Xuhai Li

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.

Enhanced ferroelectric and dielectric properties of highly (100)-oriented 0.67Pb(Mg1/3Nb2/3)O3–0.33PbTiO3 thin films with a special Pb(Zr0.2,Ti0.8)O3/PbOx bilayered buffer layer

0.67Pb(Mg1/3Nb2/3)O3–0.33PbTiO3 (PMN-PT) thin films with a special Pb(Zr0.2,Ti0.8)O3 (PZT)/PbOx bilayered buffer layer have been grown on Pt/Ti/SiO2/Si(100) substrates by rf magnetron sputtering technique. Pure perovskite crystalline phase with highly (100)-preferred orientation, determined by x-ray diffraction, was formed in the PMN-PT thin films. The highly (100)-oriented PMN-PT thin films prepared by using this method possess very good ferroelectric properties with a high remanent polarization Pr (Pr=32 μC/cm2) and a low coercive field Ec (Ec=62 kV/cm). Moreover, the relative dielectric constant as high as 1595 is obtained in the PMN-PT thin films at 1 kHz. The experimental results indicate that the PZT/PbOx buffer layer plays an important role in the crystal orientation, phase purity, and electrical properties of the PMN-PT thin films.

Phase Structure and Electric Properties of BiMeO3 Modified (K0.5Na0.5) NbO3 Lead-Free Ceramics

0.995(K0.5Na0.5)NbO3–0.005 BiMeO3 (Me = Mn, Ga, In, Y, Yb) were successfully prepared by conventional ceramic processing. The effects of low BiMeO3 concentration on crystal structure, dielectric, piezoelectric and ferroelectric properties of the KNN based ceramics were evaluated. The results show that by adding BiMnO3, BiGaO3, and BiInO3 to KNN the structure of the samples showed the orthorhombic phases as the pure KNN. However, by adding BiYO3 or BiYbO3 to KNN a different structure was observed. Adding BiMeO3 to KNN caused the variations of two phase transitions at Tt–o (the temperature at which the phase transition from orthorhombic to tetragonal occurs) and Tc (the Curie temperature). And the variations of P-E loops showed the different effects of BiMeO3 on ferroelectric properties.

Effects of Mg on the Microstructure and Electrical Properties of (K0.5Na0.5)NbO3-LiSbO3 Lead-free Ceramics

Lead-free piezoelectric ceramics, Mg substituted (K0.5Na0.5)NbO3-LiSbO3, have been fabricated by using conventional mixed-oxide method with sintering temperature of 1080∼1120°C. The crystal structure and microstructure of the ceramics were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The effect of Mg substitution on the microstructure of the ceramics was discussed. The results reveal that the ceramics possess an orthorhombic perovskite structure, and a small amount of Mg substitution is very effective in promoting the densification of the ceramics. The effect of Mg substitution on the dielectric, and piezoelectric properties of the ceramics was also investigated.

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.

Phase Structure and Electrical Properties of Lead-Free (K0.5 Na0.5)NbO3-YMnO3 Ceramics

Lead-free piezoelectric ceramics (1-x) (K0.5Na0.5)NbO3-xYMnO3 (KNNYM) have been fabricated by using conventional sintering technique. The structure, dielectric and piezoelectric properties of the KNNYM ceramics were investigated. It was found that the ceramics possess orthorhombic structure at room temperature, and have high Curie temperature (TC > 400°C). The increase of YMnO3 (0 < x ≤ 0.06) additives is very effective in improving the mechanical quality factors (Qm) of the ceramics, and the temperature of the orthorhombic to tetragonal phase transition (TO − T) also increases, however, a secondary phase could be found in the ceramics when x ≥ 0.02.