Browsing by Author "Wang, Ningzhang"

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    Electrocaloric effect in La-doped BNT-6BT relaxor ferroelectric ceramics
    (Elsevier, 2017-09-22) Li, Lucheng; Xu, Mengxing; Zhang, Qi; Chen, Ping; Wang, Ningzhang; Xiong, Dingkang; Peng, Biaolin; Liu, Laijun
    Relaxor [(Bi1/2Na1/2)0.94Ba0.06](1-1.5x)LaxTiO3 (x = 0, 0.03, 0.06, 0.09) ceramics (La-doped BNT-6BT) with composition close to the morphotropic phase boundary (MPB) were successfully prepared by using the conventional solid state reaction method. All samples present almost a pure perovskite phase with the coexistence of tetragonal and rhombohedral. With the increase of La doping content, the degree of the dielectric relaxor dispersion around the dielectric peak which is close to the room temperature increases, and also the transition temperature of ferroelectric-to-relaxor (TF-R) shifts 120 K towards a lower temperature at x = 0.09. The maximum value of the temperature change (ΔT) of the electrocaloric (EC) effect decreases sharply from 1.1 K at x = 0–0.064 K at x = 0.09. A large positive EC effect (maximum ΔT ~ 0.44 K) in a broad temperature range (~ 90 K) close to room temperature is achieved at x = 0.03, indicating that it is a promising lead-free material for application in solid state cooling system. Moreover, it is found that the Maxwell relationship can be well used to assess the EC effects of the La-doped BNT-6BT ceramics when the operating temperature is higher than that of the TF-R, indicating that these relaxor ceramics would perform as an ergodic.
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    High-performance La-doped BCZT thin film capacitors on LaNiO3/Pt composite bottom electrodes with ultra-high efficiency and high thermal stability
    (Elsevier, 2019-03-13) He, Shangkai; Peng, Biaolin; Leighton, Glenn J. T.; Shaw, Christopher; Wang, Ningzhang; Sun, Wenhong; Liu, Laijun; Zhang, Qi
    Dielectric capacitors possessing large energy storage density, high efficiency and high thermal stability simultaneously are very attractive in modern electronic devices to be operated in harsh environment. Here, it is demonstrated that large energy storage density (W ∼ 15.5 J/cm3), ultra-high efficiency (η ∼93.7%) and high thermal stability (the variation of both W from 20 °C to 260 °C and η from 20 °C to 140 °C is less than 5%) have been simultaneously achieved in the La-doped (Ba0.904Ca0.096)0.9775+xLa0.015(Zr0.136Ti0.864)O3 (x = 0.0075) lead-free relaxor ferroelectric thin film capacitors deposited on LaNiO3/Pt composite bottom electrodes by using a sol-gel method. The good energy storage property of the thin film capacitors at x = 0.0075 is mainly ascribed to the diversity of the structure of the nano-clusters around the three-phases coexisting component point (Ba0.904Ca0.096)(Zr0.136Ti0.864)O3 where cubic, tetragonal and rhombohedral phases coexisted, as well as the ultra-high quality of thin film due to the utilization of the LaNiO3/Pt composite bottom electrode, making it a promising candidate for dielectric capacitors working in harsh environments.