Chung-Sik Kim

Scaling behavior of ferroelectric hysteresis loop in pulsed-laser-deposited SrBi2Ta2O9 thin film

Ferroelectric SrBi2Ta2O9 thin films were grown on a highly oriented Pt/Ti/SiO2/Si substrates using pulsed laser ablation. The hysteresis loop of ferroelectric SrBi2Ta2O9 was studied as a function of applied field amplitude. A scaling analysis of ferroelectric hysteresis loop area showed A∝Eα. The value of scaling exponent, α=0.40, is not similar to the reported theoretical and experimental values. This result shows the possibility that both ferroelectric bulk and thin-film systems may have different universal behaviors. Influence of potential in the surface of SrBi2Ta2O9 thin film was measured in the dc applied field range from 0 to 8 V by using electro force microscopy. Roughness of surface potential of SrBi2Ta2O9 thin film changed rapidly around the coercive voltage, Vc∼1.5 V. It is believed that the switching effect of SrBi2Ta2O9 thin film includes surface polarization at the surface of the thin film as well as pure spontaneous polarization in the bulk.

Electrical properties of pulsed laser-deposited SrxBiyTa2O9 thin films on Bi/Sr ratios

Abstract The dependence of the electrical properties of Sr x Bi y Ta 2 O 9 thin films on the (Bi/Sr ratio 1.6, 2.3, 2.8, 3.4) has been investigated. The Sr x Bi y Ta 2 O 9 ferroelectric thin films were synthesized on Pt/Ti/SiO 2 /Si substrates using the pulsed laser deposition method. Saturation polarization ( P st ) and coercive field (2 E c ) depend on the Bi/Sr ratio. P st increases while E c decreases with an increase in Bi/Sr ratio. Atomic Force Microscopy images show that the grain size grows with increasing Bi/Sr ratio. It is observed that the impedance behavior in Sr x Bi y Ta 2 O 9 thin film, conforms to the Constant Phase Element (CPE) model. It is believed that the diffuse charges at the grain boundary build up a surface polarization because the impedance behavior close to pure capacitor with grain size increased.

ac conductance of surface layer in lithium tetraborate single crystals

ac conductance for the electrode effect in Li2B4O7 single crystal was investigated by use of a coplanar electrode applied on the surface of a (001) plate. A coplanar electrode in this material more clearly shows conduction of the electrode effect than a conventional parallel planar electrode. The electrode effect in ac conductance is likely to be controlled by the surface layer, which is a poorly conductive depletion layer possibly filled with vacancies of lithium ions. We found that the surface layer is not locally distributed near the electrodes, but, rather, on the broad area of the surface (001) plane of the material. So we conclude that the electrode effect in ac conduction of Li2B4O7 single crystal is mainly due to the poor conductive surface layer distributed over the whole surface of the (001) plane and is not a secondary phase formed by reaction with the electrode material.

Low Frequency Impedance Study of Li2B4O7 Single Crystals

For the study on the electrical characteristics in the electrode effect in lithium tetraborate (Li 2 B 4 O 7 ) single crystal, temperature dependence of dielectric constant and complex impedance in the low frequency (0.1 Hz–10 MHz) along the [001] axis was reported. Strong low frequency dispersion was observed in the complex dielectric constant scheme. Warburg type diffusion process was found in impedance study in the low frequency region, which maybe resulted from enhancement of chemical potential by activation of charge carriers in the deep potential well in the electrode region.