Zang Guo-Zhong

Nonlinear Electrical Behaviour of Composite SnO2–Zn2SnO4 System

We have found a new composite SnO2?Zn2SnO4 varistor material and the effect of different content ratios of SnO2 to Zn2SnO4 on this system is investigated. The lowest breakdown voltage (EB = 6.4?V/mm) and the highest relative dielectric constant (?r = 1.54?104) with higher nonlinear coefficient (? = 4.5) is obtained when the ratio of SnO2 to ZnO equals 100/35. The disappear of the Zn2SnO4 peak in x-ray diffraction (XRD) spectra of the SnO2+2.5?mol%ZnO sample and the electric insulation behaviour of the samples with 2.5?mol% ZnO and 200?mol% ZnO indicate that 2.5?mol% ZnO can be dissolved into SnO2 lattices and some reaction contributing to nonlinear electrical behaviour should occur between SnO2 and Zn2SnO4. The role of oxygen on the grain boundary is confirmed by the degradation of nonlinear electrical properties and the increase of relative dielectric constant of the samples annealed in nitrogen-rich atmosphere.

(Na0.52K0.44Li0.04)Nb0.9-xSbxTa0.1O3 Lead-Free Piezoelectric Ceramics with High Performance and High Curie Temperature

(Na0.52K0.44Li0.04)Nb0.9-xSbxTa0.1O3 lead-free piezoelectric ceramics are prepared by a solid-state reaction method. With increasing Sb content, the transition temperature from orthorhombic to tetragonal polymorphic phase decreased. A composition (Na0.52K0.44Li0.04)Nb0.863Sb0.037Ta0.1O3 is found to possess excellent piezo-electric and electromechanical performances (d33 = 306 pC/N, kp = 48%, and kt = 50%), and high Curie temperature (TC = 320°C). These results indicate that (Na0.52K0.44Li0.04)Nb0.863Sb0.037Ta0.1O3 is a promising lead-free piezoceramics replacement for lead zirconate titanate.

Phase Structures of (K0.48Na0.52)0.945 Li0.055Sb0.05Nb0.95O3 Piezoceramics

The phase structures of lead-free (K0.48Na0.52)0.945 Li0.055Sb0.05Nb0.95O3 piezoceramics are studied based on the measurements of ferroelectric and dielectric properties as well as the analyses of x-ray diffraction pattern and energy dispersive spectroscopy. The poled samples exhibit orthorhombic structure whereas the surface and interior for unpoled samples exhibit tetragonal and tetragonal-orthorhombic coexistent structures, respectively. These results are in agreement with the relative permittivity-temperature curves and demonstrate that phase transitions can be induced by Na volatilization and poling process. The remnant polarization Pr measured at 20°C increases continuously with the increase of electric held in the range of 2000–4000 V/mm. This indicates that the polymorphic structure is more beneficial to the rotation or reorientation of dipoles than either the orthorhombic or the tetragonal structure. The randomly oriented domains may be the essential reason for the continuous rotation or reorientation and not good thermal stability.