Mingsong Wang

Double hysteresis loop induced by defect dipoles in ferroelectric Pb(Zr0.8Ti0.2)O3 thin films

Pb(Zr0.8Ti0.2)O3 (PZT80/20) thin films were deposited on the Pt(111)/Ti/SiO2/Si(100) substrates by RF magnetron sputtering. Mainly perovskite crystalline phase with highly (202)-preferred orientation, determined by x-ray diffraction, was formed in the lead zirconate titanate (PZT)(80/20) thin films. Polarization measurements of the unannealed and aged films showed a clear double hysteresis loop. However, the double hysteresis loop phenomenon was greatly suppressed in the PZT thin films annealed under pure oxygen, and thus they exhibited larger remnant polarization (Pr = 6.3 μC/cm2). The related mechanism for the appearance of constricted and double hysteresis loops was investigated to be associated with the realignment and disassociation of defect dipoles via oxygen octahedral rotations or oxygen vacancy diffusion. The butterfly-shaped C-V characteristic curve with a valley gave further evidence for double hysteresis loop characteristic in the unannealed and aged PZT thin films.

The Formation of Percolative Composites with a High Dielectric Constant and High Conductivity

The dielectric constant and electrical conductivity of a composite of two insulators, poly(1,1-difluoroethylene) (yellow) and K(2)CO(3) (white), increased dramatically near the percolation threshold f(c) (f=concentration of K(2)CO(3)). This intriguing phenomenon can be interpreted in terms of interface percolation caused by the formation of chemically activated interfaces.

Structure and Electrical Properties of (1-x)[(K0.5Na0.5)0.95Li0.05](Nb0.95Sb0.05)O3-xSrTiO3 Lead-Free Piezoelectric Ceramics with Improved Temperature Stability

Lead-free piezoelectric ceramics (1-x)[(K0.5Na0.5)0.95Li0.05](Nb0.95Sb0.05)O3-xSrTiO3 (abbreviated as KNLNS-xST) were sintered by the conventional method. The effects of SrTiO3 content on the structure, the electrical properties and the temperature stability of ceramics were investigated. The X-ray diffraction patterns revealed that all the ceramics have a perovskite structure, and the SEM micrographs revealed that the grain size of the ceramics was decreased with the increase of SrTiO3 content. The partial substitution of SrTiO3 decreased the Curie temperature (Tc) and shifted the orthorhombic–tetragonal phase transition temperature (TO–T) to below room temperature. It was found that the ceramics with x = 0.008 possess optimum piezoelectric properties (d33 = 250 pC/N, kp = 51.7%, ϵr ∼1143 and tanδ ∼ 4.45%), and the ceramics with x = 0.015 exhibit improved temperature stability, due to the shift of TO-T to below room temperature. These results indicate that these materials are promising candidates for lead-free piezoelectric ceramics for practical applications.