE2Fs, RE=Ho-Yb, Y) fluoride single crystals and eutectic composites (LiF-REF3, RE=La-Gd, Y) were compared. Anisotropy of electrical properties of crystals with a lower symmetry was explained by modeling optimum ionic paths. For explanation of concentration dependences of fast ionic conductivity, models of aggregation of defects into clusters were proposed. In fluorite-structured crystals, the highest ionic conductivity was found for PbF2:7 mol% ScF3 (at 500 K, σ500=0.13 S/cm). In tysonite-structured crystals, the highest ionic conductivity was found for LaF3:3 mol% SrF2 (σ500=2.4×10^-2 S/cm). Different types of coordination polyhedrons and their different linking in orthorhombic and tysonite structure explained large differences between conductivities in both structures. Eutectic systems, prepared as directionally solidified composites, enabled to study some orthorhombic fluoride phases (GdF3, SmF3), which cannot be prepared as single crystals. An influence of the orthorhombic-tysonite phase transition on the ionic conductivity was shown.展开更多
A new glass system (Bi2O3)50(Fe2O3)10(Li2O)x(K2O)40-x, where x changes in steps of 5 mole fraction between 0 and 40, was selected to study the electrical relaxation and the mixed alkali effect (MAE) phenomen...A new glass system (Bi2O3)50(Fe2O3)10(Li2O)x(K2O)40-x, where x changes in steps of 5 mole fraction between 0 and 40, was selected to study the electrical relaxation and the mixed alkali effect (MAE) phenomena. Measurements of ac conductivity σac, dielectric permittivity ε′ and loss factor tanδ in the frequency range of 0.12~10^2 kHz and in the temperature range of 300~650 K were carried out. The temperature dependence of the ac conductivity shows a slow increasing rate at low temperature and high frequency and a rapid increase at high temperature and low frequency. At constant temperature, the ac conductivity is found to be proportional to ω^8, where s is the frequency exponent, which is less than 1. Analysis of the conductivity data and the frequency exponent shows that the overlapping large polaron tunnelling (OLPT) model of ions is the most favorable mechanism for the ac conduction in the present glass system. The ac response, the dc conductivity and dielectric relaxation have the same activation energy and they originate from the same basic transport mechanism. The results of the dielectric permittivity show no maximum peak in the temperature and frequency range studied. This absence of maximum peak is an indication of non-ferroelectric behavior of all the studied samples. The MAE has been detected in the ac conductivity, which is the same as the classical MAE in the dc conductivity. The electrical parameters such as dielectric permittivity ε′ and real dielectric modulus M′ show a typical minimum deviation from linearity by about two orders of magnitude. The loss factor tanδ and the imaginary dielectric modulus M″ are insignificantly dependent on composition even at the same transition temperature Tg.展开更多
To extend the application of carbon nanotubes (CNTs) and explore novel aluminum matrix composites,CNTs were coated by molybdenum layers using metal organic chemical vapor deposition,and then Mo-coated CNT (Mo-CNT)...To extend the application of carbon nanotubes (CNTs) and explore novel aluminum matrix composites,CNTs were coated by molybdenum layers using metal organic chemical vapor deposition,and then Mo-coated CNT (Mo-CNT)/Al composites were prepared by the combination processes of powder mixing and spark plasma sintering.The influences of powder mixing and Mo-CNT content on the mechanical properties and electrical conductivity of the composites were investigated.The results show that magnetic stirring is better than mechanical milling for mixing the Mo-CNTs and Al powders.The electrical conductivity of the composites decreases with increasing Mo-CNT content.When the Mo-CNT content is 0.5wt%,the tensile strength and hardness of Mo-CNT/Al reach their maximum values.The tensile strength of 0.5wt% Mo-CNT/Al increases by 29.9%,while the electrical conductivity only decreases by 7.1%,relative to sintered pure Al.The phase analysis of Mo-CNT/Al composites reveals that there is no formation of Al carbide in the composites.展开更多
The deformation potential theory for one-dimensional organic polymer is studied. This approximation is then used to calculate the mobilities of carriers and the conductivity of trans-polymonocyanoacetylene (PMCA). The...The deformation potential theory for one-dimensional organic polymer is studied. This approximation is then used to calculate the mobilities of carriers and the conductivity of trans-polymonocyanoacetylene (PMCA). The results of calculations are in fairly good agreement with experimental data.展开更多
Continuous CNT fibers have been directly fabricated in a speed of 50 m/h-400 m/h,based on an improved chemical vapor deposition method.As-prepared fibers are further post-treated by acid.According to the SEM images an...Continuous CNT fibers have been directly fabricated in a speed of 50 m/h-400 m/h,based on an improved chemical vapor deposition method.As-prepared fibers are further post-treated by acid.According to the SEM images and Raman spectra,the acid treatment results in the compaction and surface modification of the CNTs in fibers,which are beneficial for the electron and load transfer.Compared to the HNO3 treatment,HClSO_3 or H_2SO_4 treatment is more effective for the improvement of the fibers' properties.After HCISO_3 treatment for 2 h,the fibers' strength and electrical conductivity reach up to-2 GPa and-4.3 MS/m,which are promoted by-200%and almost one order of magnitude than those without acid treatment,respectively.The load-bearing status of the CNT fibers are analyzed based on the downshifts of the G' band and the strain transfer factor of the fibers under tension.The results reveal that acid treatment could greatly enhance the load transfer and inter-bundle strength.With the HCISO3 treatment,the strain transfer factor is enhanced from-3.9%to-53.6%.展开更多
In this work,Yb2O3 and Mg O were used as sintering aids in preparing silicon nitride ceramics by gas pressure sintering( 0. 6 MPa N2atmosphere) to investigate how the amounts of Yb2O3- Mg O influence the mechanical ...In this work,Yb2O3 and Mg O were used as sintering aids in preparing silicon nitride ceramics by gas pressure sintering( 0. 6 MPa N2atmosphere) to investigate how the amounts of Yb2O3- Mg O influence the mechanical properties and thermal conductivity of silicon nitride ceramics. The total contents of Yb2O3- Mg O added were 1 mol%,2 mol%,4 mol%,6 mol%,8 mol%,10 mol%,12 mol%,14 mol%,keeping the Yb2O3-Mg O molar ratio of 1 ∶ 1 steadily. Curves of the relative density,thermal conductivity and bending strength plotted against the aids content present a ‘mountain'shape with a maximum at nearly 10 mol% aids. The fracture toughness increased with the amounts of additives up to10 mol% and decreased slightly thereafter. The mechanical properties and thermal conductivity were almost proportional to the amount of the additives before10 mol%. When the content of aids exceeded 10 mol%,it would weaken the mechanical properties and thermal conductivity of the ceramics. The optimum content of Yb2O3- Mg O was 10 mol% by gas pressure sintering( 0. 6MPa) at 1 850 ℃ for 4 h,which led to a relative density of 98. 9%,a flexural strength of( 966 ± 38)MPa as well as a fracture toughness of( 6. 29 ± 0. 29)MPa·m1 /2and thermal conductivity of 82 W /( m·K).展开更多
文摘ITO thin films were grown on PC(polycarbonate), PMMA(polymethyl methacrylate) and glass substrates by r.f. magnetron sputtering. The electrical, structural and chemical characteristics of ITO films were analyzed by the Hall Technique, X-ray diffraction, and X-ray photoelectron spectroscopy. XPS studies suggest that all the ITO films consist of crystalline and amorphous phases. The degree of crystallinity increases from less than 45% to more than 90% when the substrate temperature increases from 80 to 300 ℃. The In and Sn exist in the chemical state of In^3+ and Sn^4+, respectively, independent of substrate type and temperature. The enrichment of Sn on surface and In in body of ITO films are also revealed. And, the oxygen deficient regions exist both in surface layer and film body. For ITO films deposited under 180 ℃ , the carrier concentration are mainly provided by oxygen vacancies, and the dominant electron carrier scattering mechanism is grain boundary scattering between the crystal and the amorphous grain. For ITO films deposited over 180 ℃, the carrier concentration are provided by tin doping, and the dominant scattering mechanism transforms from grain boundary scattering between the crystal grains to ionized impurity scattering with increasing deposition temperature.
基金supported by the National Natural Science Foundation of China(Grant No.61171017)
文摘Nano-scale titanium oxide memristors exhibit complex conductive characteristics, which have already been proved by existing research. One possible reason for this is that more than one mechanism exists, and together they codetermine the conductive behaviors of the memristor. In this paper, we first analyze the theoretical base and conductive process of a memristor, and then propose a compatible circuit model to discuss and simulate the coexistence of the dopant drift and tunnel barrier-based mechanisms. Simulation results are given and compared with the published experimental data to prove the possibility of the coexistence. This work provides a practical model and some suggestions for studying the conductive mechanisms of memristors.
基金This work was supported by the National Natural Science Foundation of China (Grant No: 19875050, 10075041, 10075044).
文摘The microstructure and conductive mechanism of high density polyethylene/carbon black (HDPE/CB) composite were investigated by positron annihilation lifetime spectroscopy (PALS). The PALS were measured in two series of samples, one with various CB contents in the composites and the other with various gamma-irradiation doses in HDPE/CB composite containing 20 wt% CB. It was found that CB particles distribute in the amorphous regions, the CB critical content value in HDPE/CB composite is about 16.7 wt% and the suitable gamma-irradiation dose for improving the conductive behavior of HDPE/CB composite is about 20 Mrad. The result observed for the second set of samples suggests that gamma-irradiation causes not only cross-linking in amorphous regions but also destruction of the partial crystalline structure. Therefore, a suitable irradiation dose, about 20 Mrad, can induce sufficient cross-linking in the amorphous regions without enhancing the decomposition of crystalline structure, so that the positive temperature coefficient (PTC) effect remains while the negative temperature coefficient (NTC) effect is suppressed. A new interpretation of the conductive mechanism, which might provide a more detailed explanation of the PTC effect and the NTC effect has been proposed.
文摘Transparent conducting F-doped texture SnO2 films with resistivity as low as 5× 10-4 Ω ·cm,with carrier concentrations between 3.5 × 1020 and 7× 1020 cm-3 and Hall mobilities from 15.7 to 20.1 cm2/(V/s) have been prepared by atmosphere pressure chemical vapour deposition (APCVD). These polycrystalline films possess a variable preferred orientation, the polycrystallite sizes and orientations vary with substrate temperature. The substrate temperature and fluorine flow rate dependence of conductivity, Hall mobility and carrier conentration fOr the resultingfilms have been obtained. The temperature dependence of the mobiity and carrier concentrationhave been measured over a temperature range 16~400 K. A systematically theoretical analysis on scattering mechanisms for the highly conductive SnO2 films has been given. Both theoretical analysis and experimental results indicate that for these degenerate, polycrystalline SnO2 :F films in the low temperature range (below 100 K), ionized impurity scattering is main scattering mechanism. However, when the temperature is higher than 100 K, the lattice vibration scattering becomes dominant. The grain boundary scattering makes a small contribution to limit the mobility of the films.
文摘The conductivity of non-crystalline fast ionic conductor for B_2O_3-Li_2O-LiCl-Al_2O_3 system is studiedin this paper. The glass structure of this system is discussed by means of infrared spectrum and X-ray fluorescence analysis, and the effects of LiCl and A1_2O_3 on the conductivity of Li^+ in the system are studied as well. Adding Li_2O to the system gives rise to transfer from [BO_3] triangular units to [BO_4] tetrahedral. When Li_2O content exceeds 30mol%, the main group of the glass is the diborate group with more [BO_4] tetrahedra. The adding of LiCl has no obvious influence on the glass structure, and LiCl is under a state dissociated by network, but with the increase of LiCl, the increase of conductivity is obvious. By adding A1_2O_3, the glass can be formed when the room-temperature is cooling down,the conductivity decreases while the conductive activatory energy increases for the glass. The experiment shows that conductivity in the room-temperature is σ= 6.2×10^(-6)Ω^(-1)cm^(-1), when at 300℃, the σ=6.8×10^(-3)Ω^(-1)cm^(-1). The conductive activatory energy computed is 0.6~1.0eV.
文摘Na_(5+x) YAl_x Si_(4-x) O_(12) polycrystalline solid electrolytes are prepared by solid reactions. By the analyses of X-ray, TG and DTA, infrared spectu re, and SEM, the variasion of their density with the composition X are discussed Their electric conductivity in the temperature range of R. T. to 300℃ are determined with electric brigde, and their variasions with the compositions X and temperature are studied. Their activations in the tem- perature range 140℃ to 300℃ are calculated, and their variation with the compositons X are discussed.
文摘High thermal conductivity dense silica bricks have the higher thermal conductivity than ordinary silica bricks,which is conducive to the realization of energy saving and emission reduction in the iron and steel industry.The performance of ordinary silica bricks and high thermal conductivity dense silica bricks was compared,and the high thermal conductivity mechanism was analyzed.The results show that(1)compared with ordinary silica bricks,high thermal conductivity dense silica bricks have the characteristics of higher thermal conductivity,lower apparent porosity,higher tridymite content,higher compressive strength,and higher thermal expansion;(2)by increasing the tridymite content and reducing the porosity,the close packing of honeycombα-tridymite improves the density and continuity of the SiO_(2)frame structure of the silica bricks,and the larger area perpendicular to the heat transfer direction improves the thermal conductivity of the bricks;(3)the densification of the silica bricks also increases the thermal expansion of the bricks,but they still meet the standard requirements.
基金Project supported by the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(CAS)(Grant No.XDB 18010401)the Key Research Program of Frontier Sciences of CAS(Grant No.QYZDB-SSW-DQC009)+2 种基金the“135”Program of the Institute of Geochemistry of CASthe Hundred-Talent Program of CASthe National Natural Science Foundation of China(Grant Nos.41474078,41774099,and 41772042)
文摘The electrical conductivities of single-crystal K-feldspar along three different crystallographic directions are investigated by the Solartron-1260 Impedance/Gain-phase analyzer at 873 K–1223 K and 1.0 GPa–3.0 GPa in a frequency range of 10-1 Hz–106 Hz. The measured electrical conductivity along the ⊥ [001] axis direction decreases with increasing pressure, and the activation energy and activation volume of charge carriers are determined to be 1.04 ± 0.06 e V and 2.51 ± 0.19 cm~3/mole, respectively. The electrical conductivity of K-feldspar is highly anisotropic, and its value along the⊥ [001] axis is approximately three times higher than that along the ⊥ [100] axis. At 2.0 GPa, the diffusion coefficient of ionic potassium is obtained from the electrical conductivity data using the Nernst–Einstein equation. The measured electrical conductivity and calculated diffusion coefficient of potassium suggest that the main conduction mechanism is of ionic conduction, therefore the dominant charge carrier is transferred between normal lattice potassium positions and adjacent interstitial sites along the thermally activated electric field.
基金financial support from the National Natural Science Foundation of China(21978024)the Beijing Natural Science Foundation(2202034)。
文摘To attain the objectives of carbon peaking and carbon neutrality,the development of stable and highperformance ion-conducting materials holds enormous relevance in various energy storage and conversion devices.Particularly,crystalline porous materials possessing built-in ordered nanochannels exhibit remarkable superiority in comprehending the ion transfer mechanisms with precision.In this regard,covalent organic frameworks(COFs)are highly regarded as a promising alternative due to their preeminent structural tunability,accessible well-defined pores,and excellent thermal/chemical stability under hydrous/anhydrous conditions.By the availability of organic units and the diversity of topologies and connections,advances in COFs have been increasing rapidly over the last decade and they have emerged as a new field of proton-conducting materials.Therefore,a comprehensive summary and discussion are urgently needed to provide an"at a glance"understanding of the prospects and challenges in the development of proton-conducting COFs.In this review,we target a comprehensive review of COFs in the field of proton conductivity from the aspects of design strategies,the proton conducting mechanism/features,the relationships of structure-function,and the application of research.The relevant content of theoretical simulation,advanced structural characterizations,prospects,and challenges are also presented elaborately and critically.More importantly,we sincerely hope that this progress report will form a consistent view of this field and provide inspiration for future research.
基金supported by the National Natural Science Foundation of China(12102068 and 11832007)Shaoxiong Xie acknowledges the support of JSPS International Research Fellowship(P21704).
文摘With the rapid development of high-end industries,the demand for high-temperature piezoelectric materials is significantly increasing.However,realizing the ultra-high performance to meet more ap-plications still faces major scientific and engineering challenges of our time.Here,a new Nb/Mn co-doped CaBi_(4)Ti_(4)O_(15)(CBT)high-temperature piezoelectric material system of CaBi_(4)Ti_(4-x)(Nb_(2/3)Mn_(1/3))_(x)O_(15)was synthesized by the conventional solid-state sintering method.The results show that the addition of the dopants tends to break the long-range ferroelectric chain and soften the flexibility of polarization,resulting in more distorted crystal structure and better ferroelectric properties of CBT ceramics.The ultra-high piezoelectric constant(d_(33)=26.8 pC/N)is thus attained in CBT-based ceramics with x=0.12,which is about several times larger than that of pure CBT ceramics.Moreover,numerous nano-sized layered domain structures that lie on the lateral plane of grains are observed in ceramics,with lower domain wall energy and better dynamic features under electric fields,mainly responsible for the origin of enhanced performance.Besides,excess dopants could make the conductivity mechanism of CBT ceramics transform from p-type to n-type,and also result in a shift of conduction relaxation mechanism from defect dipole rotation polarization to electron relaxation polarization.The work not only provides a promising candidate for high-temperature piezoelectric materials,but also opens a window for opti-mizing performance by tailoring domain structures using chemical modification.
基金National Natural Science Foundation of China(51773169 and 51973173)Guangdong Basic and Applied Basic Research Foundation(2019B1515120093)+2 种基金Technological Base Scientific Research ProjectsNatural Science Basic Research Plan for Distinguished Young Scholars in Shaanxi Province(2019JC-11)Polymer Electromagnetic Functional Materials Innovation Team of Shaanxi Sanqin Scholars.
文摘Rapid development of energy,electrical and electronic technologies has put forward higher requirements for the thermal conductivities of polymers and their composites.However,the thermal conductivity coefficient(λ)values of prepared thermally conductive polymer composites are still difficult to achieve expectations,which has become the bottleneck in the fields of thermally conductive polymer composites.Aimed at that,based on the accumulation of the previous research works by related researchers and our research group,this paper proposes three possible directions for breaking through the bottlenecks:(1)preparing and synthesizing intrinsically thermally conductive polymers,(2)reducing the interfacial thermal resistance in thermally conductive polymer composites,and(3)establishing suitable thermal conduction models and studying inner thermal conduction mechanism to guide experimental optimization.Also,the future development trends of the three above-mentioned directions are foreseen,hoping to provide certain basis and guidance for the preparation,researches and development of thermally conductive polymers and their composites.
文摘BN ceramic is an advanced engineering ceramics with excellent thermal shock resistance, good workability and excellent dielectricity.TiB 2 ceramic has excellent electric conductivity,high melting points, and corrosion resistance to molten metal.Therefore,the composite consisting of BN and TiB 2 ceramics is expected to have a combination of above mentioned properties,thereby can be used as self heating crucible.In this paper,hot pressing technology was used to fabricate the high performance BN TiB 2 composite materials.microstructure and electric conducting mechanism were studied,and the relationship between the microstructure and physical property was discussed.The results show that the microstructure of composites has a great influence on the physical property of composites.The BN TiB 2 composites with excellent mechanical strength and stable resistivity can be obtained by optimizing the processing parameter and controlling the microstructure of composites.
文摘In view of the fact that safety production supervision of coal mines in China features low efficacy, this paper applies principles of cybernetics to simulate the dynamic process of safety supervision, and proposes that institutional variables be controlled to support intermediate goals, which in turn contribute to the ultimate safety production objective. Rather than focusing all attention on safety issues of working faces, supervising departments of coalmines are advised to pay much more attention to institutional factors that may impact people’s attitude and behavior, which are responsible for most coalmine accidents. It is believed that such a shift of attention can effectively reduce coalmining production accidents and greatly enhance supervision efficacy.
基金The authors acknowledge the financial support from National Natural Science Foundation of China(No.51772127,51772131,and 51802119)Taishan Scholars(No.ts201712050)+2 种基金Major Program of Shandong Province Natural Science Foundation(ZR2018ZB0317)Natural Science Doctoral Foundation of Shandong Province(ZR2018BEM018,ZR2019BB057)Collaborative Innovation Center of Technology and Equipment for Biological Diagnosis and Therapy in Universities of Shandong.
文摘Metal-organic frameworks(MOFs),typically constructed with metallic nodes and organic linkers,have influenced the development of modular solid materials.Their adjustable molecular structure provides a remarkable variety of MOF-based solid-state structures towards diverse applications.However,the low conductivity of traditional MOFs extremely hinders their applications in electronic and electrochemical devices.The emerging conductive MOFs,generally possessing twodimensional layered structures,are endowed with both the structural merits of common MOFs and exceptional electronic/ionic conductivities.Besides,the selection and optimization of ligands and metal centers,as well as synthetic methods enormously affects the intrinsic conductivity of conductive MOFs.The distinctive crystal structures and superb conductivity promise their appealing applications in electrochemical energy-related fields.In the review,we mainly summarize representative crystal features,conducting mechanisms and recent advances in rational design and synthesis of conductive MOFs,along with their versatile applications as electrodes for electrochemical capacitors and rechargeable batteries,and as catalysts towards electrocatalysis.Finally,the involved challenges and future trends/prospects of the conductive MOFs for electrochemical energyrelated applications are further proposed.
基金the Scientific Grant Agency VEGA, Slovak Republic (1/2100/05 and 1/0173/08)
文摘Relations between the structure, ionic conductivity and dielectric properties of fluoride systems of different structures containing rare earth elements were presented. Superionic conductivities, by fluoride ions, of fluorite-structured (MF2-REF3, M=Ba, Pb, RE=La-Lu, Sc, Y), orthorhombic (REF3, RE=Tb-Er, Y), tysonite-structured (REF3-MF2, RE=La-Nd, M=Sr), monoclinic (BaRE2Fs, RE=Ho-Yb, Y) fluoride single crystals and eutectic composites (LiF-REF3, RE=La-Gd, Y) were compared. Anisotropy of electrical properties of crystals with a lower symmetry was explained by modeling optimum ionic paths. For explanation of concentration dependences of fast ionic conductivity, models of aggregation of defects into clusters were proposed. In fluorite-structured crystals, the highest ionic conductivity was found for PbF2:7 mol% ScF3 (at 500 K, σ500=0.13 S/cm). In tysonite-structured crystals, the highest ionic conductivity was found for LaF3:3 mol% SrF2 (σ500=2.4×10^-2 S/cm). Different types of coordination polyhedrons and their different linking in orthorhombic and tysonite structure explained large differences between conductivities in both structures. Eutectic systems, prepared as directionally solidified composites, enabled to study some orthorhombic fluoride phases (GdF3, SmF3), which cannot be prepared as single crystals. An influence of the orthorhombic-tysonite phase transition on the ionic conductivity was shown.
文摘A new glass system (Bi2O3)50(Fe2O3)10(Li2O)x(K2O)40-x, where x changes in steps of 5 mole fraction between 0 and 40, was selected to study the electrical relaxation and the mixed alkali effect (MAE) phenomena. Measurements of ac conductivity σac, dielectric permittivity ε′ and loss factor tanδ in the frequency range of 0.12~10^2 kHz and in the temperature range of 300~650 K were carried out. The temperature dependence of the ac conductivity shows a slow increasing rate at low temperature and high frequency and a rapid increase at high temperature and low frequency. At constant temperature, the ac conductivity is found to be proportional to ω^8, where s is the frequency exponent, which is less than 1. Analysis of the conductivity data and the frequency exponent shows that the overlapping large polaron tunnelling (OLPT) model of ions is the most favorable mechanism for the ac conduction in the present glass system. The ac response, the dc conductivity and dielectric relaxation have the same activation energy and they originate from the same basic transport mechanism. The results of the dielectric permittivity show no maximum peak in the temperature and frequency range studied. This absence of maximum peak is an indication of non-ferroelectric behavior of all the studied samples. The MAE has been detected in the ac conductivity, which is the same as the classical MAE in the dc conductivity. The electrical parameters such as dielectric permittivity ε′ and real dielectric modulus M′ show a typical minimum deviation from linearity by about two orders of magnitude. The loss factor tanδ and the imaginary dielectric modulus M″ are insignificantly dependent on composition even at the same transition temperature Tg.
基金supported by the National High-Tech Research and Development Program of China (No.2009AA03Z116)the National Natural Science Foundation of China (No.50971020)
文摘To extend the application of carbon nanotubes (CNTs) and explore novel aluminum matrix composites,CNTs were coated by molybdenum layers using metal organic chemical vapor deposition,and then Mo-coated CNT (Mo-CNT)/Al composites were prepared by the combination processes of powder mixing and spark plasma sintering.The influences of powder mixing and Mo-CNT content on the mechanical properties and electrical conductivity of the composites were investigated.The results show that magnetic stirring is better than mechanical milling for mixing the Mo-CNTs and Al powders.The electrical conductivity of the composites decreases with increasing Mo-CNT content.When the Mo-CNT content is 0.5wt%,the tensile strength and hardness of Mo-CNT/Al reach their maximum values.The tensile strength of 0.5wt% Mo-CNT/Al increases by 29.9%,while the electrical conductivity only decreases by 7.1%,relative to sintered pure Al.The phase analysis of Mo-CNT/Al composites reveals that there is no formation of Al carbide in the composites.
基金Supported by the National Natural Science Foundation of China
文摘The deformation potential theory for one-dimensional organic polymer is studied. This approximation is then used to calculate the mobilities of carriers and the conductivity of trans-polymonocyanoacetylene (PMCA). The results of calculations are in fairly good agreement with experimental data.
基金Project supported by the National Basic Research Program of China(Grant No.2012CB932302)the National Natural Science Foundation of China(Grant Nos.11634014,51172271,51372269,and 51472264)the“Strategic Priority Research Program”of the Chinese Academy of Sciences(Grant No.XDA09040202)
文摘Continuous CNT fibers have been directly fabricated in a speed of 50 m/h-400 m/h,based on an improved chemical vapor deposition method.As-prepared fibers are further post-treated by acid.According to the SEM images and Raman spectra,the acid treatment results in the compaction and surface modification of the CNTs in fibers,which are beneficial for the electron and load transfer.Compared to the HNO3 treatment,HClSO_3 or H_2SO_4 treatment is more effective for the improvement of the fibers' properties.After HCISO_3 treatment for 2 h,the fibers' strength and electrical conductivity reach up to-2 GPa and-4.3 MS/m,which are promoted by-200%and almost one order of magnitude than those without acid treatment,respectively.The load-bearing status of the CNT fibers are analyzed based on the downshifts of the G' band and the strain transfer factor of the fibers under tension.The results reveal that acid treatment could greatly enhance the load transfer and inter-bundle strength.With the HCISO3 treatment,the strain transfer factor is enhanced from-3.9%to-53.6%.
文摘In this work,Yb2O3 and Mg O were used as sintering aids in preparing silicon nitride ceramics by gas pressure sintering( 0. 6 MPa N2atmosphere) to investigate how the amounts of Yb2O3- Mg O influence the mechanical properties and thermal conductivity of silicon nitride ceramics. The total contents of Yb2O3- Mg O added were 1 mol%,2 mol%,4 mol%,6 mol%,8 mol%,10 mol%,12 mol%,14 mol%,keeping the Yb2O3-Mg O molar ratio of 1 ∶ 1 steadily. Curves of the relative density,thermal conductivity and bending strength plotted against the aids content present a ‘mountain'shape with a maximum at nearly 10 mol% aids. The fracture toughness increased with the amounts of additives up to10 mol% and decreased slightly thereafter. The mechanical properties and thermal conductivity were almost proportional to the amount of the additives before10 mol%. When the content of aids exceeded 10 mol%,it would weaken the mechanical properties and thermal conductivity of the ceramics. The optimum content of Yb2O3- Mg O was 10 mol% by gas pressure sintering( 0. 6MPa) at 1 850 ℃ for 4 h,which led to a relative density of 98. 9%,a flexural strength of( 966 ± 38)MPa as well as a fracture toughness of( 6. 29 ± 0. 29)MPa·m1 /2and thermal conductivity of 82 W /( m·K).