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The ZrB 2 –SiC composites have been commercially used at ultrahigh temperatures, but it often failed due to their poor toughness. In order to solve this problem, four types of Ta-containing additives (Ta, TaC, TaB 2 and TaSi 2) were used as the "third phase" to regulate the microstructure, so as to enhance the mechanical properties of hot-pressed ZrB 2 –20SiC-based ceramics (in vol. %). The incorporation of the additives generated a core–shell structure, which comprised of a ZrB 2 core and a (Zr, Ta)B 2 solid solution shell. The additives helped refine the ZrB 2 grains in addition to the metallic Ta and release the internal stress field generated by the thermal misfit. The interfacial structure was modified by the formation of the coherent core/shell interface and the semi-coherent interface of adjacent ZrB 2 grains and the semi-coherent ZrB 2 /(Zr, Ta)C interface in the TaC-additive composite. The addition of TaB 2 or TaC hardened the ZrB 2 –20SiC ceramics, whereas the addition of Ta or TaSi 2 reduced the hardness. The fracture toughness was enhanced by the formation of the Ta-containing phases. These phases reduced the stress intensity factor of the crack tip, which was proportional to the intrinsic residual stress. However, the crack-propagation mechanism would be changed by the incorporation of various Ta-containing additives. The decrease in the crack deflection, which was induced by the stronger interfacial bonding force and the significant consumption of SiC, resulted in relatively low toughness in the Ta- and TaC-included samples. The weaker interfacial bonding force in the TaB 2 - and TaSi 2 -included samples caused an increase in deflection and generated branching, which enhanced the toughness of the TaSi 2 -included composites to ∼4.72 MPa⸱m1/2. [ABSTRACT FROM AUTHOR]

A novel SiC–Si coating with a high amount of net-like distributed Si was fabricated on the graphite substrate by liquid silicon infiltration (LSI) method to improve the oxidation-resistant performance. The mass gain of this LSI coating after 300 h oxidation at 1873 K was only 3.018%, suggesting an excellent static antioxidant property at 1873 K. The detailed oxidation mechanism of this LSI coating was explored in this work. It was found that the high amount of Si with the net-like distribution in this LSI coating promoted the passivation growth of SiO 2 glass layer and prevented the SiO 2 glass from crystallizing into cristobalite. In addition, the Si in this coating retarded the active oxidation and enhanced the coating stability. In contrast, the infiltration (VSI) SiC–Si coating presented an apparent mass loss, and the pack cementation (PC) SiC coating showed the catastrophic failure. The oxidation mechanisms of these two coatings were also discussed against the backdrop of the LSI coating with high antioxidant performance. [ABSTRACT FROM AUTHOR]

A newly five-component equimolar high-entropy ceramic – (La 0.2 Eu 0.2 Gd 0.2 Y 0.2 Yb 0.2) 2 Zr 2 O 7 with a mixture phase of pyrochlore and fluorite structure was successfully synthesized. On this basis, a series of systematically designed and synthesized high or medium-entropy ceramics, accompanied by a large number of previous reports on multi-component rare earth zirconates, were summarized to jointly investigate the single-phase forming ability of high-entropy rare earth zirconates ceramics (HE-RE 2 Zr 2 O 7 for short) in terms of entropy value and cationic radius difference (δ). Subsequently, the forming process and mechanism of dual-phase solid solution were analyzed. The conclusions indicated that the single-phase forming ability was more determined by the cationic radius difference rather than the entropy value，and the critical value of δ distinguishing single-phase between dual-phase zone was around 5.2%. In addition, the formation of dual-phase solid solution was essentially driven by the size disorder resulting from rattler effect of cations with significant difference in radius. This work is the first report on the single-phase forming ability of HE-RE 2 Zr 2 O 7 and would pave new ways for predicting the formation of high-entropy phases. [ABSTRACT FROM AUTHOR]

Herein, a series of manganese-based NASICON structured Na 1+2 x Mn x Ti 2- x (PO 4) 3 (x = 1, 1.2, 1.4, denoted as NMTP, NM 1.2 T 0.8 P and NM 1.4 T 0.6 P) are obtained by sol-gel method and employed as cathodes for an aqueous sodium ion battery (ASIB). There is no obvious difference in structure among these samples, except for a small amount of impurity phase detected in NM 1.4 T 0.6 P. Three as-prepared samples exhibit impressive electrochemical performances, thereinto NM 1.2 T 0.8 P possesses the best electrochemical performance with the proper operating potential. NM 1.2 T 0.8 P delivers a discharge specific capacity of 68.2, 60.3, 52.2, 45.9 mAh g−1 at 1, 2, 5, 10 C, and still maintain 62.8 mAh g−1 when the current density returns to 1 C. Meanwhile, long-term cycling performance test shows that NM 1.2 T 0.8 P displays an initial discharge capacity of 46.4 mAh g−1 and still retains a reversible capacity of 39.1 mAh g−1 at 10 C rate after 300 cycles. Cyclic voltammetry demonstrates that both the diffusion and pseudocapacitance determine the sodium-ion (Na-ion) storage mechanism of NM 1.2 T 0.8 P and the pseudocapacitance dominates the charge/discharge processes. Besides, a cathode-limited full cell with NM 1.2 T 0.8 P cathode and NaTi 2 (PO 4) 3 anode was assembled and shows excellent long-term cycling performance with a capacity retention ratio of 81.9 % at 10 C after 200 cycles. This exploration of manganese-based NASICON structured Na 1+2 x Mn x Ti 2- x (PO 4) 3 provides an option for cathode materials of ASIB. • NASICON structured Na 1+2 x Mn x Ti 2- x (PO 4) 3 (x = 1, 1.2, 1.4) are obtained by reasonable structural designing. • These materials are firstly used as cathode in aqueous sodium ion battery and the results are promising. • NM 1.2 T 0.8 P (x = 1.2) shows excellent performance, and the charge storage is controlled by diffusion and pseudocapacitance. [ABSTRACT FROM AUTHOR]

The Na1+xAlxTi2−x(PO4)3/C (x = 0, 0.05, 0.10, 0.20) composites serving as anode for aqueous sodium ion battery are successfully synthesized through a facile sol–gel route. The results indicate that introduction of proper amount of aluminum has no obvious effect on the structure and morphology of NaTi2(PO4)3/C. Among the four synthesized samples, Na1.1Al0.1Ti1.9(PO4)3/C (NATP-0.10) exhibits the best electrochemical performance. NATP-0.10 delivers a discharge specific capacity of 115.8, 106.9, 98.4, and 89.1 mAh g−1 at 2, 5, 10, and 20 C rate, respectively, and still retains 114.7 mAh g−1 when the current density comes back to 2 C. Additionally, NATP-0.10 exhibits an initial discharge capacity of 102.9 mAh g−1 and still retains a reversible capacity of 90.1 mAh g−1 at 10 C rate after 200 cycles. Cyclic voltammetry and electrochemical impedance spectroscopy demonstrate the better electrochemical performance of NATP-0.10 is due to the faster sodium migration and enhanced electrochemical kinetics. Al doping Na1+xAlxTi2−x(PO4)3/C (x = 0, 0.05, 0.10, 0.20) composites were firstly used as anodes in aqueous SIBs. The electrochemical performance of NaTi2(PO4)3/C has been improved by introducing a proper amount of Al. [ABSTRACT FROM AUTHOR]