Kewei Wang,Baisheng Ma,Tao Li,Chunxiao Xie,Zhenzhong Sun,Dianguang Liu,Jinling Liu,Linan An
In this study, powder mixtures at atomic ratios suitable for formation of Sr(Ti 0.2 Y 0.2 Zr 0.2 Sn 0.2 Hf 0.2 )O 3-x were flash sintered at 1000 °C and 40 mA/mm 2 . X-ray diffraction and energy-dispersive spectroscopy analyses revealed the formation of single-phase oxides after sintering for 1 min. This rapid formation of single-phase oxide was attributed to flash sintering characteristics, which not only enhanced the diffusion rate, but also softened the lattice. Compared to conventional heat treatment sintering, the sintering time was shortened to 1 min from 10 h, while the sample temperature was reduced to 1314 from 1500 °C. Therefore, flash sintering is a promising technique for rapid synthesis of high-entropy oxides.
Yanfei Wang,Weiran Zhang,Jinping Du,Duan Li,Rongjun Liu
It is urgent to develop thermal barrier coating (TBC) topcoat materials with ultra-low thermal conductivities for next-generation gas turbine engines. A novel pyrochlore-based single-phased ceramic, tuned by codoping of lanthanum zirconate, (La 1-x Y x ) 2 (Zr 1-y Ce y ) 2 O 7 , has been synthesized from the solid state reaction method. The thermal conductivity of (La 1-x Y x ) 2 (Zr 1-y Ce y ) 2 O 7 not only exhibits a temperature-independent trend but also reaches as low as 0.93 W·m −1 ·K −1 , a value that is lowest of fully dense crystalline solids in open literature, attributing to the following two combined effects. The first is the strong scattering of phonons by small-sized Y 3+ cations occupying the oversized atomic cages formed by the distinctive pyrochlore structure. The second is the lattice softening effects arising from larger-sized Ce 4+ substituting Zr 4+ cations. The above two effects act in concert and thus form a glasslike and ultra-low thermal conductivity of (La 1-x Y x ) 2 (Zr 1-y Ce y ) 2 O 7 solid solutions, which is ideal for next-generation TBC topcoat applications.
The high theoretical capacity of Sb-based intermetallic alloys makes them attractive potential anode materials for sodium-ion batteries (SIBs) with high energy density . However, their cycling stability is greatly restricted by the huge volumetric variations resulted from the intrinsic (de-)alloying mechanism. Herein, we demonstrate a unique lattice softening mechanism, which enables highly reversible sodium storage and stable cycling of the as-prepared Bi–Sb alloy/carbon nanofibers electrodes. Theoretical analyses show that the elastic modulus of Bi–Sb alloys is reduced whereas the toughness is enhanced by tuning the lattice chemistry of rhombohedral Bi–Sb alloys, which is of great importance in relieving the concentrated stress during the continuous (de-)sodiation processes. In-situ characterization and electrochemical evaluations demonstrate that the electrodes made of BiSb 3 /C nanofibers exhibit high anti-pulverization capability upon Na-cycling and extraordinary long-life cyclability. Specifically, a highly reversible capacity of 233.2 mAh g −1 at 2 A g −1 is achieved over 2500 cycles. Moreover, a full cell assembled with the pre-sodiated BiSb 3 /C anode and a Na 3 V 2 (PO 4 ) 3 /C cathode delivers a high reversible capacity of 333.2 mAh g −1 at 0.2 A g −1 over 200 cycles. This present work provides further understandings and new solution for developing high-performance alloying-based anodes for SIBs.
The development of a solid electrolyte with superb Li+ conductivity is the key to enabling safe and high-performance all-solid lithium ion batteries which are free of the safety issues associated with flammable organic liquid electrolyte. Systematic experimental work has been carried out as a follow up to our recent theoretical prediction that superb ionic conductivity could be achieved through the tuning of the lattice chemistry in the cubic argyrodite Li6PS5Cl. Remarkable enhancement of the ionic conductivity has been achieved through the combined effect of excess Li and substitution of S with Te. This leads to an alloy, Li6.25PTe0.125S5.125Cl0.75, having the superb Li+ conductivity of 4.5 mS cm−1 at 25 °C, together with a low activation energy of 0.16 eV to safeguard adequate ionic conductivity at low temperature. This current work conclusively affirms the theoretical outcome that the superb ionic conductivity is attributed to weakened bonding, an enlarged unit cell, and a softened lattice, making it easier for the long-distance diffusion of Li+. In addition, this new class of solid electrolyte based on cubic chalcogenide is electrochemically compatible with the Li anode over a large potential window up to 7 V, which is highly desirable for high performance solid lithium ion batteries.
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