Papers by Keyword: Dielectric Permittivity

Abstract: Electrodes play a vital role on the electrical properties of positive temperature coefficient (PTC) ceramics. An ohmic contract between ceramics and electrodes is necessary for the PTC effect. In this work, silver mixed aluminium electrode and pure silver electrode were pasted on BaTiO₃-based PTC ceramics, which results in an ohmic contact and non-ohmic contact, respectively. Impedance spectroscopy and dielectric and conductivity properties was investigated at different temperature for the two contacts. Small difference of electrical properties was found between the two contacts above the Curie temperature. Below the Curie temperature, however, carriers could pass through the interface of ohmic contract but gather on the interface of non-ohmic contact. The latter resulted in a space charge polarization, which increased low-frequency dielectric permittivity.

Abstract: The high dielectric permittivity of Y₂NiMnO₆ ceramics were measured by Agilent E4294A (Impedance Measurement) range of frequency 100 to 10 MHz in this research. In this sample ceramics, passing by a sintering temperature of 1400°C at 6 hours to 24 hours. The phase and microstructure of the deposited materials were investigated as a function of sintering temperature, using X-ray diffraction (XRD) and scanning electron microscopy (SEM). We found that the dielectric properties are very sensitive to the several sintered follow by time, and high temperature can be related to the change ordering of Ni²⁺ and Mn⁴⁺ ions.

Abstract: Dielectric properties of hydrothermally decomposed Y₂NiMnO₆ ceramics prepared under several sintering conditions were investigated at room temperature. As the results, dielectric constants at 200 Hz were found about 928 and 23x10³ for samples sintered at 1000 and 1400 oC, respectively. The dielectric permittivity for samples sintered at 1400 oC for different sintering times from 6 to 24 hours have yielded the best dielectric permittivity value of 10⁴. On the other hand, low sintering temperature had resulted in smaller dielectric loss in comparison to larger dielectric loss generally found in the ceramics with high sintering temperature.

Abstract: Based on effective medium theory, the temperature dependence of effective dielectric permittivity, ε_e(T), on core radius (a) and thickness (t) of non-ferroelectric dead layer (DL) on the surface of inhomogeneous grains of ferroelectric film made up of cylindrical ferroelectric grains was theoretically investigated. It was found that ε_e(T) increases with increasing core radius but decreases with increasing DL thickness. In this work, an equation expressing the relationship among ε_e, a and t was derived. This equation is very useful for the preparation of a ferroelectric film to desired properties.

Abstract: Polycrystalline of (1-x)ZnAl₂O₄ – xSiO₂ compound with compositions of x = 0.00, 0.05, 0.10, 0.15, 0.20 and 0.25 have been prepared using sol-gel method. Structural properties was investigated by atomic force microscopy (AFM) and x-ray diffractometer (XRD). The AFM images analysis showed that the surface roughness of the highest composition had rougher surface compared with other samples. XRD measurement indicated that the crystallite size also increased with average crystallite size around 18 nm with cubic phase had been found. The dielectric permittivity value were measured with frequency range of 1 Hz to 1 MHz. It is showed that the dielectric value decreased as the freqeuncy was applied to the samples. The performance of the patch antenna showed that the antenna resonated at 3.30 GHz and give-13.87 dB with frequency range about 2 – 4 GHz.

Abstract: PbFeBO₄ and PbMnBO₄ single crystals were synthesized. The X-ray, magnetic, dielectric, Mössbauer, and resonance investigations of the crystals were fulfilled. It is established that single-crystal PbFeBO₄ is an antiferromagnet with a Néel temperature T_N =114 K, while PbMnBO₄ is a ferromagnet with a Curie temperature T_C = 31 K. Both single-crystal compounds have a strong anisotropy of the magnetic and dielectric properties.

Abstract: The relation between the dielectric tunability and the electro-optic (EO) effect of barium strontium titanate (Ba_0.5Sr_0.5TiO₃) thin film was discussed. The tunability of dielectric permittivity calculated from the complex admittance with planer electrodes reached to 53.1%, and the tunability of birefringence by EO effect was 0.6%. The birefringence change from EO effect was much lower than the tunability of dielectric permittivity. The materials with high tunability do not always exhibit high EO effect. This is concluded to arise due to the ionic mass in the EO materials.

Abstract: The paper presents a comparative study of Ca_0.25Cu_0.75TiO₃ (CCTO) electrical properties produced by two methods - mechanochemical synthesis and high temperature treatment. Products differ significantly in terms of grain morphology and the degree of defects in structure. This is the reason why electrical properties are different.

Abstract: A new kind of two phase ammonium dihydrogen phosphate (NH₄H₂PO₄ or ADP)/polyvinyl alcohol (PVA) composite films have been prepared by solution cast technique. Significant enhancement of dielectric permittivity (~442) of ADP/PVA composites are observed at low ADP concentration (f_ADP f_C ~5 wt %) which is the percolation threshold value estimated from the concentration dependent transport and dielectric data. Nearly 85 times increase in dielectric permittivity compared to that of the bare PVA film in the composite film around f_C with low loss (~0.14) at 1 kHz and room temperature is observed. The present ADP based PVA composite material might be processed for application in devices.

Abstract: The polymer blend of Ethyl Cellulose (EC) with Poly (vinyl) pyrrolidone (PVP) of various weight percentages at different thickness are used for measurement of dielectric permittivity, electrical conductivity and optical properties. The activation energies of the EC and its blend with PVP are obtained through measurement of dc conductivity. The samples are characterized by using X-ray diffractometer (XRD). The blends of EC with PVP in the ratio of 50:50 weight percent using FTIR over the range of wavenumber 4000-500 cm^-1. Key words: Polymer Blend, XRD, SEM, FTIR, dielectric permittivity, activation energy.