Tian-Fu Zhang

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 ...

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.

High Energy Storage Density and Impedance Response of PLZT2/95/5 Antiferroelectric Ceramics

(Pb0.97La0.02)(Zr0.95Ti0.05)O3 (PLZT2/95/5) ceramics were successfully prepared via a solid-state reaction route. The dielectric properties were investigated in the temperature region of 26–650 °C. The dielectric diffuse anomaly in the dielectric relaxation was found in the high temperature region of 600–650 °C with increasing the measuring frequency, which was related to the dynamic thermal process of ionized oxygen vacancies generated in the high temperature. Two phase transition points were detected during heating, which were found to coexist from 150 to 200 °C. Electric field induced ferroelectric to antiferroelectric phase transition behavior of the (Pb0.97La0.02)(Zr0.95Ti0.05)O3 ceramics was investigated in this work with an emphasis on energy storage properties. A recoverable energy-storage density of 0.83 J/cm3 and efficiency of 70% was obtained in (Pb0.97La0.02)(Zr0.95Ti0.05)O3 ceramics at 55 kV/cm. Based on these results, (Pb0.97La0.02)(Zr0.95Ti0.05)O3 ceramics with a large recoverable energy-storage density could be a potential candidate for the applications in high energy-storage density ceramic capacitors.

Switching Characteristics and High-Temperature Dielectric Relaxation Behaviours of Pb(Zn1/3Nb2/3)0.91Ti0.09O3 Single Crystal

This work evaluated the resistance switching characteristics in the (100)-oriented Pb(Zn1/3Nb2/3)0.91Ti0.09O3 (PZNT) single crystal. The current hysteresis can be closely related to the ferroelectric polarization and we provided a possible explanation using a model about oxygen vacancies to analyze the mechanism of switching. The obvious frequency dispersion of the relative permittivity signified the relaxer-type behavior of the sample. The value of the relaxation parameter γ = 1.48 was estimated from the linear fit of the modified Curie-Weiss law, indicating the relaxer nature. High-temperature dielectric relaxation behaviors were revealed in the temperature region of 400–650 °C. In addition, under the measuring frequency of 10 kHz, εr was tunable by changing the electric field and the largest tunability of εr reached 14.78%. At room temperature, the high pyroelectric coefficient and detectivity figure of merit were reported.

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.