• Journal of the Korean Ceramic Society
• /
• v.36 no.7
• /
• pp.767-772
• /
• 1999

The effect of B2O3 addition on the sintering behavior dielectric and ferroelectric properties of Ba0.7Sr0.3TiO3 ceramics were investigated. The sample with 0.5wt% B2O3 was sintered under 115$0^{\circ}C$. The dielectric and ferroelectric properties of BST with 0.5wt% B2O3 was as good as BST without B2O3 sintered at 135$0^{\circ}C$ and its dielectric loss was even better When B2O3 was added over 1.0wt% the overdoped B2O3 remained in the specimens and formed a second phase which degraded the sintering behaivor dielectric properties of BST.

• Journal of the Korean Applied Science and Technology
• /
• v.32 no.1
• /
• pp.40-47
• /
• 2015

Single-walled carbon nanotubes (SWNTs) was modified with various length of linear alkyl chains and passivated to form dielectric filler. The modified SWNTs embedded into epoxy matrix to fabricate a flexible composite with high dielectric constant. The dielectric behavior of the composite was significantly changed with various alkyl chain length(n) of pyrene. The dielectric constant of the epoxy/SWNTs composite significantly increased with respect to increase in length of alkyl chain at the frequency range from 10 to 105Hz (n=12and18).We also found that the passivated epoxy/SWNTs composite with high dielectric constant presented low dielectric loss. The resulted dielectric performances corresponded to de-bundling of nanotubes and their distribution behavior in the matrix in terms of tail length of alkyl pyrene in the passivation layer.

• Journal of the Korean Ceramic Society
• /
• v.31 no.8
• /
• pp.841-848
• /
• 1994

The sintering behavior of La-modified PbTiO3 ceramics was investigated in order to improve the poor sinterability of PbTiO3. Addition of La improved the sinterability. It was confirmed that this improvement was due to the decrease in tetragonality ratio c/a of crystal lattice. The variations of dielectric constant and pyroelectric coefficient were measured with temperature. It was observed that with the increase of La content, Curie temperature decreased and dielectric constant at room temperature increased. La-modified PbTiO3 ceramics had smaller pyroelectric figure of merits than those of pyroelectric materials in use. The effects of grain size on dielectric and pyroelectric properties were also investigated. The change of grain size had effect on maximum dielectric constant and pyroelectric coefficient, but is had little effect on pyroelectric figure of merit at room temperature. The closer examination near ferro-paraelectric phase transition temperature revealed that the behavior of phase transition approached a more relaxor character with the increase of La content and the decrease of grain size.

• 한국정보디스플레이학회:학술대회논문집
• /
• 2003.07a
• /
• pp.1081-1084
• /
• 2003

Structural morphology, annealing behavior and dielectric properties of polyaniline-emeraldine base (Pani-EB) and poly methyl methacrylate (PMMA) thin films prepared by spin coating technique have been studied. MIM and MISM structures were used to investigate annealing and dielectric behavior. The XRD and AFM spectrum of as grown and annealed thin films indicates the amorphous nature. The observed amorphous phase, low loss, dielectric behavior and thermal stability even at high temperatures implies the feasibility of utilizing PMMA and Pani-EB thin films as gate dielectric insulator layer in organic thin film transistors which can find application in flat panel display.

• Smart Structures and Systems
• /
• v.12 no.5
• /
• pp.523-545
• /
• 2013

Piezoelectric and dielectric behaviors of a piezoceramic patch adhesively centered on a carbon composite plate are identified using a robust multi-objective optimization procedure. For this purpose, the patch piezoelectric stress coupling and blocked dielectric constants are automatically evaluated for a wide frequency range and for the different identifiable behaviors. Latters' symmetry conditions are coded in the design plans serving for response surface methodology-based sensitivity analysis and meta-modeling. The identified constants result from the measured and computed open-circuit frequencies deviations minimization by a genetic algorithm that uses meta-model estimated frequencies. Present investigations show that the bonded piezoceramic patch has effective three-dimensional (3D) orthotropic piezoelectric and dielectric behaviors. Besides, the sensitivity analysis indicates that four constants, from eight, dominate the 3D orthotropic behavior, and that the analyses can be reduced to the electromechanically coupled modes only; therefore, in this case, and if only the dominated parameters are optimized while the others keep their nominal values, the resulting piezoelectric and dielectric behaviors are found to be transverse-isotropic. These results can help designing piezoceramics smart composites for various applications like noise, vibration, shape, and health control.

• Macromolecular Research
• /
• v.17 no.10
• /
• pp.785-790
• /
• 2009

In this paper, the relaxation behavior of the regenerated silk fibroin (SF) films was investigated using dielectric thermal analysis (DETA), and compared with the dynamic mechanical behavior obtained from dynamic mechanical thermal analysis (DMTA), in order to gain a better understanding of the characteristics of dielectric behavior of SF film and identify the differences between the two analyses. Compared to DMTA, DETA exhibited a higher sensitivity on the molecular relaxation behaviors at low temperature ranges that showed a high $\gamma$-relaxation peak intensity without noise. However, it was not effective to examine the relaxation behaviors at high temperatures such as $\alpha-$ and ${\alpha}_c$-relaxations that showed a shoulder peak shape. On the contrary, DMTA provided more information regarding the relaxation behaviors at high temperatures, by exhibiting the changes in width, intensity and temperature shift of the $\alpha$-relaxation peak according to various crystallinities. Conclusively, DETA and DMTA can be utilized in a complementary manner to study the relaxation behavior of SF over a wide temperature range, due to the different sensitivity of each technique at different temperatures.

• Journal of the Korea Institute of Military Science and Technology
• /
• v.25 no.6
• /
• pp.580-585
• /
• 2022

In this study, the high-temperature dielectric constant of Si₃N₄ ceramics, a representative non-oxide-based radome material, was evaluated and the cause of the dielectric constant change was analyzed in relation to the oxidation behavior. The dielectric constant of Si₃N₄ ceramics was 7.79 at room temperature, and it linearly increased as the temperature increased, showing 8.42 at 1,000 ℃. As results of analyzing the microstructure and phase for the Si₃N₄ ceramics before and after heat-treatment, it was confirmed that oxidation did not occur at all or occurred only on the surface at a very insignificant level below 1,000 ℃. Based on this, it is concluded that the increase in the dielectric constant according to the temperature increase of Si₃N₄ ceramics is irrelevant to the oxidation behavior and is only due to the activation of charge polarization.

• Advances in materials Research
• /
• v.1 no.1
• /
• pp.93-107
• /
• 2012

Epoxy resin is widely used in high voltage apparatus as insulation. Fillers are often added to epoxy resin to enhance its mechanical, thermal and chemical properties. The addition of fillers can deteriorate electrical performance. With the new development in nanotechnology, it has been widely anticipated that the combination of nanoparticles with traditional resin systems may create nanocomposite materials with enhanced electrical, thermal and mechanical properties. In the present paper we have carried out a comparative study on dielectric properties, space charge and dielectric breakdown behavior of epoxy resin/nanocomposites with nano-fillers of $SiO_2$ and $Al_2O_3$. The epoxy resin (LY556), commonly used in power apparatus was used to investigate the dielectric behavior of epoxy resin/nanocomposites with different filler concentrations. The epoxy resin/nanocomposite thin film samples were prepared and tests were carried out to measure their dielectric permittivity and tan delta value in a frequency range of 1 Hz - 1 MHz. The space charge behaviors were also observed by using the pulse electroacoustic (PEA) technique. In addition, traditional epoxy resin/microcomposites were also prepared and tested and the test results were compared with those obtained from epoxy resin/nanocomposites.

• Journal of Surface Science and Engineering
• /
• v.56 no.3
• /
• pp.169-179
• /
• 2023

This work studies dielectric breakdown behavior of AAO (anodic aluminum oxide) films formed on pure aluminum at a constant current density in 5 ~ 20 vol.% sulfuric acid (SA) and 2 ~ 8 wt.% oxalic acid (OA) solutions. It was observed that dielectric breakdown voltage of AAO film with the same thickness increased with increasing concentration of both SA and OA solutions up to 15 vol.% and 6 wt.%, respectively, above which it decreased slightly. The dielectric breakdown resistance of the OA films appeared to be superior to that of SA films. After dielectric breakdown test, cracks and a hole were observed. The crack length increased with increasing SA film thickness but it did not increase with increasing OA film thickness. To explain the reason why shorter cracks formed on the OA films than the SA films after dielectric breakdown test, the generation of tensile stresses at the oxide/metal interface was discussed in relation to porosity of AAO films obtained from cross-sectional morphologies.

• Journal of Surface Science and Engineering
• /
• v.57 no.4
• /
• pp.254-264
• /
• 2024

This paper reviews the dielectric breakdown resistance and behavior of anodic oxide films in air environment. It begins with a description of the dielectric breakdown mechanisms of dielectric materials. The paper then introduces different types of dielectric materials and compares them in terms of dielectric strength, thermal conductivity, mechanical strength and cost. Next, the paper summarizes various fabrication methods for dielectric aluminum oxide layers, discussing the advantages and disadvantages of each method. Finally, it provides an overview of current studies on the dielectric breakdown properties of anodic aluminum oxide films formed on different aluminum alloys in various electrolytes.