Qiaoji Zheng

Piezoelectric and ferroelectric properties of (Bi0.94−xLaxNa0.94)0.5Ba0.06TiO3 lead-free ceramics

Lead-free piezoelectric ceramics (Bi0.94−x LaxNa0.94)0.5Ba0.06TiO3 have been fabricated by an ordinary sintering technique, and their piezoelectric and ferroelectric properties have been studied. The results of x-ray diffraction reveal that La3+ and Ba2+ diffuse into the Bi0.5Na0.5TiO3 lattices to form a new solid solution with a pure perovskite structure. After the partial substitution of La3+ for Bi3+ in the (Bi0.94−x Lax Na0.94)0.5Ba0.06TiO3 ceramics (x = 0–0.04), the ceramics exhibit a lower coercive field Ec and a larger remanent polarization Pr. Because of the large Pr and low Ec, the ceramics with x = 0.02–0.04 exhibit optimum piezoelectric properties: d33 = 181–196 pC N−1 and kP = 33.2–36.3%. The depolarization temperature Td decreases with increasing x (x = 0 − 0.04). At the high La3+ level (x = 0.06–0.12), the ceramics exhibit weak ferroelectricity and thus possess very poor piezoelectricity, and the low dielectric anomaly at Td disappears. In addition, the ceramics exhibit a relaxor characteristic, which probably results from the cation disordering in the 12-fold coordination sites. The temperature dependences of the ferroelectric and dielectric properties suggest that the ceramics with x = 0–0.04 may contain both polar and non-polar regions at temperatures above Td, while for the ceramics with x = 0.06–12, the polar and non-polar regions coexist at room temperature.

Critical roles of Mn-ions in enhancing the insulation, piezoelectricity and multiferroicity of BiFeO3-based lead-free high temperature ceramics

A lead-free multiferroic ceramic of BiFe0.96Sc0.04O3–BaTiO3 is a type of ABO3 perovskite structure, belonging to the R3c space group, but exhibiting poor insulation and weak multiferroicity. In this work, the critical roles of Mn-ions in tailoring the electrical and magnetic properties of BiFeO3-based materials are revealed: the introduction of MnO2 into BiFe0.96Sc0.04O3–BaTiO3 induces a dramatic improvement in insulation, piezoelectricity and multiferroicity. New compositions of BiFe0.96Sc0.04O3–BaTiO3 + x mol% MnO2 were synthesized by a conventional solid-state reaction method. All the ceramics possess a perovskite structure, and a morphotropic phase boundary (MPB) of rhombohedral and monoclinic phases is formed at x = 0.5–1.0. The formation of and is noticeably suppressed and the resistivity of the ceramics is increased by ∼100 times after the addition of 0.5–1.0 mol% MnO2, which make the ceramic polarizable and thus give strong ferroelectricity and considerable piezoelectricity. The ceramics with the MPB composition exhibit high electrical insulation (R = 1.2–1.7 × 1010 Ω cm), good piezoelectricity (d33 = 123–143 pC N−1, kp = 0.34–0.35), strong ferroelectricity (Pr = 13.1–17.6 μC cm−2), high Curie temperature (590–596 °C) and excellent temperature stability of piezoelectric and ferroelectric properties. These improvements are greatly associated with the contribution of Mn ions in the ceramics. Surprisingly, sharply enhanced ferromagnetism with Mr = 0.4946 emu g−1 and Ms = 1.0298 emu g−1 is obtained in the ceramic with x = 7.0, almost one thousand times larger than that of an un-doped ceramic. The origin of unusual ferromagnetism is associated with significant changes in magnetic ordering caused by Mn doping. The high magnetoelectric effect (α33 = 429.6 mV cm−1 Oe−1) is obtained after the addition of 2.0 mol% Mn ions. Our study suggests that the present ceramics may have potential applications in advanced memory devices as promising lead-free high temperature piezoelectric and multiferroic materials.

Enhanced ferroelectricity, piezoelectricity, and ferromagnetism in Nd-modified BiFeO3-BaTiO3 lead-free ceramics

Lead-free multiferroic ceramics of 0.75Bi1−xNdxFeO3 − 0.25BaTiO3 + 1 mol. % MnO2 were prepared by a conventional ceramic technique and their structure, piezoelectricity, and multiferroicity were studied. The ceramics sintered at 890–990 °C possess a pure perovskite structure. A morphotropic phase boundary of rhombohedral and monoclinic phases is formed at x = 0.05. A small amount of Nd improves the ferroelectric and piezoelectric properties of the ceramics. The ferroelectric-paraelectric phase transition becomes gradually diffusive with x increasing. After the addition of Nd, the ferromagnetism of the ceramics is greatly enhanced by ∼320%. The increase in sintering temperature improves significantly the ferroelectric, piezoelectric, and ferromagnetic properties of the ceramics. The ceramics with x = 0.05 sintered at 950–990 °C possess improved ferroelectricity, piezoelectricity, magnetism and insulation with Pr of 16.5–17.5 μC/cm2, d33 of 113–121 pC/N, Mr of 0.127–0.138 emu/g, R of ∼5 × 109 Ω·cm and high ...

A high-efficiency N/P co-doped graphene/CNT@porous carbon hybrid matrix as a cathode host for high performance lithium–sulfur batteries

Heteroatom-doped carbon hybrids containing sp2-hybridized and sp3-hybridized nanocarbons have attracted immense interest as sulfur hosts due to their unique 3D conductive networks and synergistic effect of physical absorption and chemical interaction on suppressing the dissolution of polysulfides. However, the reported carbon hybrids always require a tedious fabrication process, including multistep chemical vapor deposition and a thermally stable catalyst. Therefore, it is highly desirable to exploit a simple, renewable, and scalable strategy to fabricate 3D heteroatom-doped carbon hybrids. Herein, a N, P-co-doped 3D carbon hybrid was successfully fabricated via a one-pot pyrolysis process. Due to the rapid Li+/e− transport among the 3D interconnected porous frameworks and effectively suppressed polysulfide dissolution by physical confinement and chemical interaction, the assembled Li–S batteries exhibit excellent electrochemical performance. The as-obtained cell delivers an ultrahigh initial discharge capacity of 1446 mA h g−1 at 0.1C as well as an excellent rate capability of 921 mA h g−1 at 1C. Additionally, a reversible and stable discharge capacity of 795 mA h g−1 is maintained after 400 cycles at 1C, corresponding to an extremely low capacity decay of 0.034% per cycle. Such a design strategy is eco-friendly and generally applicable to combine the sp2 nanocarbon with sp3 amorphous carbon, which is crucial to construct 3D interconnected hierarchical porous carbons for advanced energy storage for applications in various fields, such as lithium batteries, catalysis and hydrogen storage.

Regulated morphology/phase structure and enhanced fluorescence in YF3:Eu3+,Bi3+via a facile method

A simple and facile hydrothermal method has been developed to enhance the fluorescence performance of YF3:xEu3+,y%Bi3+ (x = 0–0.2, y = 0–1.5) by optimizing the concentration of Eu3+ and Bi3+ and regulating the morphology/phase structure by controlling the amount of HNO3. The evolutionary mechanisms of the micro-topography and microstructure of the samples have been proposed, and the fluorescence and decay properties of the samples have been investigated. It was found that the fluorescence intensity of the sample has been greatly enhanced after addition of an opportune amount of Bi3+. The optimum concentrations of Eu3+ and Bi3+ for fluorescence are x = 0.125 and y = 0.5%, respectively. The significant enhancement in fluorescence performance could be obtained in the sample with the desired morphology at the optimum volume of HNO3 (VHNO3 = 11 mL).

Enhanced ferroelectricity/piezoelectricity, bright blue/yellow emission and excellent thermal stability in Ca1−x(LiDy)x/2Bi4Ti4O15 lead-free multifunctional ceramics

A new lead-free solid solution of Ca1−x(LiDy)x/2Bi4Ti4O15 has been developed and prepared by a conventional solid state reaction method. The partial substitution of (Li0.5Dy0.5)2+ for Ca2+ ions in CaBi4Ti4O15 leads to great multi-improvement in the ferroelectricity/piezoelectricity, luminescence and thermal stability of the materials. All the ceramics possess a bismuth-layer structure; and the crystal structure of the ceramics is transformed from four layer bismuth-layer structure to a three layer structure with x increasing. For the ceramic with x = 0.2, high resistivity (R = 3.0 × 1011 Ω cm), good piezoelectricity (d33 = 10.5 pC N−1), strong ferroelectricity (Pr = 9.92 μC cm−2) and improved luminescence are simultaneously obtained. These enhancements in multifunctional properties are greatly attributed to the contribution of (Li0.5Dy0.5)2+ in the ceramics. Under the excitation of 451 nm light, the (LiDy)2+-modified ceramics exhibit bright blue and yellow emission peaks centered at 484 nm and 574 nm, corresponding to the transition of the 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 levels of Dy3+ ions, respectively. Interestingly, excellent temperature stability of the ferroelectricity/piezoelectricity and luminescence is also observed in the ceramic with x = 0.2. These results show that Ca1−x(LiDy)x/2Bi4Ti4O15 multifunctional ceramics may have promising potential in high temperature multifunctional devices.

Enhanced piezoelectricity and photoluminescence in Dy-doped Ba0.85Ca0.15Ti0.9Zr0.1O3 lead-free multifunctional ceramics

Lead-free multifunctional ceramics of Ba0.85Ca0.15Ti0.9Zr0.1O3-x mol% Dy have been prepared by an ordinary sintering method and the effects of Dy2O3 doping on structure, piezoelectric, ferroelectric and photoluminescent properties of the ceramics have been studied. The ceramics possess a single phase perovskite structure. The grain growth of the ceramics is prohibited and the ferroelectric–paraelectric phase transition at TC becomes more diffusive after the addition of Dy2O3. Dy2O3 doping improves the piezoelectricity of the ceramics and the optimal piezoelectric properties d33 = 335 pC/N is obtained at x = 0.5. The addition of 2 mol% Dy enhances the photoluminescent properties of the ceramics and strong emissions at ∼ 478 nm and ∼ 575 nm are observed. Our study shows that the ceramics with low Dy2O3 levels exhibit simultaneously the strong piezoelectricity, ferroelectricity and photoluminescence and may have a potential application in mechano-electro-optic integration and coupling device.

Rational design of a multidimensional N-doped porous carbon/MoS2/CNT nano-architecture hybrid for high performance lithium–sulfur batteries

Exploring a stable and high-efficiency sulfur cathode with strong polarity and a robust porous conductive framework is a critical challenge to develop advanced lithium–sulfur (Li–S) batteries. Herein, a multidimensional N-doped porous carbon/MoS2/CNT (FSC/MoS2/CNT) nano-architecture hybrid is rationally designed and successfully fabricated by the facile pyrolysis and hydrothermal processes. For the nano-architecture composite, the porous carbon embedded with electroconductive acid-treated CNTs effectively enhances the flexibility and constructs a conductive network for rapid ion/electron transfer; specifically, a synergistic action of polar MoS2 and electronegative doped N atoms significantly strengthens the chemical affinity with polysulfides; furthermore, MoS2 exhibits a strong catalytic effect that can improve the redox kinetics of polysulfides. On account of the merits mentioned above, the as-built N-doped porous carbon/MoS2/CNTs@S (FSC/MoS2/CNTs@S) composite, utilized as the Li–S battery cathode, delivers a high discharge capacity of 1313.4 mA h g−1 at 0.1C, glorious rate performance with 671.6 mA h g−1 at 2.0C and remarkable cycling stability with a capacity fading rate of 0.059% per cycle for 500 cycles at 1.0C. This work provides a novel and simple strategy to design a CNT decorated polar and conductive hybrid network of doped porous carbon/transition metal sulfide for application in excellent performance Li–S batteries and numerous energy storage fields.

Enhanced cycling stability and rate capability of Bi2O3-coated Li1.2Mn0.54Ni0.13Co0.13O2 cathode materials for lithium-ion batteries

Li-rich layered oxide of Bi2O3-coated Li1.2Mn0.54Ni0.13Co0.13O2 was fabricated via a combined method of sol–gel and wet chemical coating processes. The crystal structure of Li1.2Mn0.54Ni0.13Co0.13O2 has no obvious change after the coating of 2 wt% Bi2O3. Bi2O3 is homogenously coated on the surface of Li1.2Mn0.54Ni0.13Co0.13O2 particles. The Bi2O3-coated Li1.2Mn0.54Ni0.13Co0.13O2 electrode presents an enhanced cycling stability, better rate performance and lower charge transfer resistance. After the coating of 2 wt% Bi2O3, the initial coulombic efficiency of the material has been improved to 76.9% compared to 72.6% for the bare Li1.2Mn0.54Ni0.13Co0.13O2. After 100 cycles at 0.1C, the Bi2O3-coated Li1.2Mn0.54Ni0.13Co0.13O2 electrode retains a discharge capacity of 182.9 mA h g−1 with capacity retention of 73.5%, which are much higher than those of Li1.2Mn0.54Ni0.13Co0.13O2 (146.9 mA h g−1 and 58.8%). In addition, the Bi2O3-coated Li1.2Mn0.54Ni0.13Co0.13O2 electrode exhibits better rate capability with discharge capacities of 155.8, 124.8 and 89.2 mA h g−1 at 1, 2 and 5C, respectively, superior to that of Li1.2Mn0.54Ni0.13Co0.13O2. The enhanced cycling stability and rate capability should be ascribed to the existence of Bi2O3 on the surface of the active material, which can efficiently restrain the side reactions between the electrode and electrolyte, stabilize the structure of Li1.2Mn0.54Ni0.13Co0.13O2 and improve the lithium ion diffusion.

Effects of Nb doping on the microstructure, ferroelectric and piezoelectric properties of 0.7BiFeO3-0.3BaTiO3 lead-free ceramics

Donor-doped lead-free Bi0.7Ba0.3(Fe0.7Ti0.3)1−xNb0.66xO3 + 1 mol% MnO2 ceramics were prepared by a conventional oxide-mixed method and the effects of Nb-doping on microstructure, piezoelectric and ferroelectric properties of the ceramics were investigated. All the ceramics exhibit a pure perovskite structure with rhombohedral symmetry. The grain growth of the ceramics is inhibited after the addition of Nb doping. High electric insulation (R = 109–1010 Ω⋅cm) and the poor piezoelectric performance and weak ferroelectricity are observed after the addition of Nb2O5 in the ceramics. Different from the donor effect of Pb-based perovskite ceramics, the introduction of Nb into 0.7BiFeO3–0.3BaTiO3 degrades the piezoelectricity and ferroelectricity of the ceramics. The Bi0.7Ba0.3(Fe0.7Ti0.3)1−xNb0.66xO3 + 1 mol% MnO2 ceramic with x = 0 exhibits the optimum piezoelectric properties with d33 = 133 pN C−1 and kp = 0.29 and high Curie temperature (TC = 603∘C).