Y2O3稳定ZrO2材料的电导活化能

在313～473K温度范围内测定了一种Y2O3稳定ZrO2材料(YSZ)的交流电导率谱,进而导出了材料的直流电导率并分析了其随温度的变化关系.研究发现:在低温下材料的电导活化能随温度的升高而增大.这一实验现象与在高温下所观察到的活化能随温度升高而降低的规律截然相反.通过分析材料中氧空位的解缔及迁移机制,对YSZ材料中电导活化能随温度的变化关系作出了一个合理的解释.     

La0.6Sr0.4Co1-yFeyO3的混合导电性研究

采用直流四探针法和两端子电子阻塞电极交流阻抗谱研究了GNP法制备La0．6Sr0．4Co1-yFeyO3陶瓷的电子-离子混合导电性能．在室温-900℃范围内，La0．6Sr0．4CoO3的电子电导率随温度的升高而单调降低，其它样品的电子电导率随温度的升高在600℃附近达到最大值．La0．6Sr0．4Co1-yFeyO3陶瓷的氧离子电导率随温度的升高而增加．在相同温度下，随着Co／Fe比例的增加，La0．6Sr0．4Co1-yFeyO3陶瓷的电子电导率和氧离子电导率增加，电子导电活化能和离子导电活化能降低．氧离子迁移数随温度的升高而增加，随Co／Fe比例的增加而降低．     

ZnO-MgO-P2O5磷酸盐玻璃酸溶机理研究

采用表面失重法分析40ZnO-10MgO-50P2O5玻璃在酸性溶液中的溶解过程.实验结果表明:含二价金属阳离子的磷酸盐玻璃在水中溶解速度缓慢,但在酸性溶液中,因R2 和H 离子交换加速,破坏了结构的稳定性,磷氧基团很容易发生水解,在pH＜3时,玻璃的溶解速率会急剧增大.溶解速率随温度升高呈现指数增加的趋势,溶解活化能随pH值的升高而降低;在高浓度盐酸溶液中,溶解速率随浓度变化出现极值,这一切均应归于H 和H2O活度的双重作用;通过对失重曲线变化的研究发现:玻璃的溶解过程分为两个阶段,第一阶段失重量与时间平方根成正比,第二阶段失重量与时间成正比,说明玻璃表面的水化层经历了形成、发展和稳定的过程.     

Cr2O3的添加对MgO-Al2O3-SiO2-TiO2系统微晶玻璃析晶行为的影响

利用DTA、XRD、SEM和TEM等实验手段,研究了Cr2O3的添加对于MgO-Al2O3-SiO2-TiO2系统微晶玻璃析晶行为的影响.同时,通过Ozawa和Kissinger方法计算出系统中α-堇青石的析晶活化能E.研究结果表明,少量Cr2O3的添加并不改变MgO-Al2O3-SiO2-TiO2系统玻璃析出的晶相类型,但是提高了玻璃转化温度Tg,降低了α-堇青石的析晶活化能.由于析晶活化能的降低,促进了α-堇青石的析出,最终获得了一种有实用价值的微波介质材料.该材料在微波频率下(10GHz)的相对介电常数约5.5,介电损耗＜7×10-4.     

电解质与电极界面产物电导率测试与研究

为研究氧化钇稳定氧化锆（YSZ）电解质材料与La1-xMxNiO3（M=Ca、Sr、Mg）电极材料界面反应物的电输运特性,采用二端法测试样品直流电导率和交流电导率。结果表明：样品的直流电导率、交流电导率均随温度的升高而增加,交流电导率在低频区基本不变,在高频区随频率增大而增大,解释了电极的电输运性能,综合比较掺杂Ca的样品性能比较优良。     

Al2O3掺杂对YSZ固体电解质烧结及电性能的影响

研究了用常规共沉淀法掺杂Al2O3对YSZ固体电解质的烧结及电性能的影响．结果表明：适量的Al2O3能提高YSZ材料的烧结性能，促使其致密化，但过量的Al2O3对材料的致密化不利；同时，材料的晶界电导随Al2O3含量的增大表现出先增大后减小的变化趋势，这与Al2O3对YSZ晶界两方面的不同影响有关，Al2O3偏析于晶界一方面能清除晶界上对氧离子电导不利的SiO2，但另一方面也会降低晶界空间电荷层中的自由氧离子空穴的浓度．     

沉积温度对Gd掺杂CeO2电解质薄膜生长及电学特性的影响

采用反应射频磁控溅射技术,在非晶石英衬底上不同温度下制备了纳米多晶Gd掺杂CeO2(简称GDC)氧离子导体电解质薄膜,采用X射线衍射仪、原子力显微镜对薄膜物相、晶粒大小、生长形貌进行了表征,利用交流阻抗谱仪测试了GDC薄膜的电学性能.结果表明,GDC薄膜生长取向随沉积温度而变化:300-400℃时为强(111)织构生长,而500-600℃时薄膜趋于无规则生长;随着沉积温度的升高,薄膜的牛长形貌由同一取向的大棱形生长岛转变为密集球形小生长岛;GDC多晶薄膜的电导活化能约为1.3eV,接近于晶界电导活化能值,说明GDC交流阻抗主要源于晶界的贡献;晶界空间电荷效应导致GDC薄膜电导率随晶粒尺寸而变化,晶粒尺寸越小,电导率越大.     

水热法合成纳米SnO2粉体

以硝酸锡为原料，配成稳定溶液，进行水热反应合成得到了晶粒尺寸只有数纳米的SnO2粉体．以FT—IR，XRD，TEM等分析手段对粉体进行了表征．FT—IR表明所得粉体均已实现了晶化．XRD衍射峰显示为SnO2相，衍射峰宽化明显，且随水热温度的升高宽化变窄，结晶性提高．粉体的晶胞体积随水热温度也呈现规律性变化．TEM表明粒子均为数纳米，粉体的分散性能良好，团聚很少。     

ZrB2/C复合材料的性能及微观结构研究

采用热压工艺制备了ZrB2／C复合材料，考察了ZrB2掺杂量对材料抗弯强度、热导率、电阻率的影响以及微观结构的变化．结果表明：随ZrB2含量增加，材料抗弯强度和热导率不断升高，在掺杂量为10％时，抗弯强度达到最大值131MPa，热导率达到161W／m．K的最大值，此后，抗弯强度和热导率随掺杂量增加而降低．然而，材料的电阻率随ZrB。含量的增加不断下降．微观结构分析表明，随着ZrB2掺杂量增加，材料的石墨化度和微晶尺寸增大，晶面层间距减小．材料的微观结构强烈地影响着材料的力学、导电、导热等宏观性能．     

TiO2对CaO-MgO-P2O5-SiO2系玻璃晶化影响的研究

CaO-MgO-P2O5-SiO2系微晶玻璃是一种新型医学生物材料，该材料洋仅具有良好的生物相溶性，还具有一定的力学性能，本文采用热热分析（DTA）方法对以TiO2作为晶核剂的该系生物微晶玻璃的析晶动力学参数进行了测定，所得数据经计算机拟合后，其结果表明，在一定范围内引入TiO2（≤8.7wt%)能降低该系玻璃的析晶活化能E，有促进玻璃析晶的作用，当TiO2含量达到8.7wt%时，E达到最小值，当TiO2含量＞8.7wt%时，E值反而回升，晶化指数n与该玻璃体系中加入TiO2的变化规律与E值随TiO2的变化规律是一致的。     

Conductivity and dielectric studies on (Na0·4Ag0·6)2PbP2O7 compound

Electrical properties of the (Na_0·4Ag_0·6)₂PbP₂O₇ compound were studied using complex impedance spectroscopy in the frequency range 200 Hz–5 MHz and temperature range (484–593 K). Combined impedance and modulus plots were used to analyse the sample behaviour as a function of frequency at different temperatures. Temperature dependence of d.c. and a.c. conductivity indicates that electrical conduction in the material is a thermally activated process. The frequency dependence of the a.c. conduction activation energy was found to obey a mathematical formula.     

Low-field D. C. conductivity in the bulk amorphous GexTe10Se90-x System

D. C. conductivity measurements have been made as a function of temperature and electric field on bulk amorphous Ge_xTe₁₀Se_90?x (10? x ?40) samples, in order to identify the conduction mechanism and to study the effect of the electric field on the conductivity. In the entire range of temperature (80–300 K) the conduction in all the samples is found to take place $\text{via}$ thermally assisted tunnelling of the charge carriers in the localized states of the band tails. The addition of germanium results in an increase in the localized state density and hence an increase in conductivity. An increase in the electric field decreases the activation energy, thereby increasing the conductivity of the samples. The conductivity shows an exponential dependence on the electric field.     

Dielectric anomaly in LiCa2V5O15 ceramics

A polycrystalline sample of LiCa₂V₅O₁₅ (LCV) was prepared using a mixed oxide method at low temperature (i.e., at 630 °C). X-ray structural analysis shows the single-phase formation of the compound in the orthorhombic crystal system at room temperature. A study on the surface morphology of the compound showed uniform grain distribution on the surface and in the bulk of the sample with less porosity. A dielectric anomaly suggests that the compound has a transition temperature at 274 °C. The activation energy, calculated from the temperature dependence of ac conductivity (dielectric data), of the compound was found to be 0.67 eV at 10 kHz. The nature of the variation of conductivity and value of activation energy in different regions, suggest that the conduction process is of mixed type (i.e., ionic-polaronic and space charge generated from the oxygen ion vacancies).     

Crystal structure, thermal expansion and electrical conductivity of Nd0.7Sr0.3Fe1−xCoxO3 (0≤x≤0.8)

The crystal structure, thermal expansion and electrical conductivity of the solid solution Nd_0.7Sr_0.3Fe_1−xCo_xO₃ for 0≤x≤0.8 were investigated. All compositions had the GdFeO₃-type orthorhombic perovskite structure. The lattice parameters were determined at room temperature by X-ray powder diffraction (XRPD). The pseudo-cubic lattice constant decreased continuously with x. The average linear thermal expansion coefficient (TEC) in the temperature range from 573 to 973 K was found to increase with x. The thermal expansion curves for all values of x displayed rapid increase in slope at high temperatures. The electrical conductivity increased with x for the entire temperature range of measurement. The calculated activation energy values indicate that electrical conduction takes place primarily by the small polaron hopping mechanism. The charge compensation for the divalent ion on the A-site is provided by the formation of Fe⁴⁺ ions on the B-site (in preference to Co⁴⁺ ions) and vacancies on the oxygen sublattice for low values of x. The large increase in the conductivity with x in the range from 0.6 to 0.8 is attributed to the substitution of Fe⁴⁺ ions by Co⁴⁺ ions. The Fe site has a lower small polaron site energy than Co and hence behaves like a carrier trap, thereby drastically reducing the conductivity. The non-linear behaviour in the dependence of log σT with reciprocal temperature can be attributed to the generation of additional charge carriers with increasing temperature by the charge disproportionation of Co³⁺ ions.     

Transport Properties of K_xV_2O_5·nH_2O Nanocrystalline Films

Five different compositions of K x V 2 O 5 ·nH 2 O(where x=0.00,0.0017,0.0049,0.0064 and 0.0091 mol) were prepared by the sol-gel process.Electrical conductivity and thermoelectric power were measured parallel to the substrate surface in the temperature range of 300-480 K.The electrical conductivity showed that all samples were semiconductors and that conductivity increased with increasing K content.The conductivity of the present system was primarily determined by hopping carrier mobility.The carrier density was evaluated as well.The conduction was confirmed to obey non-adiabatic small polaron hopping.The thermoelectric power or Seebeck effect,increased with increasing K ions content.The results obtained indicated that an n-type semiconducting behavior within the temperature range was investigated.     

Dielectric relaxation related to single-ionized oxygen vacancies in (Pb1−xLax)(Zr0.90Ti0.10)1−x/4O3 ceramics

The dielectric relaxation phenomenon has been studied in lanthanum modified lead zirconate titanate ceramics in the high temperature paraelectric phase. The high temperature dielectric response revealed an anomalous behavior, which is characterized by an increase of the real component of the dielectric permittivity with the increase of the temperature. At the same time, a similar behavior, with very high values, has been observed in the imaginary component of the dielectric permittivity, which can be associated with conduction effects related to the conductivity losses. The frequency and temperature behavior of the complex dielectric permittivity has been analyzed considering the semi-empirical complex Cole-Cole equation. The activation energy value, obtained from the Arrhenius’ dependence for the relaxation time, was found to decreases with the increase of the lanthanum concentration and has been associated with single-ionized oxygen vacancies. The short-range hopping of oxygen vacancies is discussed as the main cause of the dielectric relaxation.     

Impurity band in in-doped CdCr2Se4 observed in the spectral dependence of the photoconductance

The spectral dependence of the photoconductance of In-doped CdCr₂Se₄ crystals was measured in the photon energy range from 0.2 eV to 2.5 eV. At a temperature of 80 K, i.e. below the Curie temperature of 132 K, two peaks of the impurity photoconductivity are observed. The peak energy of 0.38 eV agrees with the thermal activation energy determined from the slope of the ? vs T curves at higher temperatures. This agreement is an experimental evidence for the impurity band formed by the In donors and the Se vacancy donors which should be responsible for the large negative magnetoresistance due to “magnetic impurity states” in these crystals. At a temperature of 155 K, i.e. above the Curie temperature, the structure of the photoconductance vanishes due to the thermal activation of electrons from occupied donor levels to the conduction band.     

Porous yttria-stabilized zirconia ceramics with ultra-low thermal conductivity. Part II: temperature dependence of thermophysical properties

This study describes the experimental results of thermal diffusivity, specific heat at constant pressure, and thermal conductivity of porous 8 mol% yttria-stabilized zirconia (YSZ) ceramics in a temperature range from room temperature to 1,400 °C. It is a follow-up study of the earlier report titled by “Porous YSZ ceramics with ultra-low thermal conductivity”, which focused on the room-temperature thermal conductivity. The thermal diffusivity of porous YSZ ceramics decreased with the increase of the measurement temperature up to 600–1,000 °C, followed by an increasing trend with increasing temperature. The specific heat did not exhibit any significant dependence on sintering temperature and agreed with literature data. The thermal conductivity of the porous YSZ ceramics showed an insensitive tendency of change with measurement temperature. The thermal conductivity fell in groups by the sintering temperature level. This investigation also discussed an appropriate sintering temperature of porous YSZ ceramics, which had both low thermal conductivity and high strength required by the practical service.     

Electrical properties of crystalline PbxSn1−xTe0.5Se0.5 thin films

Electrical conductivity in the dark, σ, and thermoelectric power, S, of Pb_xSn_1−xTe_0.5Se_0.5 films with x = 0.4, 0.6, 0.8, and 1 were studied for films annealed at 473 K in the temperature range 300-473 K, while the Hall voltage was investigated at room temperature. The temperature dependence of σ revealed an intrinsic conduction mechanism above 370 K, while for temperatures less than 370 K an extrinsic conduction is dominant. Both activation energy, ΔE₁, and the energy gap, E_g, were found to decrease with increasing Sn content. This decrease of E_g with increasing Sn content revealed that band inversion exists. The variation of S with temperature revealed that the investigated samples are non-degenerate semiconductors with p-type conduction. Also, the Fermi energy, E_F, was determined from the linear variation of S with 1/T in the intrinsic range. The compositional dependence of the room temperature Hall constant, R_H (0.21-0.38 cm³/Coul.), hole carrier's concentration, p (2.9-1.6 × 10¹⁹ cm⁻³), Hall mobility, μ_H (0.88-0.03 cm²/V s), and effective mass, m^∗/m_e (0.28-0.78) are given.     

Characterization of FeS2-pyrite thin films synthesized by sulphuration of amorphous iron oxide films pre-deposited by spray pyrolysis

FeS₂-thin films with good crystallinity were synthesized by a simple method which consists of sulphuration, under vacuum, of amorphous iron oxide thin films pre-deposited by spray pyrolysis of FeCl₃·6H₂O (0.03 M)-based aqueous solution onto glass substrates heated at 350 °C. At optimum sulphuration temperature (450 °C) and duration (6 h), black green layers having granular structure and high absorption coefficient (5.10⁴ cm⁻¹) were obtained. The study of the electrical properties of the as-prepared films vs. the temperature variations showed three temperature domain dependence of the conductivity behaviour. The first one corresponds to the high temperature range (330 K–550 K) for which an Arrhenius plot type was obtained. The activation energy value was estimated at about 61.47 meV. The second domain corresponding to the intermediate temperature range (80 K–330 K) showed a variable activation energy between the grain boundaries. The barrier height, q¯, was estimated to 27±0.5 meV, and the standard deviation, qσ, was evaluated at about 14±0.5 meV. We found that at lower temperatures (20 K–80 K), the conductivity is governed by two conduction types. The density of localised states, was about 2.45×10²⁰ eV⁻¹ cm⁻³.