Xiaolian Chao

Polymorphic structure evolution and large piezoelectric response of lead-free (Ba,Ca)(Zr,Ti)O3 ceramics

The polymorphic structure evolution of (Ba,Ca)(Zr,Ti)O3 piezoelectric ceramics was investigated by analysis of the in situ X-ray diffraction and dielectric spectra. The results indicated that a confined orthorhombic (O) phase region induced by the approach of the rhombohedral (R) and tetragonal (T) phases existed in an extremely narrow temperature range of (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 composition. The electric properties near the O–T phase boundaries of (Ba0.95Ca0.05)(Zr0.05Ti0.95)O3 and (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 were compared. The results suggested that the confined O phase region is an important factor that contributes to the extremely large piezoelectric response.

Low dielectric loss, dielectric response, and conduction behavior in Na-doped Y2/3Cu3Ti4O12 ceramics

The Na-doped Y2/3Cu3Ti4O12 system has been prepared and investigated. Na doping facilitates the formation of oxygen vacancies, which is of great benefit to the growth of the grain size. Proper amount of Na substitution in NaxY(2−x)/3Cu3Ti4O12 ceramics makes the dielectric loss significantly decreased. As x = 0.050, Na0.050Y0.650Cu3Ti4O12 ceramics exhibit the lowest dielectric loss (about 0.022 at 1 kHz) and a relatively high dielectric constant (about 7500 at 1 kHz). The lowered dielectric loss is closely associated with the enhanced resistance of grain boundary. The conduction and dielectric processes of grain boundary become much more difficult after Na doping. Impedance analysis suggests that the same charge defects are responsible for the conduction and dielectric relaxation behaviors of grain boundary. Scaling behaviors indicate that the physical nature of their dielectric relaxation and conduction behavior are independent of the measurement temperature and the Na concentration.

Effect of Sintering Process on Characteristics of Multilayer Piezoelectric Pb(Mg1/3Nb2/3)O3?Pb(Zn1/3Nb2/3)O3?Pb(Zr,Ti)O3 Ceramic Transformers

Multilayer piezoelectric transformers are fabricated as 2:2:1-type transformers with dimensions 30.0 mm length × 6.0 mm width × 3.4 mm thickness. Much attention has been focused on the characteristics and applications of Pb(Mg1/3Nb2/3)O3–Pb(Zn1/3Nb2/3)O3–Pb(Zr,Ti)O3 (PMN–PZN–PZT)-based multilayer piezoelectric transformers (MPTs) formed at various calcining and sintering temperature. The characteristics of MPTs, including the step-up ratio, efficiency and temperature rise with input voltage and driving frequency, are systemically investigated. The results show that the piezoelectric transformers calcined at 800 °C and sintered at 1020 °C exhibit the favorable characteristics with a high step-up ratio, a favorable efficiency and a low temperature rise.

Enhanced transmittance and piezoelectricity of transparent K0.5Na0.5NbO3 ceramics with Ca(Zn1/3Nb2/3)O3 additives

Considering the environment and human health, highly transparent lead-free (1 − x)K0.5Na0.5NbO3–xCa(Zn1/3Nb2/3)O3 (abbreviated as KNN–xCZN) piezoceramics were synthesized by a solid state reaction method. The effects of Ca(Zn1/3Nb2/3)O3 on the microstructures, phase structures, characteristic frequency and electrical properties were investigated. Fine grain and relaxor-like behaviors were obtained, and the Ca(Zn1/3Nb2/3)O3 also increased the crystal structure of the ceramics transformation from orthorhombic to pseudo-cubic. It was found that the highest transmittance of 70.42% (with a thickness of 0.5 mm in the visible spectrum) was obtained for the KNN–xCZN ceramics at x = 0.07, which was due to the high relative density, low apparent porosity, uniform and fine-grained microstructures, high symmetry of the pseudo-cubic structure, NbO6 octahedron reduced distortion and more relaxor-like behavior. In addition, the transparent piezoelectric ceramics KNN–xCZN with x = 0.07 possessed high transmittance (∼84% at near-infrared wavelengths) and excellent electrical properties (er = 1162, d33 = 102 pC N−1). All of the above demonstrated that the KNN–xCZN ceramics could be promising lead-free transparent piezoceramics.

Diffusion phase transition and impedance spectroscopy of Bi2O3/CuO co-doped BCZT lead-free ceramics

Perovskite type (Ba0.85Ca0.15−2xBi2x)(Zr0.1Ti0.9−xCux)O3 lead-free ceramics were prepared via a conventional solid-state reaction method. The phase structure, dielectric, ferroelectric properties and complex impedance were investigated in detail. XRD and dielectric measurements determined that single orthorhombic phase displayed in (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 at room temperature. With the introduction of Bi2O3/CuO, the phase structure exhibited the mixture of orthorhombic and tetragonal phases, and then turned to single tetragonal phase. In contrast to the sharp dielectric transition of (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 ceramics, a broad dielectric peak coupled with a slight decrease in Curie temperature was observed in (Ba0.85Ca0.15−2xBi2x)(Zr0.1Ti0.9−xCux)O3 ceramics with increasing x. The observed diffuse phase transition behavior was further confirmed by a couple of measurements with polarization loops and polarization current density curves. The structural and the composition fluctuations induced by ions doping should be responsible for the diffuse phase transition behavior. Furthermore, physical mechanisms of the conduction and relaxation processes were revealed by using impedance spectroscopy analyses. It was concluded that the conduction and relaxation processes were thermally activated, which was closely linked with the singly and doubly ionized oxygen vacancies.

Effect of Carbon Nanotubes on the Structure, Internal Loss Storage, and Damping–Absorption Properties of CNT/PZT/RTV

ABSTRACT Composites with damping–absorption performance and storage-loss behavior based on carbon nanotubes as a modifier and zinc titanate/room temperature vulcanized silicone rubbers as a matrix were fabricated by a reactive solution mixing process, wet ball milling, and the three-roller milling method. The microstructures, chemical structures, and morphologies of the composites were characterized by scanning electron microscopy, infrared spectroscopy, and X-ray diffraction. The thermal stabilities were investigated by thermogravimetric analysis. The effect of carbon nanotubes on the comprehensive performance of the carbon nanotube/zinc titanate/room temperature vulcanized silicon rubber composites was investigated. It was found that doping with carbon nanotubes can improve the comprehensive performance of the zinc titanate/room temperature vulcanized silicon rubber complex matrix. The best comprehensive properties were d33 = 72 pC/N, storage modulus = 4,100 MPa, loss modulus = 400 MPa, damping coefficient = 0.23, and absorption coefficients = 0.4–0.6 for 4 wt% carbon nanotube/zinc titanate/room temperature vulcanized silicon rubber. In addition, the lattice parameters of zinc titanate were found to be highly dependent on the carbon nanotube content, and the absorption and damping performance of the composites were dependent on the frequency and temperature. GRAPHICAL ABSTRACT