The DC Bias Voltage Effect and Non-Linear Dielectric Properties of Titanate Nanotubes.

This work reports the nonlinear current-voltage behavior and the effects of dc bias voltage on the dielectric and electrical properties of titanate nanotubes (TNTs) prepared by hydrothermal method at 130 degrees C for 24 h. The TNTs sample exhibited high dielectric constant of > 10(4) at 100 Hz at room temperature with slight dependence on frequency in the range of 10(2)-10(4) Hz. The external resistance forms at the interface between electrode and surface sample. It was found that the dielectric constant of the sample decreased with increasing dc bias voltage due to the decrease in the electrode capacitance. For the study of the non-linear dielectric properties, the breakdown electric field (E(b)) value of the prepared TNTs sample obtained with J = 1 mA cm(-1) was found to be 149 V cm(-1). The E(b) value of the sample was significantly decreased with increasing temperature. The non-ohmic behavior tends to become linear ohmic in characteristic as the temperature increased.

Dramatically enhanced non-Ohmic properties and maximum stored energy density in ceramic-metal nanocomposites: CaCu3Ti4O12/Au nanoparticles.

Non-Ohmic and dielectric properties of a novel CaCu3Ti4O12/Au nanocomposite were investigated. Introduction of 2.5 vol.% Au nanoparticles in CaCu3Ti4O12 ceramics significantly reduced the loss tangent while its dielectric permittivity remained unchanged. The non-Ohmic properties of CaCu3Ti4O12/Au (2.5 vol.%) were dramatically improved. A nonlinear coefficient of ≈ 17.7 and breakdown electric field strength of 1.25 × 104 V/m were observed. The maximum stored energy density was found to be 25.8 kJ/m3, which is higher than that of pure CaCu3Ti4O12 by a factor of 8. Au addition at higher concentrations resulted in degradation of dielectric and non-Ohmic properties, which is described well by percolation theory.

CaCu3Ti4O12 nanoparticles using polyvinyl pyrrolidone: synthesis and dielectric properties.

Nanocrystalline CaCu3Ti4O12 powders with particle sizes of 39.28 8.12 nm were synthesized by a simple modify sol-gel using PVP (Poly-vinyl-pyrrolidone). The synthesized precursor was characterized by TG-DTA to determine the thermal decomposition and crystallization temperature which was found to be at above 500 degrees C. The precursor was calcined at 800 degrees C in air for 8 h to obtain nanocrystalline powders of CaCu3Ti4O12. The calcined CaCu3Ti4O12 powders were characterized by XRD, FTIR, SEM and TEM. Sintering of the powders was conducted in air at 1100 degrees C for 16 h. The XRD results indicated that all sintered samples have a typical perovskite CaCu3Ti4O12 structure and a small amount of CaTiO3. SEM micrographs showed the average grain sizes of 1.86 +/- 0.69 /m for the sintered CaCu3Ti4O12 ceramic prepared using the CaCu3Ti4O12 powders calcined at 800 degrees C. The sintered samples exhibit a giant dielectric constant, epsilon' of approximately 10(3)-10(4). The large low-frequency dielectric permittivity at low temperature is closely related to sub-grain boundary distribution, including conductivity effect. Furthermore, the ceramic shows three semicircles in the complex impedance plane. However, at low frequency, semicircles of sub-grain boundary and grain boundary are considered to represent collapse different electrical mechanisms. The another is ascribed to the contribution of grain. The dielectric behavior at several frequencies and temperatures of these samples can be attributed to electronic inhomogeneities present in material and can be explained based on a microstructural model.