[en] Highlights: • A novel salt of LiBSO_4F_2 is used as an functional electrolyte additive. • Electrolyte with LiBSO_4F_2 has high stability against oxidation decomposition (∼5.6 V). • LiBSO_4F_2 additive could decrease the interfacial impedance of LiNi_0_._5Mn_1_._5O_4/Li cells. • LiBSO_4F_2 additive could improve electrochemical performance of LiNi_0_._5Mn_1_._5O_4/Li cells. - Abstract: To seek a promising candidate for 5 V electrolytes, fluorine-free lithium bis(oxalato) borat (LiBOB) is chosen as the lithium salt, and lithium difluoro(sulfato) borate (LiBSO_4F_2) is investigated as an additive for the stabilization of a high-voltage LiNi_0_._5Mn_1_._5O_4 cathode. Cyclic voltammetry test, AC impedance measurement and scanning electron microscopy (SEM) analysis are used to examine the electrochemical stability and the compatibility between electrolytes and LiNi_0_._5Mn_1_._5O_4 cathode. It is found that the addition of 0.1 M LiBF_2SO_4 to 0.7 M LiBOB-based electrolyte could significantly decrease the interfacial impedance of LiNi_0_._5Mn_1_._5O_4/Li cells, due to the fact that LiBSO_4F_2 is involved in the formation of protective film on cathode surface, as well as the prior oxidation reactions of LiBOB. Moreover, LiBSO_4F_2 additive could obviously improve both of the capacity retention and the rate performance of lithium-ion cells. These results demonstrate that using blend salts can combine the advantages of LiBOB and LiBSO_4F_2 to maximize the electrochemical performances of lithium-ion cells

[en] Highlights: • The crystal structure of Ca_xZn_1−xSn_0.08Ti_1.92Nb₂O₁₀ ceramics were analyzed. • The quantitative determination of Ca_xZn_1−xSn_0.08Ti_1.92Nb₂O₁₀ ceramics were analyzed. • The typical values of ε = 53.09, Qf = 48,000 GHz, τ_f = 21.20 ppm/°C were obtained. -- Abstract: The quantitative determination and the crystal structure of Ca_xZn_1−xSn_0.08Ti_1.92Nb₂O₁₀ ceramics were analyzed by X-ray diffraction, the microwave dielectric properties were investigated. The results showed that the Ca_xZn_1−xSn_0.08Ti_1.92Nb₂O₁₀ ceramics contained three main phases: ZnTiNb₂O₈ phase, Zn_0.15Nb_0.30Ti_0.55O₂ phase and Unknown Columbite-type phase. With the increase of Ca content, the weight fraction of secondary phase Zn_0.15Nb_0.30Ti_0.55O₂ and Unknown Columbite-type phase increased. For ZnTiNb₂O₈, with the substitution of Ca²⁺ for Zn²⁺, the bond valence of Ti-site increased. The variation of distortion of oxygen octahedral was irregular. For Zn_0.15Nb_0.30Ti_0.55O₂, the distortion of oxygen octahedral and the bond valence of Ti-site increased with substitution of Ca²⁺. The increase of Ti-site bond valence led to a harder rattling of Ti cations of the specimens. As a result, the dielectric constant (ε) and the quality factor value (Qf) decreased, the temperature coefficient of resonant frequency (τ_f) moved to the positive direction. The typical values of ε = 53.09, Qf = 48,000 GHz, τ_f = 21.20 ppm/°C were obtained for Ca_xZn_1−xSn_0.08Ti_1.92Nb₂O₁₀ (x = 0.02) specimens sintered at 1120 °C for 6 h. The relative low sintering temperature and high dielectric properties in microwave range make these ceramics promising for application in multilayer ceramic capacitors

[en] Highlights: • BaCu(B₂O₅) is added to the multi-ions doped SrTiO₃ ceramics as sintering aid. • The sintering temperature is decreased from 1300 °C to 1075 °C. • The incorporation of Ba²⁺ into the matrix increases the dielectric constant. • The breakdown strength increases due to the decrease of grain size and porosity. • The dissolution of BCB contributes to the improvement of dielectric properties. -- Abstract: BaCu(B₂O₅) (BCB) was used as sintering aids to lower the sintering temperature of multi-ions doped SrTiO₃ ceramics effectively from 1300 °C to 1075 °C by conventional solid state method. The effect of BCB content on crystalline structures, microstructures and properties of the ceramics was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and dielectric measurements, respectively. The addition of BCB enhanced the breakdown strength (BDS) while did not sacrifice the dielectric constant. The enhancement of BDS should be due to the modification of microstructures, i.e., smaller and more homogeneous grain sizes after BCB addition. The dielectric constant of BCB-doped ceramics maintained a stable value with 1.0 mol% BCB, which was dominated by the combination of two opposite effects caused by the presence of second phases and the incorporation of Cu²⁺ and Ba²⁺, while further increase was owing to the increase of dissolved Ba²⁺ ions when the content of BCB is more than 2.0 mol%. The multi-ions doped SrTiO₃ ceramics with 1.0 mol% BCB addition showed optimal dielectric properties as follows: dielectric constant of 311.37, average breakdown strength of 28.78 kV/mm, discharged energy density of 1.05 J/cm³ and energy efficiency of 98.83%

[en] Highlights: • LiBF_2SO_4 was investigated as a novel salt for advanced lithium-ion batteries. • LiBF_2SO_4-EC/DEC shows excellent film-forming characteristic on the surface of LiMn_2O_4. • LiBF_2SO_4-based electrolyte has good compatibility with LiMn_2O_4 cathode. - Abstract: Lithium difluoro(sulfato)borate (LiBF_2SO_4) is investigated as a lithium salt for non-aqueous electrolytes for LiMn_2O_4 cathode in lithium-ion batteries. Inductively coupled plasma-atomic emission spectrometry analysis is used to analyze the Mn dissolution. Scanning electron microscopy and AC impedance measurements analysis are used to analyze the formation of the surface film on the surface of LiMn_2O_4 cathode. These results demonstrate that LiBF_2SO_4-based electrolyte favourably facilitates the formation of an effective and conductive interface film on the cathode surface to improve the stabilization of cathode/electrolyte interface. Besides, LiMn_2O_4 cells using LiBF_2SO_4-based electrolyte exerts several advantages, such as stable cycling performance, low cell impedance, low polarization resistance, and good rate performance. It suggests that LiBF_2SO_4-based electrolyte has good compatibility with LiMn_2O_4 cathode, and LiBF_2SO_4 would be a very promising lithium salt for LiMn_2O_4 cathode in lithium-ion batteries

[en] Fracture failure analysis on ultra supercritical turbine bolts was carried out by means of chemical composition analysis, mechenical properties testing, metallographic examination and fracture analysis. The results show that the main reason of the bolts fracture is high temperature stress-rupture, with the fracture morphology being intergranular cracking character. The main fracture is perpendicular to the axial direction of bolt, which indicates that the tensile working stress result in the crack. In addition, another kind of cracks which is 45ºof the axis has been found on the bolt. It indicates that there must be some abnormal torsion stress on the bolt which most possibly be caused during assembling process. (paper)

[en] Highlights: • Colossal permittivity (66886) is achieved in this system by doping Nb₂O₅ and sintering in reducing atmosphere synchronously. • The self-compensation mechanism is revealed in BaTiO₃ ceramics according to different content of Nb₂O₅. • The internal polarization mode is adjusted, and the mechanism of different polarization is revealed. -- Abstract: Based on adjusting the relationship between polarization and charge carriers, barium titanate (BaTiO₃) ceramics with colossal permittivity and high insulation resistivity are prepared by solid-state reaction approach. Modified by reducing atmosphere (0.1%H₂/N₂) and donor-ions doping, different polarization modes are discussed via treatment with impedance analysis and dielectric data, then the relationship between dielectric properties and charge carriers is established. It is illustrated that the interfacial polarization and hopping polarization can be adjusted along with different charge compensation modes by changing Nb⁵⁺ content from 0.5 mol% to 3 mol%, corresponding to colossal permittivity and insulation resistivity, respectively. Thus, the approach provides an adjustable mechanism for balancing the colossal permittivity and insulation resistivity in BaTiO₃ ceramics. The colossal permittivity can be achieved by controlling oxygen vacancies, and the distribution of oxygen vacancies is further adjusted by the donor-ions. Meanwhile, the self-compensation is found in the grains to improve the grain resistance. On this basis, single-layer microchip capacitors of BaTiO₃-based ceramics are available in the future.

[en] NiO thin films with different annealing temperature and films thickness were fabricated by magnetron sputtering on the Pt/TiO_x/SiO₂/Si substrates. The XRD results show the crystallinity of films can be improved with the annealing temperature and films thickness increased. While the preferential orientation is affected by annealing temperature and films thickness. The SEM results show that the average size of the needle like grains shape increases gradually from 42.4 nm to 72.5 nm and the grains of films are seen to be more uniform, with a smoother and finer morphology with film thickness increasing. XPS measurements show that two valence states of Ni²⁺ and Ni³⁺ exist in NiO films with the Ni²⁺/ Ni³⁺ ratio 1.01. However, the Ni³⁺ refers to the structure that contains Ni²⁺ ions with holes and not to Ni₂O₃ phase as observed from the XRD results and the O1s XPS spectra, making the grains conductive due to plenty of holes. It results the grains have a key contribution to dielectric behavior. The frequency domain spectroscopy shows the films thickness and annealing temperature have a significance influence on the dielectric constant and dielectric loss tangent. And the preferential orientation of NiO films play a non-negligible impact on the dielectric performance due to the polarized NiO (111) plane.

[en] Microwave ceramic with ultra-high Q value is one of the most significant classes of material to realize the miniaturization and integration of microwave devices. In this paper, to improve the microwave dielectric properties of ceramics, MgTiO₃-x wt.% MgF₂ (x = 0, 3, 4, 5, and 6) microwave ceramics with high-quality factor were synthesized by solid-state reaction method. The effects of MgF₂ addition on the phase composition, sintering behavior, and microwave dielectric properties of MgTiO₃ were investigated. In comparison to pure MgTiO₃, our study demonstrates that the Q × f values can be dramatically enhanced with the doping of MgF₂. After being sintered at 1300 °C for 4 h, the MgTiO₃-3 wt.% MgF₂ showed the best microwave dielectric properties of ε_r ∼18.09, Q × f ∼262,900 GHz (at 8.98 GHz) and τ_f ∼ −41.5 ppm/°C. The outstanding performance of MgF₂ doped MgTiO₃ ceramics provides a solid foundation for widespread applications of microwave dielectric substrates, resonators, filters and patch antennas in modern wireless communication equipment.

[en] LiZn_1-xM_xNbO₄ (M = Co, Ni) (x = 0–0.06) systems were fabricated by a facile solid-state reaction method. Structure and property relationships of spinel structured LiZn_1-xM_xNbO₄ were investigated systematically. Appropriate amount of Co²⁺ and Ni²⁺ greatly improved the dielectric loss of LiZnNbO₄ ceramics. While, the dielectric loss deteriorated seriously when the doping content exceeded x = 0.02. The origin of dielectric loss in LiZn_1-xM_xNbO₄ ceramics was investigated systematically. Moreover, the theoretical dielectric constant and linear expansion coefficient were calculated on the bases of the crystallographic parameters from XRD refinement. The temperature coefficient of resonant frequency calculated by the P-V theory agreed well with the test values. Due to the small doping content, the change in chemical bonds was negligible. Density became the major factor determining the variation of dielectric constant in LiZnNbO₄ ceramics. At last, excellent microwave dielectric properties were obtained: Ts = 1010 °C, ε_r = 15.25, Qf = 107,000 GHz, τ_f = −63.3 ppm/°C for LiZn_0.98Co_0.02NbO₄ and Ts = 995 °C, ε_r = 14.85, Qf = 104,000 GHz, τ_f = −61.7 ppm/°C for LiZn_0.98Ni_0.02NbO₄.

[en] The (La_1/2Ta_1/2)_xTi_1-xO₂ and (Er_1/2Ta_1/2)_xTi_1-xO₂ ceramics with x = 0.01 and 0.03 were synthesized by a conventional solid-state reaction. The analysis of EDS mapping, ac conductivity spectra, impedance analysis, XPS, and DC bias indicate that electrons-pinned defect-dipole (EPPD) polarization plays the main role in both the (La_1/2Ta_1/2)_0.01Ti_0.99O₂ and (Er_1/2Ta_1/2)_0.01Ti_0.99O₂ ceramics, while the interfacial polarization and hopping polarization are respectively highlighted by the (La_1/2Ta_1/2)_0.03Ti_0.97O₂ and (Er_1/2Ta_1/2)_0.03Ti_0.97O₂ ceramics. Besides, the dielectric responses reveals that the interfacial polarization and hopping polarization are much slower than EPDD polarization and lead to poor frequency-, temperature-stability and higher dielectric loss (tanδ). Then the conclusion can be drawn that the outstanding dielectric properties can be achieved only the EPDD polarization takes the absolute dominant position, and excellent properties are obtained in (Er_1/2Ta_1/2) _0.01Ti_0.99O₂ ceramic with ultra-low loss of tanδ≈0.0095 (@1 kHz) and excellent frequency, temperature and DC bias stability.