Zupei Yang

Phase transitional behavior and electrical properties of lead-free (K0.44Na0.52Li0.04)(Nb0.96−xTaxSb0.04)O3 piezoelectric ceramics

Lead-free (K0.44Na0.52Li0.04)(Nb0.96−xTaxSb0.04)O3 piezoelectric ceramics have been synthesized by conventional solid state sintering process. Two morphotropic phase boundaries (MPBs) respectively corresponding to the orthorhombic to tetragonal and tetragonal to pseudocubic phases are observed with increasing x. The ceramics with x=0.20 between the two MPBs show significantly enhanced electrical properties, which are as follows: piezoelectric constant d33=252pC∕N, planar coupling coefficient kp=0.42, dielectric constant er=1503, and dielectric loss tanδ=0.025, and they show good stability. Lead-free superthin buzzer disks have been prepared by using piezoceramic membrane with x=0.20. (K0.44Na0.52Li0.04)(Nb0.96−xTaxSb0.04)O3 ceramics are very promising as lead-free replacements for lead zirconate titanate.

⟨001⟩ textured (K0.5Na0.5)(Nb0.97Sb0.03)O3 piezoelectric ceramics with high electromechanical coupling over a broad temperature range

⟨001⟩-oriented (K0.5Na0.5)(Nb0.97Sb0.03)O3 (KNNS) ceramics with a narrow orientation distribution (full width at half maximum=7.0°) were produced by templated grain growth using NaNbO3 templates. Excellent electromechanical properties were obtained from −70 °C to the polymorphic phase transition (PPT) at 160 °C. Textured KNNS ceramics show very high electromechanical coupling factors kp=0.64 and k31=0.37, high piezoelectric constants d33=208–218 pC/N and d31=−82 pC/N, and modest strain hysteresis (6.3%) at room temperature. These properties are superior to those of randomly oriented KNN-based ceramics with similar PPT temperatures.

Effects of Li content on the phase structure and electrical properties of lead-free (K0.46−x∕2Na0.54−x∕2Lix)(Nb0.76Ta0.20Sb0.04)O3 ceramics

Lead-free (K0.46−x∕2Na0.54−x∕2Lix)(Nb0.76Ta0.20Sb0.04)O3 piezoelectric ceramics were prepared by the conventional solid state sintering method without cold-isostatic pressing process. The x-ray diffraction and Raman scattering results show that the phase structure of the ceramics undergoes a transition from pseudocubic to tetragonal phase with increasing x from 0 to 0.10. Significantly enhanced electrical properties (d33=259pC∕N, kp=0.42, er=1653, and tan δ=0.027) were obtained in the ceramics with x=0.04 near the morphotropic phase boundary, and only the tetragonal-cubic phase transition was observed above the room temperature in the er-T curve. The temperature stability of the ceramics with x=0.04 was also investigated.

Phase transitional behavior, microstructure, and electrical properties in Ta-modified [(K0.458Na0.542)0.96Li0.04] NbO3 lead-free piezoelectric ceramics

Lead-free [(K0.458Na0.542)0.96Li0.04] (Nb1−xTax)O3 ceramics were prepared by ordinary sintering technique. The effects of Ta content on the phase transitional behavior, Raman spectrum, microstructure, and dielectric, piezoelectric, and ferroelectric properties of the ceramics were investigated. X-ray diffraction results indicate that the phase structure undergoes a transition from orthorhombic to tetragonal phase with the increase in x. The small and large peaks observed in the Raman spectra can all be attributed to the internal modes of the NbO6 octahedron, and both ν5 and ν1 modes slightly shift to lower frequency numbers by increasing x. Ta substitution for Nb leads to the disappearance of the abnormal grain growth behavior, inhibits the grain growth, and improves the density of the ceramics. Increasing x leads to the different variations of dielectric constants before and after poling and makes the ceramics more relaxorlike. The proper substitution of Ta shifts the polymorphic phase transition (at To-...

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.

Phase coexistence and high electrical properties in (KxNa0.96−xLi0.04)(Nb0.85Ta0.15)O3 piezoelectric ceramics

(KxNa0.96−xLi0.04)(Nb0.85Ta0.15)O3 lead-free piezoelectric ceramics were produced by conventional solid-state reaction method. The effects of K/Na ratio on the phase transitional behavior, Raman spectrum, microstructure, and dielectric, piezoelectric, and ferroelectric properties of the ceramics have been investigated. The phase structure of the ceramics undergoes a transition from orthorhombic to tetragonal phase with increasing x. A double-degenerate symmetric O–Nb–O stretching vibration v1 and a triply degenerate symmetric O–Nb–O bending vibration v5 are detected as relatively strong scattering in the Raman spectra. The peak shifts of v5 and v1 modes all have a discontinuity with x between 0.42 and 0.46, which may suggest the coexistence of orthorhombic and tetragonal phases in this range. Properly modifying x reduces the sintering temperature, promotes the grain growth behavior, and improves the density of the ceramics. The polymorphic phase transition (at To-t) is shifted to near room temperature by ...

Origin of giant permittivity and high-temperature dielectric anomaly behavior in Na0.5Y0.5Cu3Ti4O12 ceramics

Na0.5Y0.5Cu3Ti4O12 ceramics prepared by the conventional solid-state reaction method under various sintering conditions were found to exhibit a giant dielectric constant over 10 000 around room temperature. Two electrical responses were observed in the combined modulus and impedance plots, indicating the presence of Maxwell-Wagner relaxation. The contributions of semiconducting grains and insulating grain boundaries (corresponding to high-frequency and low-frequency electrical response, respectively) played important roles in the dielectric properties of Na0.5Y0.5Cu3Ti4O12 ceramics. The correlations between grain boundaries resistance and low frequency dielectric loss, grains resistance and the position of dielectric loss peak were addressed. Mixed-valent structures of Cu2+/Cu3+ and Ti3+/Ti4+ had been determined using X-ray photoelectron spectroscopy. Electron hopping between Cu2+ and Cu3+ and electron transport in Ti3+–O–Ti4+ paths were proposed as the origin of the semiconducting nature of Na0.5Y0.5Cu3T...

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.

Preparation and capacitance property of MnO2-pillared Ni2+–Fe3+ layered double hydroxides nanocomposite

A novel MnO(2)-pillared Ni(2+)-Fe(3+) layered double hydroxides nanocomposite has been successfully fabricated using an intercalation/reduction reaction followed by heating treatment. The structural evolution of the samples obtained at different stages has been characterized by XRD, TEM, XPS, IR and N(2) adsorption-desorption. The layered structure of MnO(2)-pillared Ni(2+)-Fe(3+) layered double hydroxides nanocomposite can be maintained at 300 °C, and the obtained material has a large surface area of 202 m(2) g(-1). Electrochemical studies indicate that the material obtained by heating at 200 °C exhibits an ideal capacitive behavior and good cycling property in 1 mol L(-1) Na(2)SO(4) aqueous solution, and the specific capacitance value was 190 F g(-1) at a scan rate of 5 mV s(-1).

Sintering behavior and refining grains of high density tin doped indium oxide targets with low tin oxide content

High density indium tin oxide (ITO) ceramic targets with low SnO2 content were prepared successfully by sintering co-precipitationally synthesized powders. The sintering behavior, properties and refining grains of the ITO targets were studied in normal pressure oxygen ambience. Higher sintering temperature promoted sintering densification, resulted in abnormal grain growth and decreased bending strength. By a two-step sintering method, the uniform and fine-grained microstructures were obtained. The sintered density of the ITO targets was further improved. Furthermore, the grain size was reduced, and the bending strength was also enhanced.