掺杂水平对ZnO基变阻器电学性能的影响

根据相图规则设计、制备了三个系列不同Bi₂O₃与Sb₂O₃掺杂水平的ZnO基复合变阻器材料,研究了掺杂对氧化锌复合陶瓷电学性能的影响.研究发现,当Sb元素掺杂水平较低时,随着Sb₂O₃掺杂量的增加,所得氧化锌基变阻器材料漏电流的变化也很小,非线性系数(非线性系数α_L和击穿非线性系数α_B)将减小,而场强(场 关键词： 氧化锌 掺杂 复合陶瓷变阻器 电学性质     

The influence of Fe doping on the structural, magnetic and optical properties of nanocrystalline ZnO particles

We report the results of an investigation of Fe-doped nanocrystalline ZnO particles synthesized using the co-precipitation method with doping concentrations from 5 up to 31 at%. To understand how the dopant influenced the structural, magnetic and optical properties of nanocrystalline ZnO particles, X-ray diffraction, energy dispersive X-ray spectroscopy, infrared absorption spectroscopy, UV-vis spectroscopy, electron spin resonance spectroscopy (ESR) and vibrating sample magnetometer were employed. From the analysis of X-ray diffraction, our Fe-doped nanocrystalline ZnO particles are identified as having the wurtzite crystal structure and the unit cell volume increases with increasing doping concentrations. However, impurity phases are observed for Fe contents higher than 21 at%. Sample structures were further studied by infrared spectra, from which a broad and strong absorption band in the range of 400-700 cm⁻¹ and -OH stretching vibrational mode at approximately 3400 cm⁻¹ were observed. Ultraviolet-visible measurements showed a decrease in the energy gap with increasing Fe content, probably due to an increase in the lattice parameters. Magnetic measurements showed a ferromagnetic behavior for all samples. ESR results indicate the presence of Fe in both valence states Fe²⁺ and Fe³⁺.     

Effect of Y2O3 doping on the electrical transport properties of Sr2MnNiFe12O22 Y-type hexaferrite

Y₂O₃ doped Y-type composite hexa-ferrites Sr₂MnNiFe₁₂O₂₂ + xY₂O₃ (x = 0 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%) were synthesized successfully using sol-gel auto combustion technique. X-ray diffraction analysis reveals Y-type hexagonal structure with few traces of secondary phases. The decrease in grain size as a function of Yttrium content is attributed to the fact that Yttrium acts as a grain inhibitor. The DC resistivity was observed to increase with increasing Yttrium-contents due to the unavailability of Fe³⁺ ions at octahedral sites. Activation energy showed that the samples with high resistivity have high value of activation energy and vice versa. Permittivity decreases with the increase of frequency following Maxwell Wagner Model. In addition, the doped samples exhibit very low dielectric constant and low loss tangent in frequency range 20 Hz–1 MHz. The sample x = 5 wt% exhibit the lowest value of dielectric constant. The variation in imaginary part of dielectric constant and loss tangent with frequency show normal dielectric behavior for all the samples. The frequency dependent ac conductivity increases with increase in frequency and decrease with Y₂O₃ doping. These characteristics may be suitable for their potential applications in electromagnetic attenuation materials and microwave devices. The conductivity mechanism so determined was hopping mechanism. The dc resistivity of the doped ferrites measured in our case is about 10¹⁰ Ω-cm that meets the requirement for fabrication of components by electroplating.     

Effect of substitution of K ions on the structural and electrical properties of nanocrystalline MgAl2O4 spinel oxide

Potassium substituted nanosized magnesium aluminates having a nominal composition Mg_1−xK_xAl₂O₄ where x=0.0, 0.25, 0.5, 0.75, 1.0 have been synthesized by the chemical co-precipitation method. The samples have been characterized by means of X-ray diffraction (XRD), scanning electron microscope (SEM), and dc electrical resistivity measurements. The XRD results reveal that the samples are spinel single phase cubic close packed crystalline materials. The calculated crystallite size ranges between 6 and 8 nm. The behaviour of the lattice constant seems to deviate from the Vegard's law. While X-ray density clearly increases, the bulk density and consequently, the percentage porosity do not exhibit a significant change on increasing the K⁺ content. The SEM micrographs suggest homogeneous distribution of the nanocrystallites in the samples. The dc electrical resistivity exhibits a typical semiconducting behaviour. Substitution of a Mg²⁺ ion by a K⁺ ion provides an extra hole to the system, which forms small polaron. Thermally activated hopping of these small polarons is believed to be the conduction mechanism in the Mg_1−xK_xAl₂O₄. The activation energy of hopping of small polarons has been calculated and found K⁺ ions content dependent.     

Effect of Nd substitution on structural and electrical properties of nanocrystalline zinc ferrite

Polycrystalline soft ferrite samples with general formula ZnNd_xFe_2−xO₄ (where x=0, 0.01, 0.02 and 0.03) were synthesized by oxalate co-precipitation method. The samples were characterized by XRD and SEM techniques. The single phase cubic spinel structure of all the samples was confirmed by XRD. The lattice constant and grain size of the samples are found to decrease with increase in Nd³⁺ content. Room temperature DC resistivity of the Nd³⁺ substituted zinc ferrites is 10² times higher than that of zinc ferrite. The dielectric constant (ε′) and dielectric loss (tan δ) of all the samples were measured in the frequency range 20 Hz-1 MHz. The dielectric behaviour is attributed to the Maxwell-Wagner type interfacial polarization. The dielectric loss of the samples is found to decrease with increase in Nd³⁺ content. High resistivity and low dielectric loss makes these ferrites particularly suitable for high frequency applications.     

The temperature-dependent electrical transport properties of liquid Sn using pseudopotential theory

We present the calculations of electrical resistivity, thermo-electric power and thermal conductivity based on the self-consistent approximation. The pseudopotential due to Hasegawa et al. [J. Non-Cryst. Solids 117/118, 300 (1990) M. Hasegawa, K. Hoshino, M. Watabe, and H. Young, J. Non-Cryst. Solids 117/118, 300 (1990).[Crossref], [Web of Science ®] , [Google Scholar]] for full electron–ion interaction, which is valid for all electrons and contains the repulsive delta function to achieve the necessary s-pseudisation, was used in the calculation. Temperature dependence of structure factor is achieved through temperature-dependent potential parameter in the pair-potential. The outcome of the present study is discussed in the light of other such results and with predictions of Wiedemann and Franz law up to moderately high temperature. Specially, high-temperature resistivity data necessitates the careful investigation of electron energy dispersion close to the Fermi level and possible metal to non-metal transition while going from dense-fluid to low density-fluid state. In the absence of experimental data at high temperature, these findings may serve as future guideline.     

Structural and electrical properties of evaporated Fe thin films

Series of Fe thin films have been prepared by thermal evaporation onto glass and Si(1 0 0) substrates. The Rutherford backscattering (RBS), X-ray diffraction (XRD), Scanning electron microscopy (SEM) and the four point probe techniques have been used to investigate the structural and electrical properties of these Fe thin films as a function of the substrate, the Fe thickness t in the 76-431 nm range and the deposition rate. The Fe/Si samples have a 〈1 1 0〉 for all thicknesses, whereas the Fe/glass grows with a strong 〈1 0 0〉 texture; as t increases (>100 nm), the preferred orientation changes to 〈1 1 0〉. The compressive stress in Fe/Si remains constant over the whole thickness range and is greater than the one in Fe/glass which is relieved when t > 100 nm. The grain size D values are between 9.2 and 30 nm. The Fe/glass films are more electrically resistive than the Fe/Si(1 0 0) ones. Diffusion at the grain boundary seems to be the predominant factor in the electrical resistivity ρ values with the reflection coefficient R greater in Fe/glass than in Fe/Si. For the same thickness (100 nm), the decrease of the deposition rate from 4.3 to 0.3 Å/s did not affect the texture and the reflection coefficient R but led to an increase in D and a decrease in the strain and in ρ for both Fe/glass and Fe/Si systems. On the other hand, keeping the same deposition rate (0.3 Å/s) and increasing the thickness t from 76 to 100 nm induced different changes in the two systems.     

Nanostructural,magnetic and electrical properties of Ag doped Mn-ferrite nanoparticles

Nano-crystalline MnFe_2−xAg_xO₄ (x = 0, 0.1, 0.2, 0.3 and 0.6) samples with average grain size of 4–7 nm were synthesized by a simple method based on decomposition of metal nitrates in presence of citric acid. The samples were characterized by different structural, magnetic and electrical measurements. Rietveld refinement of X-ray diffraction data confirmed cubic spinel structure of the samples. Results show that Ag doping decreases the crystallite size, magnetization and coercivity of nanoparticles. By increasing the Ag content in the samples the saturation magnetization shows interesting temperature dependent behavior. It was realized that magnetization of smaller particles show higher sensitivity to temperature variations than larger particles. DC electrical resistivity measurements in the temperature range of 300–650 K show that the resistivity first increases and then decreases by increasing the Ag content in the samples. Curie temperature (T_c) and polaron activation energy in ferromagnetic and paramagnetic regions were estimated by using resistivity curves.     

Enhancement of electrical properties due to Cr substitution in Co-ferrite nanoparticles synthesized by two chemical techniques

Nanocrystalline cobalt ferrites with nominal composition CoCr_xFe_2−xO₄ ranging from x=0.0 to 0.5 with step increment of 0.25 were prepared by sol–gel auto combustion and chemical co-precipitation techniques. A comparative study of structural, electrical and magnetic properties of these ferrites has been measured using different characterization techniques. Structural and micro-structural studies were measured using X-ray diffraction, Fourier transform infra-red spectroscopy (FTIR), scanning electron microscopy and atomic force microscopy. Crystallite sizes of the series are within the range of 12–29±2 nm. Lattice parameters decrease by increasing Cr³⁺ concentration. FTIR confirms the presence of two lattice absorption bands. DC electrical resistivity increases to a value of ∼10¹⁰ Ω-cm with increase in Cr³⁺ concentration, but the most significant increase is in samples prepared by sol–gel combustion. Dielectric properties have been measured as a function of frequency at room temperature. Dielectric loss decreases to 0.1037 and 0.0108 at 5 MHz for chemical co-precipitation and sol–gel combustion, respectively. Impedance measurements further helped in analyzing the electrical properties and to separate the grain and grain boundary resistance effects using a complex impedance analysis. Magnetic parameters were studied using a vibrating sample magnetometer in the applied field of 10 kOe. The saturation magnetization decreased from 63 to 10.8 emu/gm with increase in Cr³⁺ concentration.     

Electrical,structural and thermal studies of carbon nanotubes from natural legume seeds: kala chana

ABSTRACT

Carbon nanotubes (CNTs) are the carbon materials measured at nanoscale level and they are defined in two types according to the number of concentric layers, i.e. single-layer tube is single-walled nanotubes, while multi-layer tube structure is called multi-walled nanotubes. The green method synthesis for the preparation of CNTs begins with the smashing of legume seeds kala chana, and then they form complex with cobalt salt. Desiccation of the complex compound forms cobalt salt and seed protein. The complex is then decomposed at 625 ºC in muffle furnace for 20 min. Purification of the decomposed sample is done through acid wash treatment and dried in vacuum oven. The confirmations of CNTs are done by nuclear magnetic resonance and Fourier transform infrared, which analyzes the denatured protein, reacted to the metal salt. X-Ray diffraction determines the MWNTs with transmission electron microscope (TEM) reports the network structure of CNTs. thermal gravimetric analysis (TGA)–differential thermal analysis (DTA)–thermogravimetric analysis (DTG) tests the amount of sample under thermal treatment. Vibrating sample magnetometer determines the paramagnetic nature of CNTs. CNTs thus prepared can be used in mechanical fields, in solar cells, in electronics fields, etc. because of their multidisciplinary properties. The synthesized CNTs are eco-friendly in nature, prepared by the legume seed natural precursor.     

Effect of Cu doping on the magnetic and electrical properties of n=2 Ruddlesden-Popper manganates

A series of polycrystalline Cu-doped n=2 Ruddlesden-Popper manganates La1.2Sr1.8CuzMn（2-x）O7 （x=0, 0.04, 0.13） were synthesized by the solid state reaction method. The effect of Cu doping on the magnetic and transport properties has been studied. It is found that Cu substitution for Mn greatly affects the magnetic and electrical properties of the parent phase La1.2Sr1.8Mn2O7. With the increase of Cu content, the system undergoes a transition from longrange ferromagnetic order to the spin glass state and further to an antiferromagnetic order. A little of Cu dopant can lead to the samples showing semiconductor or insulator behaviour in the whole observed temperature range while the parent phase has a metal-insulator transition. These samples show colossal magnetoresistance at low temperatures and the value of it decreases with increasing Cu content.     

液态铅的电阻率计算

根据费米面实验数据修正Behari关于液态铅的模型赝势,构建新的模型赝势,结合实验结构因子及硬球结构因子,计算不同温度下液态铅的电阻率,计算结果与实验数据较为符合,并对计算过程中的误差及模型赝势的适用性进行了分析. 关键词： 电阻率计算 电子输运 液态铅 模型赝势     

Influence of grain boundary state on electrical resistivity of ultrafine grained aluminium

An ultrafine grained (UFG) structure has been obtained in commercial purity Al by high-pressure torsion (HPT). Changes in microhardness and electrical resistivity of the UFG material after annealing at various temperatures within a range of 363–673 K have been investigated in correlation with the microstructure evolution. It has been shown that annealing at 363 K leads to substantial decrease in the electrical resistivity while keeping high microhardness level and approximately the same average grain size. The contributions from the various microstructural units (vacancies, dislocations, grain boundaries (GBs)) to the electrical resistivity were analysed. It was shown for the first time that a non-equilibrium state associated with strain-distorted grain boundary (GB) structure strongly affects electrical resistivity of UFG Al. The resistivity of non-equilibrium GBs in UFG structure formed by HPT was evaluated to be at least 50% higher than the resistivity of the thermally equilibrium GBs in a coarse-grained structure.     

Influence of iodine on the electrical properties of magnesium phthalocyanines thin film devices

The influence of iodine on the electrical properties of sandwich structures of magnesium phthalocyanine (Mg Pc) thin films with gold and aluminium electrodes has been investigated. The various electrical properties and different electrical parameters of the iodine-doped Mg Pc thin film devices have been estimated and compared with the values of normal Mg Pc devices from the analysis of the current-voltage characteristics. Generally samples showed an asymmetric conductivity both under forward and reverse bias. From our study we found that iodine doped Mg Pc films showed an enhanced electrical conductivity of nearly ten times that of typical Mg Pc. At low voltages the films showed an ohmic conduction with a hole concentration of P₀ = 6.34 × 10¹⁸ m⁻³ and hole mobility μ = 9.16 × 10⁻⁵ m ² V⁻¹ s⁻¹, whereas at higher voltage levels the conduction is dominated by space charged limited conduction (SCLC) with a discrete trapping level of 1.33 × 10²² m⁻³ at 0.63 eV above the valance band edge. The ratio of the free charges to trapped charges (trapping factor) for the doped samples was found to be 1.07 × 10⁻⁷. Furthermore the reverse conduction mechanisms have also been investigated. From the current limitations in the reverse condition a strong rectifying behaviour was evident which was attributed to Poole-Frankel emission with a field-lowering coefficient of value 2.24 × 10⁻⁵ eV m^1/2 V^−1/2.     

Improved electrical,magnetic and dielectric properties of polypyrol (PPy) substituted spinel ferrite composites

CoTb_0.03Fe_1.97O₄ ferrite and poypyrrole (PPy) polymer nano composites were prepared by mixing the nano crystalline ferrite with poypyrrole (PPy) by following the solid state reaction synthesis route. The XRD patterns of CoTb_0.03Fe_1.97O₄ spinel ferrite powders and polymer (PPy) exhibited single phase spinel structure. The amorphous nature of PPy was evidenced by the broad peaks of XRD patterns. The surface morphology unfolded heterogeneous distribution in composites and ferrite. The grains in ferrite were spherical in shape with clear boundaries. The morphology was appreciably altered by the inclusion of ferrite contents. The higher activation energy and resistivity aroused due to blocking of conduction mechanism owing to nanoparticles embedded in the PPy matrix. A downfall in the dielectric loss of the composites is observed as the frequency of the applied field is increased. The incorporation of ferrite contents optimized the magnetic parameters of the composites. The enhanced coercivity (Hc) of these nanocomposites might be beneficial for memory devices.     

运用第一性原理研究氧化锌电阻阀片中氧空位与掺杂条件下ZnO晶体电学性质

为了比较Nb_2O_5、MnO_2、MgO三种添加剂对氧化锌电阻阀片电学性能影响,在微观层面模拟Nb、Mn、Mg三种元素分别掺杂ZnO完整超晶胞和带有氧空位缺陷的ZnO超晶胞,并运用第一性原理分析掺杂晶胞的特性.本文计算了晶体结构、掺杂形成能、氧空位形成能、能带结构、态密度、载流子迁移率、电导率等.结果表明,掺入Nb原子的掺杂体系晶格体积最大,Mg掺杂体系的形成能最大,稳定性最弱,Nb掺杂氧空位形成能最低,更容易引入氧空位.Nb掺杂的ZnO超晶胞禁带宽度最小,氧空位缺陷增大掺杂晶体的禁带宽度.在相同掺杂浓度和同等条件下,Mn掺杂的晶体电导率最高.     

High pressure studies on the electrical resistivity of Ge–Te–Tl glasses

The variation of electrical resistivity in the system of glasses Ge₁₇Te_83?xTl_x, with (1≤x≤13), has been studied as a function of high pressure for pressures up to 10 GPa. It is found that the normalized electrical resistivity decreases continuously with the increase in pressure and shows a sudden drop at a particular pressure (transition pressure), indicating the presence of a transition from semiconductor to near-metallic at these pressures which are in the range 3.0–5.0 GPa. This transition pressure is seen to decrease with the increase in the percentage content of thallium due to increasing metallicity of the thallium. The transition is reversible under application of pressure and X-ray diffraction of samples recovered after pressurization show that they remain amorphous after undergoing a pressurization decompression cycle.     

紫外辐照对聚醚酰亚胺薄膜介电性能的影响

研究了不同紫外辐照时间对聚醚酰亚胺(PEI)薄膜介电性能的影响。采用FT-IR和SEM表征了PEI薄膜的分子结构和微观形貌。结果表明,紫外辐照后PEI薄膜在1742 cm-1处的吸收峰比原薄膜增大,说明PEI分子链中的C=O基团随辐照时间的增加而增加,并在薄膜表面产生了微裂纹。对PEI薄膜的介电性能进行的研究结果表明,随着紫外辐照时间的增加,PEI薄膜的介电常数和介电损耗增大,而表面电阻率下降,体积电阻率基本不变。并随紫外辐照时间的增加,直流击穿强度呈先增加后降低的趋势,一定辐照剂量可使薄膜发生交联反应,使击穿场强较原薄膜提高20%以上。     

Effect of compensation doping on the electrical and optical properties of mid-infrared type-II InAs/GaSb superlattice photodetectors

This paper presents a theoretical study on the electrical and optical properties of mid-infrared type-II InAs/GaSb superlattices with different beryllium concentrations in the InAs layer of the active region. Dark current, resistance-area product, absorption coefficient and quantum efficiency characteristics are thoroughly examined. The superlattice is residually n-type and it becomes slightly p-type by varying beryllium-doping concentrations, which improves its electrical performances. The optical performances remain almost unaffected with relatively low p-doping levels and begin to deteriorate with increasing p-doping density. To make a compromise between the electrical and optical performances, the photodetector with a doping concentration of 3 × 1015 cm-3 in the active region is believed to have the best overall performances.     

掺杂Fe对VH2解氢性能影响的第一性原理研究

采用密度泛函理论(DFT)的第一性原理的平面波超软赝势方法,研究了Fe掺杂对VH₂的电子结构和解氢性能的影响.通过计算Fe掺杂VH₂前后体系的合金形成热、V-H之间的重叠布居数、电子态密度、电子密度,发现Fe掺杂VH₂后,随着Fe含量增加,合金体系的晶胞参数和晶胞体积逐渐减少;体系的负合金形成热逐渐减少,且掺杂后体系的负合金形成热都比VH₂的负合金形成热小,体系的稳定性降低;电子态密度计算也显示Fe掺杂后费米能级处的电子浓度增加,体系稳定性降低;重叠布居数和电子密度计算表明掺杂后V-H之间的重叠布居数由0.1减小为0.08或0.09,V-H之间的电子密度减少,说明V和H原子之间的相互作用减弱,提高了VH₂的解氢性能.计算结果解释了实验现象. 关键词： Fe掺杂 电子结构 解氢性能 第一性原理计算