Faqiang Zhang

Large piezoelectric properties in KNN-based lead-free single crystals grown by a seed-free solid-state crystal growth method

This work was supported by the National Natural Science Foundation of China (NSFC, Nos. 51332009 and 51172257), National Basic Research Program of China 973- Projects (2012CB619406), the CAS/SAFEA International Partnership Program for Creative Research Teams, and Science and Technology Commission of Shanghai Municipality (15ZR1445400). Y.L. appreciates the financial support from the Australian Research Council in the form of Future Fellowship.

Tetrahedral amorphous-carbon thin films for silicon-on-insulator application

The application of a silicon-on-insulator substrate in a high-power integrated circuit is limited by the self-heating effect, caused by the poor thermal conductivity of the buried SiO2. We introduce tetrahedral amorphous-carbon thin films, formed by the filtered arc deposition method, as an alteration. We investigated the surface morphology, microstructure, and electrical properties of these films. The films deposited under a substrate bias of −200 V displayed outstanding surface topography (low surface roughness with the Rrms value under 0.5 nm) and excellent electrical property (breakdown field of 4.7 MV/cm). The film has a high content of sp3 bonds of carbon (87%) and low content of oxygen (<2%).

Fabrications and Performance of Wireless LC Pressure Sensors through LTCC Technology

This paper presents a kind of passive wireless pressure sensor comprised of a planar spiral inductor and a cavity parallel plate capacitor fabricated through low-temperature co-fired ceramic (LTCC) technology. The LTCC material with a low Young’s modulus of ~65 GPa prepared by our laboratory was used to obtain high sensitivity. A three-step lamination process was applied to construct a high quality cavity structure without using any sacrificial materials. The effects of the thickness of the sensing membranes on the sensitivity and detection range of the pressure sensors were investigated. The sensor with a 148 μm sensing membrane showed the highest sensitivity of 3.76 kHz/kPa, and the sensor with a 432 μm sensing membrane presented a high detection limit of 2660 kPa. The tunable sensitivity and detection limit of the wireless pressure sensors can meet the requirements of different scenes.

Enhanced energy storage properties of barium titanate ceramics made from surface modified particles

Surface modification of barium titanate particles has been carried out using a wet chemical method. The microstructural and dielectric properties of the ceramics made from surface modified particles were extensively investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and dielectric properties measurements. The breakdown strength increased by 69% and 117% for the Al2O3 and B2O3–SiO2 modified ceramics, respectively. An energy storage density of up to 3.2 J/cm3 has been obtained. The suppression of grain boundary electron transport and reduction in pore defects lead to the energy storage properties enhancement of the modified ceramics. These results indicated that surface modification of ceramic particles is a promising approach to obtain dielectric ceramics with high energy storage density.

Colossal permittivity and the polarization mechanism of (Mg, Mn) co-doped LaGaO3 ceramics

Mg and Mn co-doped LaGa0.7-xMgxMn0.3O3 (x = 0, 0.05, 0.10, 0.15) ceramics were prepared by a solid-state reaction method. The electrical properties of the LaGa0.7-xMgxMn0.3O3 ceramics were studied in detail by dielectric spectra, impedance spectra, and I-V characteristic analysis. Colossal permittivity up to 104 could be obtained across the frequency range up to 104 Hz. The impedance analysis of the co-doped LaGaO3 ceramics indicated that the Motts variable range hopping (VRH) polarization should be the main origin of colossal permittivity. Mg and Mn co-doping suppressed the formation of Mn3+ and enhanced the VRH polarization, resulting in increased permittivity. Partial localization of electrons by Mg reduced the long-range electron hopping and led to the decrease in dielectric loss.

Anomalous Photovoltaic Effect in Centrosymmetric Ferroelastic BiVO4

The anomolous photovoltaic (APV) effect is an intriguing phenomenon and rarely observed in bulk materials that structurally have an inversion symmetry. Here, the discovery of such an APV effect in a centrosymmetric vanadate, BiVO4, where noticeable above-bandgap photovoltage and a steady-state photocurrent are observed in both ceramics and single crystals even when illuminated under visible light, is reported. Moreover, the photovoltaic voltage can be reversed by the stress modulation, and a sine-function relationship between the photovoltage and stress directional angle is derived. Microstructure and strain-field analysis reveal localized asymmetries that are caused by strain fluctuations in bulk centrosymmetric BiVO4. On the basis of the experimental results, a flexoelectric coupling via a strain-induced local polarization mechanism is suggested to account for the APV effect observed. This work not only allows new applications for BiVO4 in optoelectronic devices but also deepens insights into the mechanisms underlying the APV effect.

Synthesis of Intergrowth Bi7Ti4NbO21 Compound by Sol-Gel Method and Its Comparison with Other Synthesis Methods

Intergrowth Bi7Ti4NbO21 (iBTN) was synthesized by sol-gel, solid state and co-precipitation method. Their morphology and phase were analyzed. It was found that using sol-gel method, iBTN was observed to already formed at temperature as low as 550°C. This opens up the possibility of using sol-gel method to synthesize other complex intergrowth material which may have various interesting properties.

Dielectric Behavior of (Ba0.95Ca0.05)(Zr0.15Ti0.842Mg0.008)O3- (Ba0.95Ca0.05)(Zr0.08Ti0.92)O3 Layered Ceramics

(Ba0.95Ca0.05)(Zr0.15Ti0.842Mg0.008)O3-(Ba0.95Ca0.05)(Zr0.08Ti0.92)O3 (MBZT-BZT) composite with layered structure (2-2 model) were fabricated by tape-casting and lamination technique. The ceramics with different thickness of single layer were prepared and studied. All of ceramics are composites with clear layered structure. Dielectric bi-shoulders measured in the direction of parallel and perpendicular to the interface of two layers are not completely in conformity with theoretical results. And they shifted towards opposite compared with the theoretical results due to the idealization of theoretical simulation and the change of microstructure. Complex impedance spectra indicated that the impact of interfacial polarization exiting at in inter-phase boundaries were weakly.