Browsing by Author "Zhang, Qingfeng"

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    Bismuth ferrite materials for solar cells: Current status and prospects
    (Elsevier, 2018-10-09) Chen, Guang; Chen, Jian; Pei, Weijie; Lu, Yinmei; Zhang, Qingfeng; Zhang, Qi; He, Yunbin
    Different from classical semiconductor photovoltaic devices, for ferroelectric photovoltaic devices, the open-circuit voltage (Voc) can be four and even more orders of magnitude larger than the band gap of the ferroelectric, and the built-in electric field arising from the remnant polarization of the ferroelectric is throughout the bulk region, which is good for obtaining giant power conversion efficiency. Among ferroelectric materials, BiFeO3 with remnant polarization of as high as ∼100 μC/cm2 has the narrowest direct band gap (∼2.7 eV). These indicate that high power conversion efficiency may be obtained in BiFeO3-based photovoltaic devices. Also, some significant research results about photovoltaic effects of BiFeO3 materials have been recently acquired. In order to better promote the development of BiFeO3-based photovoltaic devices, in this paper, we present a comprehensive review on the latest research progress in photovoltaic effects of BiFeO3 materials with different kinds of topography, including bulk, thin film, and nanomaterials.
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    Exploration on the origin of enhanced piezoelectric properties in transition-metal ion doped KNN based lead-free ceramics
    (Elsevier, 2018-06-12) Xu, Fang; Chen, Jian; Lu, Yinmei; Zhang, Qingfeng; Zhang, Qi; Zhou, Taosheng; He, Yunbin
    In this work, we studied effects of Ni2O3 and Co2O3 doping on crystal structures, microstructures, orthorhombic and tetragonal phase transition temperature (To-t), and electrical properties of [Li0.06(Na0.57K0.43)0.94][Ta0.05(Sb0.06Nb0.94)0.95]O3 (LNKTSN) lead-free ceramics. The experimental results showed that the Ni2O3 addition with appropriate amount could shift the To-t downwards to the room temperature, and thus obviously increasing the room-temperature piezoelectric coefficient (d33), dielectric coefficient (εr) and electromechanical coupling coefficient (kp) of the LNKTSN ceramics. These were consistent with previous experimental results obtained in Fe2O3 doped LNKTSN ceramics. On the contrary, Co3+ doping shifted continuously the To-t upward and deteriorated obviously piezoelectric properties of LNKTSN ceramics. Fe, Co and Ni had similar ion radii and were expected to result in the same (donor or acceptor) doping effects on electrical properties of LNKTSN ceramics. The different doping effects between Co3+ (deterioration) and Ni3+ or Fe3+ (improvement) on the electrical properties of LNKTSN ceramics suggested that the coexistence of orthorhombic and tetragonal phases at room temperature due to downward shift of To-t, rather than ion doping (donor or acceptor doping) effects was the main cause for enhanced room-temperature piezoelectric properties. This conclusion can be extended to all KNN-based materials in general, thus offering principle guide for future development of new lead-free materials with good piezoelectric properties.
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    High energy density of PLZST antiferroelectric ceramics prepared by sol-gel method with low-cost dibutyltin oxide
    (Wiley, 2018-08-31) Dan, Yu; Xu, Haojie; Zhang, Yangyang; Zou, Kailun; Zhang, Qingfeng; Lu, Yinmei; Chang, Gang; Zhang, Qi; He, Yunbin
    Lead lanthanum zirconate stannate titanate (PbLa(ZrSnTi)O3) antiferroelectric (AFE) ceramics are widely used in dielectric capacitors due to their superior energy‐storage capacity. Generally, these ceramics can be synthesized by solid‐state reaction and sol‐gel methods. Ceramics prepared using the sol‐gel method have a purer phase than those prepared using the solid‐state reaction method because the sol‐gel method can avoid the segregation of Sn. However, because the commonly used raw material tin acetate is very expensive, the preparation of PbLa(ZrSnTi)O3 AFE ceramics via the sol‐gel method is not cost‐effective, which prevents the use of sol‐gel method for manufacturing PbLa(ZrSnTi)O3 in a large scale. In this work, low‐cost dibutyltin oxide instead of expensive tin acetate is used to synthesize Pb0.97La0.02(Zr0.50Sn0.45Ti0.05)O3 (PLZST) nanopowders, and single‐phase powders with a perovskite structure and average grain size of 200 nm are obtained at a calcination temperature of 580°C. In addition, dense PLZST AFE ceramics with a pure perovskite structure are obtained by sintering the PLZST nanopowders at temperatures as low as 1100°C. The sintered PLZST ceramics exhibit a room‐temperature recoverable energy‐storage density as high as 1.93 J/cm3 with an efficiency of 75%, which varies only slightly in the temperature range of 20‐120°C. The high energy‐storage density (>1.9 J/cm3) over a wide temperature range illustrates that the sol‐gel‐derived PLZST ceramics with low‐cost dibutyltin oxide are quite promising for manufacturing pulse power capacitors.
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    Superior energy-storage properties in (Pb,La)(Zr,Sn,Ti)O-3 antiferroelectric ceramics with appropriate La content
    (Elsevier, 2019-03-06) Dan, Yu; Zou, Kailun; Chen, Guang; Yu, Yuxi; Zhang, Ying; Zhang, Qingfeng; Lu, Yinmei; Zhang, Qi; He, Yunbin
    Antiferroelectric (AFE) ceramics based on Pb(Zr,Sn,Ti)O3 (PZST) have shown great potential for applications in pulsed power capacitors because of their fast charge-discharge rates (on the order of nanoseconds). However, to date, it has been proven very difficult to simultaneously obtain large recoverable energy densities Wre and high energy efficiencies η in one type of ceramic, which limits the range of applications of these materials. Addressing this problem requires the development of ceramic materials that simultaneously offer a large ferroelectric-antiferroelectric (FE-AFE) phase-switching electric field EA, high electric breakdown strength Eb, and narrow polarization-electric field (P-E) hysteresis loops. In this work, via doping of La3+ into (Pb1-1.5xLax)(Zr0.5Sn0.43Ti0.07)O3 AFE ceramics, large EA and Eb due to respectively enhanced AFE phase stability and reduced electric conductivity, and slimmer hysteresis loops resulting from the appearance of the relaxor AFE state, are successfully obtained, and thus leading to great improvement of the Wre and η. The most superior energy storage properties are obtained in the 3 mol% La3+-doped (Pb1-1.5xLax)(Zr0.5Sn0.43Ti0.07)O3 AFE ceramic, which simultaneously exhibits at room temperature a large Wre of 4.2 J/cm3 and a high η of 78%, being respectively 2.9 and 1.56 times those of (Pb1-1.5xLax)(Zr0.5Sn0.43Ti0.07)O3 AFE ceramics with x = 0 (Wre = 1.45 J/cm3, η = 50%) and also being superior to many previously published results. Besides, both Wre and η change very little in the temperature range of 25–125 °C. The large Wre, high η, and their good temperature stability make the Pb0.955La0.03(Zr0.5Sn0.43Ti0.07)O3 AFE ceramic attractive for preparing high pulsed power capacitors useable in various conditions.