Shaoying Zheng

Dielectric and nonlinear current–voltage characteristics of rare–earth doped CaCu3Ti4O12 ceramics

CaCu3Ti4O12 (CCTO) ceramicsdoped with rare earth (RE) oxides, including Y2O3, La2O3, Eu2O3, and Gd2O3, were prepared by the traditional solid–state reaction method in order to investigate the effect of RE oxide dopants on the electrical properties as a varistor. The phase identification and morphology of the ceramics were investigated by x–ray diffraction(XRD) and scanning electron microscope (SEM), respectively. A high voltage measuring unit and precision impedance analyzer were used to determine the nonohmic (J–E) behaviors and measure the dielectric properties and impedance spectroscopy of the ceramics, respectively. The results showed that RE oxides enhanced greatly the breakdown electric flied but reduced the nonlinear coefficient and the mean grain size of CCTO ceramics. There was a good linear relationship between ln J and E 1/2, which demonstrated that the Schottky barrier should exist at the grain boundary. A double Schottky barrier model composed of a depletion layer and a negative charge sheet was proposed, analogous to the barrier model for ZnO varistors. The depletion layer width determined by diffusion distance of RE ions and the effective surface states played important roles on the electrical properties of the ceramics.

Electrostrictive and relaxor ferroelectric behavior in BiAlO3-modified BaTiO3 lead-free ceramics

The crystal structure of (1−x)BaTiO3-xBiAlO3 (x = 0, 0.02, 0.05, 0.08, and 0.1) ceramics was determined using X-ray diffraction and Raman spectroscopy at room temperature, which revealed a phase transition from tetragonal to rhombohedral with increasing x. The dielectric properties were studied as a function of temperature at different frequencies, which indicated that the phase transition temperature (Tm) decreased with increasing x. The relaxor behavior was observed by frequency and temperature dependent dielectric permittivity. The Lorenz-type quadratic law was used to characterize the dielectric permittivity peaks near Tm of high-temperature slopes at 1 MHz. The temperatures Tm of dielectric permittivity peaks fit very well with the Vogel-Fulcher law in x = 0.05 and x = 0.1. The polarization hysteresis loops and electrostrictive were displayed at room temperature. The sample for x = 0.1 exhibits a slim loop with negligible hysteresis and a subtle linear feature, which is a promising transducer materia...

Enhanced high-temperature piezoelectric properties of traditional Pb(Zr,Ti)O3 ceramics by a small amount substitution of KNbO3

Crystal structure, piezoelectric, and dielectric properties were investigated on the (1-x)Pb(Zr0.54Ti0.46)O3-xKNbO3 system. The piezoelectric properties have been significantly improved by substituting a small amount of KNbO3. In the morphotropic phase boundary (x = 0.015), the compound not only shows enhanced piezoelectric coefficient d33 = 450 pC/N, which is two times larger than that of unmodified Pb(Zr,Ti)O3 (d33 = 223 pC/N), but also the Curie temperature (TC = ~380 °C) is still well maintained at a high level. This phenomenon challenges our general knowledge that in piezoelectric materials the Curie temperature and piezoelectric properties are mutually contradictory. It should be noted that a giant total strain as high as 0.73% is also observed. The high thermal depoling temperature more than 300 °C combined with the excellent piezoelectric properties suggest it as a potential candidate for high temperature actuators and sensors applications.