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排序方式: 共有1346条查询结果,搜索用时 15 毫秒
1.
Lalitha Kodumudi Venkataraman Tingting Zhu Monica Pinto Salazar Kathrin Hofmann Aamir Iqbal Waidha J. C. Jaud Pedro B. Groszewicz Jürgen Rödel 《Journal of the American Ceramic Society》2021,104(5):2201-2212
Na1/2Bi1/2TiO3-based materials have been earmarked for one of the first large-volume applications of lead-free piezoceramics in high-power ultrasonics. Zn2+-doping is demonstrated as a viable route to enhance the thermal depolarization temperature and electromechanically harden (1-y)Na1/2Bi1/2TiO3-yBaTiO3 (NBT100yBT) with a maximum achievable operating temperature of 150 °C and mechanical quality factor of 627 for 1 mole % Zn2+-doped NBT6BT. Although quenching from sintering temperatures has been recently touted to enhance TF-R, with quenching the doped compositions featuring an additional increase in TF-R by 17 °C, it exhibits negligible effect on the electromechanical properties. The effect is rationalized considering the missing influence on conductivity and therefore, negligible changes in the defect chemistry upon quenching. High-resolution diffraction indicates that Zn2+-doped samples favor the tetragonal phase with enhanced lattice distortion, further corroborated by 23Na Nuclear Magnetic Resonance investigations. 相似文献
2.
Qi Xiao Xinyao Dong Xiumei Yin Hong Wang Hua Zhong Mingming Xing Ying Tian Yao Fu Bin Dong Xixian Luo 《Journal of the American Ceramic Society》2021,104(3):1415-1423
Multicolor upconversion luminescence materials show significantly applications in materials science. In this paper, the novel Yb3+-sensitized Na3La(VO4)2 upconversion luminescence crystals are synthesized by the solid-state reaction method. Three primary colors upconversion luminescence are successfully achieved in Na3La(VO4)2:Yb3+,Tm3+, Na3La(VO4)2:Yb3+,Er3+, and Na3La(VO4)2:Yb3+,Ho3+ crystals excited by the single 980 nm LD. Multicolor upconversion luminescence can be obtained by simply adjusting the combination ratios of these three samples. Luminescence mechanisms of the Yb3+-sensitized system are discussed in detail. In the Na3La(VO4)2 host material, the Yb3+/Ho3+ codoped system exhibits unusual red upconversion luminescence based on the short decay time of Ho3+ ion 5I6 level, which provides the possibility of three primary color luminescence under 980 nm excitation. 相似文献
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4.
Liangtao Yang Liang-Yin Kuo Juan Miguel López del Amo Prasant Kumar Nayak Katherine A. Mazzio Sebastian Maletti Daria Mikhailova Lars Giebeler Payam Kaghazchi Teófilo Rojo Philipp Adelhelm 《Advanced functional materials》2021,31(38):2102939
A known strategy for improving the properties of layered oxide electrodes in sodium-ion batteries is the partial substitution of transition metals by Li. Herein, the role of Li as a defect and its impact on sodium storage in P2-Na0.67Mn0.6Ni0.2Li0.2O2 is discussed. In tandem with electrochemical studies, the electronic and atomic structure are studied using solid-state NMR, operando XRD, and density functional theory (DFT). For the as-synthesized material, Li is located in comparable amounts within the sodium and the transition metal oxide (TMO) layers. Desodiation leads to a redistribution of Li ions within the crystal lattice. During charging, Li ions from the Na layer first migrate to the TMO layer before reversing their course at low Na contents. There is little change in the lattice parameters during charging/discharging, indicating stabilization of the P2 structure. This leads to a solid-solution type storage mechanism (sloping voltage profile) and hence excellent cycle life with a capacity of 110 mAh g-1 after 100 cycles. In contrast, the Li-free compositions Na0.67Mn0.6Ni0.4O2 and Na0.67Mn0.8Ni0.2O2 show phase transitions and a stair-case voltage profile. The capacity is found to originate from mainly Ni3+/Ni4+ and O2-/O2-δ redox processes by DFT, although a small contribution from Mn4+/Mn5+ to the capacity cannot be excluded. 相似文献
5.
The Er3+ doped oxyfluorogermanate glasses, with a composition containing Na element, were synthesized by the conventional melting–quenching technique. When Na element was introduced into the composition of oxyfluorogermanate glass, the crystals behavior was investigated in details. Depending on the annealing procedure supplied, thermal annealing of precursor glasses in the system GeO2/BaF2/AlF3/Na2O/NaF/ZnO/GdF3/ErF3 led to the precipitation of different crystal phase nanocrystals. It was confirmed the nanocrystals in GC600 is orthorhombic NaBaAlF6 which led to enhance obviously in the UC luminescence of Er3+. However, the nanocrystals in G585 led to decrease in the UC luminescence, which indicated few Er ions enter into the lattice of this nanocrystal phase. The reason of the decrease in UC emission intensity of GC585 was analyzed. 相似文献
6.
In the present work we have studied the effect of Na on the properties of graded Cu(In1−xGax)Se2 (CIGS) layer. Graded CIGS structures were prepared by chemical spray pyrolysis at a substrate temperature of 350 °C on soda lime glass. Sodium chloride is used as a dopant along with metal (Cu/In/Ga) chlorides and n, n-dimethyl selenourea precursors. The addition of Na exhibited better crystallinity with chalcopyrite phase and an improvement in preferential orientation along the (112) plane. Energy dispersive analysis of X-rays (line/point mapping) revealed a graded nature of the film and percentage incorporation of Na (0.86 at%). Raman studies showed that the film without sodium doping consists of mixed phase of chalcopyrite and CuAu ordering. Influence of sodium showed a remarkable decrease in electrical resistivity (0.49–0.087 Ω cm) as well as an increase in carrier concentration (3.0×1018–2.5×1019 cm−3) compared to the un-doped films. As carrier concentration increased after sodium doping, the band gap shifted from 1.32 eV to 1.20 eV. Activation energies for un-doped and Na doped films from modified Arrhenius plot were calculated to be 0.49 eV and 0.20 eV, respectively. Extremely short carrier lifetimes in the CIGS thin films were measured by a novel, non-destructive, noncontact method (transmission modulated photoconductive decay). Minority carrier lifetimes of graded CIGS layers without and with external Na doping are found to be 3.0 and 5.6 ns, respectively. 相似文献
7.
《Journal of the European Ceramic Society》2019,39(16):5410-5422
An investigation of the two-component phase diagram of the CaNaPO4- CaKPO4system performed using various analysis techniques is reported. The continuous solid solution series of α-CaMPO4 existing above 700 °C undergoes eutectoid decomposition during cooling to β-CaMPO4-based solid solutions enriched with Na and K, and to an intermediate nonstoichiometric compound with an ideal composition of CaK0.6Na0.4PO4. All three compounds exhibit significant volumetric effects associated with first-order phase transitions, with positive volume changes under cooling for the intermediate compound. Increased K content in ceramics based on CaKyNa1-yPO4 compositions enhances the strength properties of those ceramics, including their fracture toughness, which is associated with increased density. Increased K content also has a smaller effect of inducing phase transformations accompanied by strong volume changes. 相似文献
8.
钠基膨润土胶质价测试方法的改进 总被引:1,自引:0,他引:1
以两种人工钠化膨润土为研究对象,探讨了文献胶质价测试方法的不合理性、取土量和MgO量这两个关键因素。实验结果表明:用常规100 mL量筒测胶质价时,取土量和MgO量影响较大,有必要针对具体试样做条件试验,最佳条件是1#钠土为取3.00 g土、0.2 g MgO,2#钠土为取5.00 g土、0.33 g MgO。 相似文献
9.
10.
目的 研究电解液中的Na2WO4含量对AZ31B镁合金微弧氧化膜层的形成过程、颜色、微观结构、耐蚀性能的影响。方法 通过添加不同含量的NH4VO3和Na2WO4的碱性铝酸盐电解液体系,在AZ31B镁合金表面制备黑色的微弧氧化膜层。采用SEM、EDS分析加入不同含量的Na2WO4后膜层表面的微观形貌及元素组成,采用XRD分析物相组成,通过电化学实验表征膜层的耐腐蚀性能。结果 随着Na2WO4含量的增加,微弧氧化过程中的起弧电压下降,膜层的致密性提高,厚度呈先增加后减小的趋势。当Na2WO4的质量浓度为0.5 g/L时,膜层的厚度最大,且此时膜层表面微孔分布均匀,色度最低,耐蚀性最好,自腐蚀电位为−0.138 V,自腐蚀电流密度为2.36×10−7 A/cm2,相较于基体降低了3个数量级。结论 增加Na2WO4含量会使微弧氧化成膜过程中的电弧发生变化,适当增加Na2WO4会提高膜层的厚度,降低膜层的CIE色度,使陶瓷膜层表面的微孔分布得更加均匀致密,从而提高膜层的耐蚀性能。当Na2WO4含量过高时,会使膜层的离子浓度升高,电阻增大,介电击穿电压上升,导致膜层表面被烧蚀,耐腐蚀性能降低。 相似文献