Papers by Keyword: Dielectric Relaxation

Abstract: Features of processes of a dielectric relaxation and charge transport in photorefractive sillenite crystals Bi₁₂TiO₂₀ at low frequency range are investigated. It was found that the dispersion of dielectric permittivity ε' in crystals Bi₁₂TiO₂₀ is characterized by its growth with lowering frequency and rising temperature. This behaviour may be related to existence of dipole-relaxation polarization mechanism. The frequency dependence of dielectric loss tgδ reveals the existence of low frequency relaxation peaks in the studied temperature range. From the conductivity dependence on the frequency and temperature it was found that conductivity σ increases as frequency increases in the low frequency range. The observed dependence σ(ω)≈Аω^s indicates that transport mechanism is due to hopping of carriers via localized electron states. The charge transport is thermally activated process in which activation energy E_a = (0.82±0.03) eV.

Abstract: Single-phase of BaCe_0.57Zr_0.38Yb_0.05O_2.975 (BCZYb) has been successfully prepared by a Pechini method using metal nitrate salts as pre-cursor. Dielectric behavior of the BCZYb sample was studied using impedance data collected from High Frequency Response Analyzer (HFRA). The frequency and temperature dependence of the dielectric constant and dielectric loss of the BCZYb solid solutions were investigated in the 1 Hz - 1 MHz frequency range. Dielectric relaxation mechanism was observed in the plots of dielectric constant and loss versus temperature. It was studied by the measurements of intermediate temperature, 500 - 800 ° C. All the responses were revealed by the analysis of impedance spectroscopy, using Z-man program. The present results are used to observe the relation between orientation polarization and dielectric relaxation of the material.

Abstract: Dielectric relaxation and conductivity of Ni_0.3Zn_0.7Fe₂O₄ (NZF) were studied in the frequency range between 0.01 Hz to 3 MHz and temperature range within 313 K to 473 K. The sample was prepared by mixing Zinc Oxide, Nickel Oxide and Iron Oxide and sintered at 1573 K for 10 hours long. Dielectric properties were studied using Novo Control Dielectric Spectrometer. Dielectric relaxation and conductivity phenomena were discussed using an empirical model to key out the dielectric relaxation process. Analyze peak frequency relaxation process consist of four slopes to explain the dielectric relaxation process. The conductivity of the sample indicates an activated process and activation energy of dc conductivity is 0.44 ± 0.01 eV.

Abstract: The influence of barium doping on the oxygen-ion diffusion and phase transition in the La₂Mo_2-yW_yO_9-δ (y=0, 1.0) oxide-ion conductors has been systematically investigated via dielectric techniques. In the Ba-doped La₂Mo₂O₉ samples there are only two dielectric relaxation peaks P_d1 and P_d2, which are associated with the short-distance diffusion of oxygen vacancies. But in the Ba-doped La₂MoWO₉ members, three peaks are detected, including peak P_d1, P_d2, and peak P_h. The last is associated with the phase transition process from the static disordered state to the dynamic disordered state of oxygen ion/vacancy distribution.

Abstract: Lanthanide doped/based oxide thin films were deposited by liquid injection metal organic chemical vapor deposition or atomic layer deposition. Frequency dispersion is often found in the capacitance-voltage measurements. After taking the extrinsic frequency dispersion into account, the frequency dependence of the dielectric constant (k-value), that is the intrinsic frequency dispersion (dielectric relaxation) has been successfully theoretically modeled. For the physical mechanism of the dielectric relaxation, it was found that the effect of grain sizes for the high-k materials structure mainly originates from higher surface stress in smaller grain due to its higher concentration of grain boundary. Variations in the grain sizes of the samples are governed by the deposition and annealing conditions and have been estimated using a range of techniques including Scherrer analysis of the X-ray diffraction patterns. The relationship extracted between grain size and dielectric relaxation suggests that tuning properties for improved frequency dispersion can be achieved by controlling grain size, hence, the strain at the nanoscale dimensions.

Abstract: Ferroelectric ceramics, Sr_1-xLa_xBi₂Nb_2-x/5O₉ (SLBNO), were prepared using the conventional solid-state reaction method. Effect of lanthanum substitution on dielectric and ferroelectric properties of SrBi₂Nb₂O₉ (SBN) ceramics were investigated. X-ray diffraction analyses (XRD) revealed that all the specimens had a single phase with orthorhombic space group A2₁am. The maximum dielectric permittivity peak broadened gradually with the increase in lanthanum substitution indicated that the phase transition from normal ferroelectrics to relaxor ferroelectrics occurred in SLBNO ceramics. The modified Curie-Weiss (CW) law was used to describe the relaxor behavior of the SLBNO ceramics. The relaxation indication coefficient (γ) was estimated from a quadratic fit of modified CW law and was found to be 1.7 and 2.0 for the SLBN20 and SLBN30 specimens, respectively. Curie temperature (T_c) of the SBN ceramic was decreased gradually with the increase in lanthanum substitution. In addition, the ferroelectric properties of the SBN ceramic were enhanced significantly by the introduction of lanthanum ions and the maximum of remnant polarization (P_r) was found to be 4.35 μC/cm² for the SLCB20 specimen. Nature of relaxor behavior of the SLBNO ceramic is attributed to the cationic disordering at nanoscale on A site by the introduction of lanthanum ions.

Abstract: The effects of tungsten doping in La2Mo1.5W0.5O9 sample were studied using dielectric relaxation measurements. The results indicate that W6+ can suppress the α/β phase transition in the La2Mo2O9. Additional to the low-temperature relaxation peak Pd associated with oxygen ion diffusion, a new dielectric loss peak Ph associated with a phase transition from the static disordered state to the dynamic disordered state of oxygen ion distribution was observed around 740 K.

Abstract: Nano-sized powders of dielectric CaCu₃Ti₄O₁₂ was synthesized by sol-gel reaction route. The powders are calcined at 700 °C and sintered at 1000 °C. The calcined powders diameter is in the range of 50 - 150 nm. Structural studies were carried out using the XRD, HRTEM and SEM. Frequency dependent dielectric properties were studied within the range of 20 Hz to 5 MHz. Molecular kinetics associated with dielectric relaxations is analyzed by Havriliak Negami function. It is found that the grain dipoles obey the Debye type of dielectric relaxation, while grain boundary dipoles follow the Cole-Cole type of dielectric relaxation. The observed grain and grain boundary dipole relaxation time are 6.598E-08 sec and 5.755E-04 sec, respectively.

Abstract: . In this paper, dielectric relaxation and reliability of high capacitance density metal-insulator-metal (MIM) capacitor using Al2O3-HfO2-Al2O3 sandwiched structure were analyzed. It is shown that multilayer MIM capacitor provides high capacitance density and low dissipation factor at room temperature. The dielectric relaxation voltage shows little dependence on the capacitor area. The capacitance density (C0) increases and quadratic voltage coefficient (α) decreases as a function of stress time under constant voltage stress (CVS) because of the charge trapping effect in the high-k dielectric.

Abstract: The influence of humidity content on the electrical and dielectric properties of a composite made from recycled TetraPak® containers and granulated cork was studied. The material components have been dried before preparation and after the composite was conditioned by keeping the samples in a dry environment (desiccator) or in an oven at high temperature (70°C in air). The differences observed in electrical properties (investigated by isothermal charge and discharge current measurement) and dielectric properties (measured using dielectric relaxation spectroscopy) show that the thermal treatment at high temperature is more efficient on removing water and slows down the re-absorption rate.