Interfacial characteristics of Al/Al2O3/ZnO/n-GaAs MOS capacitor

The interfacial characteristics of Al/Al2O3/ZnO/n-GaAs metal-oxide-semiconductor (MOS) capacitor are investigated. The results measured by X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM) show that the presence of ZnO can effectively suppress the formations of oxides at the interface between the GaAs and gate dielectric and gain smooth interface. The ZnO-passivated GaAs MOS capacitor exhibits a very small hysteresis and frequency dispersion. Using the Terman method, the interface trap density is extracted from C-V curves. It is found that the ZnO layer can effectively improve the interface quality.     

Dielectric spectroscopy studies of ZnO single crystal

Dielectric relaxation and charge transport induced by electron hopping in ZnO single crystal are measured by using a novocontrol broadband dielectric spectrometer. Typical Debye-like dielectric relaxation originating from electronic hopping between electronic traps and conductive band in surface Schottky barrier region is observed for ZnO single crystal-Au electrode system. However, after insulation of ZnO single crystal by heat treatment in rich oxygen atmosphere, dielectric relaxation and alternating current conductance are observed simultaneously in the dielectric spectra, implying that dielectric relaxation and charge transport can be induced simultaneously by electronic hopping at high temperature in an ordered system. The intrinsic correlation between local dielectric relaxation and long range charge transport offers us a new method to explore complicated dielectrics.     

Dielectric and structural relaxation phenomena in Na0.5Bi0.5TiO3 single crystal

Abstract

Dielectric permittivity studies of Na_0.5Bi_0.5TiO₃ single crystals in a broad range of frequency up to 10 MHz and temperature 300—823 K are reported. In this temperature range dielectric dispersion below 1 MHz has been found. The obtained data were fitted to the Cole-Cole relation. The mean relaxation time τ is strongly temperature dependent (0.04 ? 2.6 × 10^?5 s). A remarkable hysteresis effect in the values of τ on cooling and heating took place. The Δε(T) dependence (the maximal value of Δε ～ 400) is similar to the global ε′(T) response at low frequency. An isothermal structural transformation in Na_0.5Bi_0.5TiO₃ was observed by X-ray measurements. The order of the time in which the transformation takes place (～300 minutes) corresponds to the time in which the strongest time evolution of electric permittivity and time changes of dielectric dispersion were detected.     

Bounds on the reflectivity of two-component composite

Bounds on the effective permittivity circumscribe 2D area in the complex plane representing possible values of permittivity. It is shown that the corresponding possible values of reflectivity occur within the interval determined by the lowest and the highest reflectivity value, which represent minimum and maximum values of reflectivity found at the permittivity bounds.     

Crystal chemical and dielectric study of niobochromates with the tungsten bronze structure

Abstract

A crystal chemical study has allowed us to identify new niobochromates crystallizing with the tungsten bronze structure: Ba₂LnNb₄CrO₁₅ (Ln = Bi, La), La₂ANb₄CrO₁₅ (A = Li, Na, K) and Ba₂Na_1-x La _x Nb_5-x Cr _x O₁₅ (0 ? x ? 1). A dielectric study has shown that the T _c (x) curve goes through a minimum at x ? 0.5 along the solid solution Ba₂Na_1-x La _x Nb_5-x Cr _x O₁₅, while the ferroelastic transition T_c changes very slightly in the same range of composition.     

Elastic,impedance spectroscopic and dielectric properties of TiO2 doped nanocrystalline NiCuZn spinel ferrites

ABSTRACT

Nanocrystalline Ni_0.4Cu_0.3Zn_0.3Fe₂O₄ ferrites doped with TiO₂ (0–10?wt %) were prepared by the sol-gel method. Elastic properties of synthesized samples were studied with the help of ultrasonic pulse transmission method. The elastic constants initially increase with an increase in TiO₂ up to 1?wt % and then decline. LCR-Q meter was used to study the dielectric properties within 50?Hz to 5?MHz range of the frequency. The dielectric constant (?′) and dielectric loss tangents were decreased continuously with increased frequency for all the selected samples at room temperature revealing normal dielectric behavior of ferrites. Also, the AC conductivity was increased with an increase in the frequency for all the selected samples. Cole-Cole plots were obtained for all investigated samples and showed single semicircle which indicates that the electrical conduction process appears only due to grain boundaries.     

Influence of silica nanoparticles on dielectric spectroscopy and polarization switching responses of novel ferroelectric liquid crystals

Silica (SiO₂) nanoparticles in different wt/wt% ratios were dispersed in a novel room temperature ferroelectric liquid crystal mixture. Dielectric relaxation spectroscopy (50 Hz–1 MHz) and electro-optic responses were investigated. Dielectric permittivity gradually decreases by about 40% up to 1 kHz with increasing SiO₂ concentration in the chiral smectic C phase. However, an increase of up to 1.5% has been observed for all the silica-doped samples above 2 kHz. We noticed an increase in optical transmission with increasing SiO₂ concentration from 0.01 to 0.1 wt/wt%.     

Time evolution of polar regions in (Sr0.65Ba0.35)2NaNb5 O 15 single crystal

The linear, second-order and third-order dielectric susceptibilities χ₁, χ₂, χ₃ of a (Sr_0.65Ba_0.35)₂NaNb₅O₁₅ (SBNN) single crystal have been measured. Strong relaxation was found in all investigated dielectric susceptibilities near the phase transition. The time dependence of linear and third-order dielectric susceptibility can be explained as the effect of polar nano-clusters evolution. Near the phase transition, the net polarization of the crystal, monitored by second-order dielectric susceptibility, changes both its value and orientation. Measurements of the pyroelectric effect indicate that the non-zero net polarization in SBNN crystals appears spontaneously. In addition, the ferroelectric phase transition in SBNN showed many features of a first-order phase transition.     

Effect of the chiral chain length on structural and phase properties of ferroelectric liquid crystals

Studies of structural and phase properties obtained on several ferroelectric liquid crystalline materials with 2-alkoxypropionate group used as a chiral centre and without any lateral substitution are presented. In dependence on the chiral chain length these compounds exhibit the cholesteric N* phase, the ferroelectric smectic C* and a low-temperature SmX phase. Values of the spontaneous polarization and spontaneous tilt angle have been determined within the whole range of the SmC* phase. A low-temperature SmX phase has been identified as the orthogonal hexatic SmB* phase. The molecular parameters, namely the layer spacing in the SmC* and SmB* phases and the average intermolecular distances (D) between neighbouring parallel molecules in all investigated phases have been determined using the results of the X-ray diffraction obtained on non-oriented samples. The effect of the chiral chain length on mesomorphic, structural and physical properties of the studied ferroelectric liquid crystalline materials is discussed.     

Dielectric Measurements as a Function of Temperature of Sodium‐Lithium Phosphate Glasses Evaluated at 10 MHz and 9 GHz

Dielectric constant measurements can be performed at temperatures greater than room temperature; some techniques are shown in this work. The dielectric constant of phosphate glasses, measured in the X‐band microwave range, was determined using a microwave setup assembled to measure the shift in the standing wave pattern produced by the insertion of the sample inside the waveguide. The glass system 50P₂O₅ · 25Li₂O · 25Na₂O was chosen in this work due to its lower melting point and lower transition temperature (T_g) values. The dielectric constant of the glass studied in this work increases in the temperature range 25–330°C, as shown by the results at radio and microwave frequencies. The method of standing wave shift was applied, and it is shown to be a useful tool to estimate the T_g of glasses. This assumption was confirmed by differential thermal analysis technique. Measurements were compared to that at 10 MHz by impedancimetric methods.