Invited paper: Dielectric properties of CaCu3Ti4O12 polycrystalline ceramics

Abstract

We investigated the relationship between the microstructures and dielectric properties of various CaCu3Ti4O12 (CCTO) polycrystalline ceramics sintered in air. An abrupt increase in the dielectric constant (εr) from ~3,000 to ~170,000 at 1 kHz occurred with increasing the sintering temperature from 980 to 1000°C for 12 h, respectively, which was accompanied by a very large increase in the average grain size from 5 to 300 µm, respectively, due to an abnormal grain growth. With further increasing the sintering temperature, the εr value at 1 kHz was slightly decreased to ~150,000 at 1020°C with no variation in the average grain size, significantly decreased to ~77,000 at 1040°C with a large decrease in the average grain size (~150 µm), and then maintained the values of ~76,000 and ~69,000 at 1060 and 1080°C, respectively, without noticeable variation in the average grain size. While no abnormal grain growth occurred in the CCTO samples sintered at 980ºC for the holding time to 24 h and thus their εr values showed relatively lower εr values (< ~4,000 at 1 kHz), the abnormal grain growth occurred in the samples after a certain holding time at a given sintering temperature of higher than 1000°C and thus their εr values abruptly increased. Analyses by the complex impedance (Z*) and modulus (M*) spectroscopy revealed that the εr values of the CCTO samples were dominantly affected by the electrical properties of grain boundary so that high εr values over 10,000 at 1 kHz were attributable to the high capacitance (C) of grain boundary, which is in good agreement with grain boundary internal barrier layer capacitor (IBLC) model.

A Novel One‐Step Flame Synthesis Method for Tungsten‐Doped CCTO

“…The E a values are calculated from the slope of ln τ versus 1/ T plots of the impedance, and modulus data are listed in Table . These activation energies of the CCTWO ceramics are in close agreement with the values calculated for the grain‐boundary contribution previously reported …”

“…All the spectra are characterized by the appearance of a peak, shift in the peak position toward higher frequency, and typical peak broadening with increasing temperature, which behavior indicates the presence of a temperature‐dependent electrical relaxation phenomenon in the ceramics. Similar type behavior has been reported for CCTO and other perovskites …”

Simultaneously enhanced device efficiency, stabilized chromaticity of organic light emitting diodes with lambertian emission characteristic by random convex lenses

“…The difference in the refractive indices (ns) defines the angle of the escape cone. If the light travels from a layer with a high n toward a low n, significant portion of the light will be confined due to the total internal reflection (TIR) [32]. The out-coupling limit imposed by the TIR is detrimental to the efficiency and lifetime of the device.…”

Light out-coupling enhancement of organic light emitting devices using nano-structured substrate produced by rapid thermal processing

“…Organic light-emitting devices (OLEDs) have attracted many researchers during the last two decades for their potential applications in large-area solid-state lighting and next generation self-luminous display devices [1]. The researchers' great interest in these devices is due to their simple fabrication techniques, such as thermal evaporation, solution-based spincoating, ink-jet printing and roll-to-roll processing.…”

“…However, one of the major problems of these devices is that about 30% light is lost at the substrate-air boundary due to TIR and about 50% light is lost due to the wave-guiding effect at the ITO-organic and ITO-substrate boundaries. Due to the combined effect of TIR at the glass-air boundary and wave-guiding at the ITO-glass/ITO-organic layers a total 80% light is lost [1][2][3]. This is due to the large refractive index contrast between the ITO-organic layers, ITO-glass and glass-air boundaries.…”