Xin-Gui Tang

Oxygen-vacancy-related relaxation and conduction behavior in (Pb1-xBax)(Zr0.95Ti0.05)O3 ceramics

(Pb1-xBax)(Zr0.95Ti0.05)O3 (x = 0, 0.025, 0.05, 0.075 and 0.1) ceramics were prepared via a solid-state reaction route. Low-frequency (20 ∼ 2 × 107 Hz) dielectric properties were investigated in the temperature region of 25-650 °C. Ba2+ doping can slightly reduce the phase transition temperature of ferroelectric to paraelectric. The dielectric diffuse anomaly in the dielectric relaxation was found in the high temperature region of 400-650 °C. Activation energy, calculated from the impedance and conductivity data of samples, suggests that the dielectric relaxation is due to oxygen vacancies generated during the sintering process. Ba2+ doping can reduce significantly the concentration of oxygen vacancies, and slightly enhance activation energy for the migration of oxygen vacancies. Results of activation energy calculated from impedance and conductance suggest that the dielectric relaxation is due to the short-range hopping of oxygen vacancies, and the conduction due to the movement of doubly-ionized oxygen ...

Structure and composition-dependent optical properties of (PbxSr1–x)TiO3 (x=0.4, 0.6) nanotube arrays

Abstract Lead strontium titanate (PbxSr1–x)TiO3 (x=0.4, 0.6) nanotubes were synthesized by sol-gel template method via spin coating. The structures and morphology of the as-prepared samples were characterized by X-ray diffractometry, scanning electron microscopy and transmission electron microscopy. X-ray photoelectron spectroscopy was used to determine the chemical composition of the sample and the valence state of elements. Raman spectroscopy of the as-prepared (PbxSr1–x)TiO3 (x=0.4, 0.6) nanotubes at room temperature was also investigated. The results indicate that as-prepared (PbxSr1–x)TiO3 (x=0.4, 0.6) nanotubes are perfectly crystallized and there is a trend of structure change from PST40 to PST60. A weak peak at 508 cm−1 assigned to E(3TO) mode can be seen in the Raman spectrum of (Pb0.6Sr0.4)TiO3 sample. Photoluminescence spectra of samples at room temperature reveal three intense emission bands centered at 356, 400 nm for (Pb0.4Sr0.6)TiO3 and 413, 433, 451 nm for (Pb0.6Sr0.4)TiO3 nanotubes, respectively. The peak positions of the emission band have a significant blue shift as Pb content increases.

Antiferroelectric to relaxor ferroelectric phase transition in PbO modified (Pb0.97La0.02)(Zr0.95Ti0.05)O3 ceramics with a large energy-density for dielectric energy storage

(Pb0.97(1+x)La0.02)(Zr0.95Ti0.05)O3 (PLZT2/95/5) ceramics with excess lead content (x = 0, 3%, 5%, 7.5%, 10% and 15%) were successfully prepared via a solid-state reaction route. X-ray diffraction analysis indicated that a pure perovskite structure was obtained for all compositions. The effects of excess lead content on the microstructure, dielectric properties, and energy-storage performance of PLZT2/95/5 ceramics were systematically investigated. The ceramics exhibited tetragonal phase structures and showed two dielectric peaks at 120 and 240 °C, corresponding to antiferroelectric–ferroelectric and ferroelectric–paraelectric phase transitions. The recoverable energy-storage density calculated from hysteresis loops reached about 2.12 J cm−3 with an efficiency of 92.98%, which was due to the phase transition from the antiferroelectric state to the relaxor ferroelectric state. Based on these results, typical PLZT2/95/5 ceramics with different lead excess content have been studied, which could be potential candidates for applications in high energy storage-density electrical capacitors.

Improvement of electrical conductivity and leakage current in co-precipitation derived Nd-doping BiFeO3 ceramics

Abstract BiFeO3 and Bi0.925Nd0.075FeO3 ceramics were prepared by co-precipitation method. The crystal structure and electrical properties of the samples were characterized by X-ray diffraction (XRD), impedance spectra and leakage current measurement. XRD result implied that the impurity phases are weakened by suitably doping Nd. The impedance spectra of BiFeO3 sample indicate that low grain boundary resistance and non Debye-type relaxation below the Néel temperature. Complex impedance spectra suggested that the doped samples are closer to Debye-type, and the grain boundary resistance increases which lead to low leakage current density.

X-Ray Photoelectron Spectroscopy of (La0.7Sr0.3)MnO3Thin Films Prepared by Pulsed Laser Deposition

(La0.7Sr0.3)MnO3 (LSMO) thin films were grown on Si (100) substrate by using pulsed laser deposition (PLD) process. Both structure and surface morphology of the films were investigated by X-ray diffraction (XRD) and atomic force microscopy (AFM). Furthermore, the chemical states and chemical composition of the films were determined by X-ray photoelectron spectroscopy (XPS) near the surface. From XRD, the results indicate that the films grown on Si (100) substrates have a single pseudocubic perovskite phase structure with a high (100) orientation. The XPS results show that La, Sr and Mn exist mainly in the forms of perovskite structure and a SrO layer was found on outermost surface. The films resistivity emeasured under room temperature is 6.4´10-4 W×cm.

High frequency single crystal ultrasonic transducers up to 100 MHz for high resolution ophthalmic imaging applications

As one of the most important and well established tools, ultrasound imaging provides noninvasive valuable diagnostic information, especially in the form of cross-sectional images of soft tissues. High frequencies are used directly to enable high resolution imaging to be of clinical benefit. As a result, high-frequency ultrasonic transducers with better resolution are needed. The difficulty of a high frequency transducer comes from preparation of a very thin layer of piezoelectric material with piezoelectric properties similar to bulk material. To date, although there are some reports about high frequency (80 to 100 MHz) ultrasonic transducers for eye imaging applications, but the focal length of those transducers are not enough and the images are not clear enough. In this work, high frequency transducers were prepared and used for eye imaging, high resolution of pig eye imaging were obtained.

Electrocaloric effect in BaTiO 3 based lead-free multilayer ceramic capacitors

The electrocaloric effect (ECE) of multilayer ceramic capacitor (MLCC) of Y5V type was directly measured via a differential scanning calorimetry (DSC) method and a reference resistor was used to calibrate the heat flow due to the heat dissipation. The results are compared with those calculated from Maxwell relations by using the polarization data obtained from the polarization - electric field hysteresis loops. The direct method shows a larger ECE temperature change, which is accounted for the situation approaches an ideal condition. For the indirect method using Maxwell relations, only the polarization projection along the electric field was taken into account, which will be less than the randomly distributed real polarizations that contribute to the ECE. The MLCCs exhibit a broad peak of ECE around 80 °C, which will be favorite for the practical ECE cooling devices.