Bog-Gi Kim

FTIR study of fluorinated silicon oxide film

Fluorinated silicon oxide (SiOF) films were prepared by plasma enhanced chemical vapour deposition (PECVD) and studied by FTIR spectroscopic measurements. As fluorination dosage increased, the band intensity of the Si - F stretching mode was observed to increase but the peak frequency and band width remained unchanged. The Si - O vibrational bands were found to increase in frequency and decrease in band width. The Si - O asymmetric stretching band was analysed. It was found that the average bond angle of Si - O - Si bond increased but the distribution of the bond angles decreased in width as fluorination dosage was increased.

High Temperature Dielectric Anomaly of Ammonium Sulfate [(NH 4) 2SO 4] Crystal

Dielectric anomalies were observed in ammonium sulfate [(NH 4 ) 2 SO 4 ] crystals at T 0 ≃413 K after the crystal was heated above 413 K. Frequency dependence of dielectric loss across T 0 ≃413 K observed in the 2nd heating-up cycle could be best fitted by two overlapping relaxation functions of the Cole-Cole type. The fast component in higher frequency region depicts a sharp discontinuity of relaxation frequency at T 0 ≃413 K while the slow component in lower frequency region shows a continuous slowing down to zero relaxation frequency as temperature increased to T 0 ≃413 K.

Dimensionality crossover and the nonlinear dielectric response in betaine phosphate/arsenate mixed crystals

Dielectric properties of quasi-one-dimensional hydrogen-bonded chains are studied for mixed crystals of antiferroelectric betaine phosphate and ferroelectric betaine arsenate at three different mixing concentrations, x = 0.1, 0.3, and 0.4 (x being the concentration of arsenate). For mixed crystals with x = 0.3 and 0.4 dielectric study revealed dimensionality crossover at around 82 K, where the quasi-one-dimensional nature was turned into three-dimensional Curie - Weiss behaviour on lowering the temperature, well above the antiferroelectric transition point. For x = 0.1 mixed crystal, on the other hand, the crossover point was almost coincident with the antiferroelectric transition point, showing still too-weak interchain coupling and strong one-dimensionality, almost to the point of antiferroelectric transition. For this system, the electric bias field effect revealed temperature-dependent nonlinearity of the dielectric constant, which may be ascribed to a development of competition between antiferroelectric and ferroelectric interchain couplings, the latter growing with increasing bias field and lowering temperature.

Relaxation time distribution of deuterated dipole glass

Abstract We have shown that none of the well-known relaxation functions such as the Cole-Cole, Cole-Davidson and KWW functions are satisfactory to describe the observed dielectric relaxation behavior of the deuterated rubidium-ammonium dihydrogen phosphate dipole glass (DRADP-x). The correlated domain model of Chamberlin was in qualitative agreements with the experimental observations of the dipole glass for (i) a long tail at lower frequency side, (ii) increase in the asymmetry of the dielectric loss spectrum with decreasing temperature.

Anisotropic glass freezing in rubidium/ammonium dihydrogen phosphate mixed crystal and its deuterated analogue

Anisotropic glass freezing has been studied via dielectric measurements in the dipole glass systems of rubidium/ammonium dihydrogen phosphate RADP(x) and its perdeuterated analogue D-RADP(x), where x denotes the ammonium concentration. The glass freezing temperatures for a-cut and c-cut crystals are measured, and found to reveal very small anisotropy in the protonated sample of RADP(0.43) but a considerable anisotropy at low frequency in the deuterated sample of D-RADP(0.40). A higher glass freezing temperature was observed along the c-axis as compared with the a-axis freezing temperature for D-RADP(0.40) crystal. This conforms with the prediction of the cluster model theory for . An Arrhenius plot of the logarithmic relaxation frequency versus the reciprocal temperature for D-RADP(0.40) gave the deuteron activation energies along the a-axis and along the c-axis.

APPLICATION OF TIKHONOV REGULARIZATION TO DIPOLE GLASS RELAXATION FUNCTION

Abstract Relaxation distribution function g(τ) was derived from the experimental data of dielectric measurements by use of the Tikhonov regularization method of solving for the inverse solution of the integral transform defining the relaxation time distribution g(τ) in the dipole glass system undergoing the glass freezing. The distribution function g(τ) allows to calculate the average or effective relaxation time (τ). The temperature dependence of (τ) was studied in DRADP-x (x = 0.4) dipole glass and found to follow the Vogel-Fulcher law of glass freezing with the static freezing temperature T 0≃16.5K.

Relaxation distribution function in dipole glass in slow dynamics region

Relaxation time distribution function g(τ) was obtained by use of the Tikhonov regularization analysis from the low frequency dielectric data of a dipole glass (DRADP-x) at low temperatures. Temperature dependence of the average relaxation time, 〈τ〉=∫τg(τ,T)d(ln τ) was found to obey the empirical Vogel-Fulcher law. The dynamically correlated cluster model, however, could not reproduce our g(τ) and failed to give a satisfactory best fit to our dielectric data of a dipole glass.