Thermoelectric power of superionic conductor Ag7I4VO4

Thermoelectric power studies on Ag₇I₄VO₄. superionic conductor have been carried out in the temperature range 25 to 60°C. Thermo-electric power is found to vary linearly with the inverse of the absolute temperature, and can be expressed by the equation −θ = [(0.182 × 10³/T) + 0.276] mV/K. The heat of transport is nearly equal to the activation energy of Ag⁺ ion migration calculated from the conductivity plots indicating that the material has an average structure.     

Dielectric properties of nanophase Ag2HgI4 and Ag2HgI4-Al2O3 nanocomposites

The dielectric properties of nanophase Ag₂HgI₄ and Ag₂HgI₄-Al₂O₃ nanocomposites at different frequencies have been studied over a temperature range covering the stability range of β phase of Ag₂HgI₄ and beyond the β to a phase transition temperature. έ′, tan δ and σ_a.c. of nanophase Ag₂HgI₄ and Ag₂HgI₄-Al₂O₃ nanocomposites were found to be larger than the reported values for polycrystalline pellets of Ag₂HgI₄. The dielectric properties of the nanocomposites were found to be a function of the wt.% of nano alumina. The observed changes are attributed to the grain boundary properties of nanophase materials and to the microsize space charge effects.     

Preparation and photovoltaic properties of anodically grown Ag2O films

The semiconducting and photovoltaic properties of p-type Ag₂O films grown anodically on silver electrodes were studied, in view of possible applications in solar energy conversion. Films were grown in different alkaline solutions; the best results were obtained for 0.02M Ag₂SO₄ + 0.17M NH₄OH + 5.7 × 10^–3M Ba(OH)₂ saturated with Ag₂O powder, stirred mechanically at room temperature. Film thicknesses of up to 10m were thus obtained for the first time in anodically grown Ag₂O. Photovoltaic spectra taken at 300 K give a bandgap ofEg = 1.42 ± 0.04 eV. Evaporated gold on Ag₂O appears to be ohmic while aluminium and platinum are rectifying. The barrier height of Ag/Ag₂O is 0.90 ± 0.02 eV, that of Al/Ag₂O is 0.93 ± 0.02 eV, and that of platinum 0.94 ± 0.02 eV. The best cells give an open-circuit voltage,V _oc, of over 150 mV, and a short circuit current,I _sc = 100A cm^–2 under 50 mW cm^–2 illumination.     

La替代对Bi2O3-ZnO-Nb2O5陶瓷介电性能的影响

研究了A位La^3＋替代对Bi2O3-ZnO-Nb2O5（BZN）陶瓷结构和介电性能的影响。当La替代量X〈0．5时,陶瓷相结构为单一的立方焦绿石相。随着La替代量的增加,陶瓷样品的晶粒尺寸和密度逐渐减小。低温下的介电弛豫现象随着La替代量的增加也发生有规律的变化,介电常数逐渐减小,弛豫峰峰形逐渐宽化,峰值温度向低温方向移动。与La替代量为0．1、0．15、0．3和0．5相对应的弛豫峰的峰值温度分别为-95℃、-99℃、-109℃和-112℃。     

Dielectric and impedance properties of LiCa2Nb5O15 ceramics

Polycrystalline sample of LiCa₂Nb₅O₁₅ was prepared by a high-temperature solid-state reaction technique. Structural and microstructural characterizations were performed by X-ray diffraction (XRD) and scanning electron microscope (SEM). X-ray studies reveal that the material has orthorhombic structure at room temperature. Electrical properties of the material have been studied using a complex impedance spectroscopy (CIS) technique in a wide temperature (31–500 °C) and frequency (10²–10⁶ Hz) ranges. The complex impedance plots reveal the main contribution of bulk effects in it. The bulk resistance, evaluated from complex impedance spectrum, has been observed to decrease with rise in temperature showing a typical negative temperature coefficient of resistance (NTCR) behavior. Variation of dc conductivity (bulk) with temperature demonstrates that the compound exhibits Arrhenius type of electrical conductivity.     

纳米Al_2O_3/聚酰亚胺复合薄膜的介电与力学性能

采用原位聚合与热亚胺化的方法,成功制备了一系列不同纳米Al_2O_3粒子质量分数的纳米Al_2O_3/聚酰亚胺(PI)复合薄膜。通过SEM、TEM、XRD、FTIR、LCR数字电桥、高压电源及电子万能材料试验机对纳米Al_2O_3/PI复合薄膜的微观结构、介电性能及力学性能进行了表征和测试。结果表明:纳米Al_2O_3粒子在均匀地分散在PI基体中;当纳米Al_2O_3粒子质量分数为8%时,纳米Al_2O_3/PI复合薄膜的击穿强度和拉伸强度均达到了最大值;纳米Al_2O_3/PI复合薄膜的介电常数随纳米Al_2O_3质量分数的增加而增加。     

Dielectric properties investigation of Cu2O/ZnO heterojunction thin films by electrodeposition

Structures and morphologies of the Cu₂O/ZnO heterojunction electrodeposited on indium tin oxide (ITO) flexible substrate (polyethylene terephthalate-PET) were investigated by X-ray diffraction (XRD), scanning electronic microscopy (SEM), high resolution transmission electron microscopy (HRTEM), respectively. The dielectric response of bottom-up self-assembly Cu₂O/ZnO heterojunction was investigated. The low frequency dielectric dispersion (LFDD) was observed. The universal dielectric response (UDR) was used to investigate the frequency dependence of dielectric response for Cu₂O/ZnO heterojunction, which was attributed to the long range and the short range hopping charge carriers at the low frequency and the high frequency region, respectively.     

Preparation and properties of Tl2Ba2CaCu2O8 thin films

Anex situ process has been developed to produce thin superconducting Tl₂Ba₂CaCu₂O₈ films. The properties of films grown on different substrates using different annealing regimes were studied. Critical temperatures of 103–107 K were measured on films prepared in a broad range of annealing temperatures on SrTiO₃, LaAlO₃, and Y-ZrO₂ substrates. A critical current density,J _c, of 2×10⁶ A/cm² at 77 K was measured on LaAlO₃. Film morphology was studied by SEM, AFM, and STM.     

Enhanced dielectric properties of modified Ta2O5 thin films

 Tantalum oxide (Ta₂O₅) is a promising high dielectric constant material for the DRAM applications because of its ease of integration compared to other complex oxide dielectrics. The dielectric constant and thermal stability characteristics of bulk Ta₂O₅ samples were reported to enhance significantly through small substitutions of Al₂O₃. However, this improvement in the dielectric constant of (1-x)Ta₂O₅-xAl₂O₃ is not clearly understood. The present research attempts to explain the higher dielectric constant of (1-x)Ta₂O₅-xAl₂O₃ by fabricating thin films with enhanced dielectric properties. A higher dielectric constant of 42.8 was obtained for 0.9Ta₂O₅–0.1Al₂O₃ thin films compared to that reported for pure Ta₂O₅ (25–30). This increase was shown to be closely related to a-axis orientation. Pure Ta₂O₅ thin films with similar a-axis orientation also exhibited a high dielectric constant of 51.7, thus confirming the orientation effect. The leakage current properties and the reliability characteristics were also found to be improved with Al₂O₃ addition. Received: 24 November 1998 / Reviewed and accepted: 7 December 1998     

Electrical properties of Ta2O5 films deposited on ZnO

High dielectric constant (high-k) Ta₂O₅films have been deposited on ZnO/p-Si substrate by microwave plasma at 150°C. Structure and composition of the ZnO/p-Si films have been investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) for chemical composition. The electrical properties of the Ta₂O₅/ZnO/p-Si metal insulator semiconductor (MIS) structures were studied using high frequency capacitance-voltage (C-V), conductance-voltage (G-V) and current-voltage (I-V) characteristics. Charged trapping properties have been studied by measuring the gate voltage shift due to trapped charge generation under Fowler-Nordheim (F-N) constant current stressing.     

Synthesis and properties of thin SiO2-P2O5-CaO films

Thin SiO₂-P₂O₅-CaO films have been produced by a sol-gel process from film-forming solutions. The physicochemical processes underlying the formation of the films have been investigated, and their phase composition, structure, and bioactivity have been determined.     

Ta2O5薄膜的结构和电学性能研究

采用紫外光诱导热丝CVD沉积技术制备Ta2O5薄膜和Al/Ta2O2/SiMOS电容。利用XRD，AFM测试分析方法研究了紫外光源功率对Ta2O5薄膜结构的影响；通过C-V和，I-V测试对Ta2O5薄膜的介电常数，击穿场强和漏电流等电学性能进行了研究，结果表明：紫外光源的功率越大，Ta2O5薄膜的结晶性越好，介电常数越大，最大值为29，但紫外光功率对击穿场强和漏电流没有明显改善。     

Dielectric breakdown study of thin La2O3 films

The dielectric breakdown in La₂O₃ films of thickness 40–400 Å incorporated in capacitors is reported. The experimental results were analysed in the light of Forlani and Minnaja's theory of ionization avalanche breakdown. The dielectric breakdown strength was found to be a power function of thickness, varying as d^?0.66, in essential agreement with the theory of Forlani and Minnaja. Furthermore, these films are amorphous and have high breakdown fields (about 10 MV cm^?1).     

负热膨胀ZrW2O8薄膜的制备和性能

用交替射频磁控溅射法在石英基片上沉积并退火制备了ZrW2O8薄膜,测量了薄膜与基片之间的结合力和薄膜厚度,研究了薄膜的负热膨胀特性.结果表明:用磁控溅射方法制备的薄膜为非晶态,表面平滑、呈颗粒状,在1200℃热处理3 min后得到立方相ZrW2O8薄膜,结晶薄膜的颗粒长大,薄膜与基片之间有良好的结合力.立方相ZrW2O8薄膜在15-200℃热膨胀系数为-24.81×10-6K-1,200-700℃热膨胀系数为-4.78×10-6K-1,平均热膨胀系数为-10.08×10-6K-1.     

Dielectric and structural characteristics of Ta2O5 anodic films formed in phosphoric acid electrolytes

The duplex nature of Ta₂O₅ films formed in H₃PO₄ electrolytes with different concentrations has been chanyotarired by net weight gain measurements of the films during the anodic oxidation, as well by capacitance and etch-rate measurements of the oxide films. The density and permittivity of each layer of the films formed in different concentrations of the electrolyte have been calculated.     

Dielectric properties of BaBi2Nb2O9 ceramics

The crystal structure and dielectric properties as a function of temperature for Ba-based with Bi-layered structure BaBi₂Nb₂O₉ (BBN) ceramics were investigated. The obtained results confirmed the relaxor ferroelectric behavior of the studied ceramics, including a strong frequency dispersion of the permittivity maximum and a visible shift of its temperature with frequency. Analysis of the real and imaginary part of permittivity allowed us to determine the values of Burn’s temperature and of the freezing temperature characterizing the relaxor ferroelectrics. The physical processes, responsible for the relaxor behavior of the studied ceramics are discussed. The additional low frequency dielectric dispersion at high temperatures in the paraelectric phase range was also observed. Correlation between this dispersion and the thermally stimulated depolarization current was ascertained.     

Transport properties of textured Bi2Sr2CaCu2O8+y,thin films

Superconducting films of the high-T _c compound Bi₂Sr₂CaCu₂O_8+y , have been grown on (111)-oriented gadolinium gallium garnet substrates by a liquid-phase technique. The films show a very high degree of preferential orientation with thec-axis perpendicular to the substrates. The onset of the resistive transition was 85 K while zero resistance was obtained at 78 K. Results concerning the critical current properties of the films are described. Measurements of the paraconductivity effects on the electrical resistivity above the superconducting transition due to thermodynamic fluctuations are also reported.     

Dielectric properties of sol-gel derived Ta2O5 thin films

The dielectric constant and the dielectric loss of tantalum pentoxide (Ta₂O₅) thin films, produced by sol-gel spin-coated process on Corning glass substrates, have been investigated in the frequency range of 20-10⁵ Hz and the temperature range of 183-403 K, using ohmic Al electrodes. The frequency and temperature dependence of relaxation time has also been determined. The capacitance and loss factor were found to decrease with increasing frequency and increase with increasing temperature. The activation energy values were evaluated and a good agreement between the activation energy values obtained from capacitance and dielectric loss factor measurements were observed.