Luminescence Properties and Site Substitution of Eu^（3＋）and Bi^（3＋） in Me_2Y_8（SiO_4）_6O_2

Under UV excitation, Eu￣(3+) and Bi￣(3+) ions show red (￣5D_0-￣7F_2) and blue emissions (￣3P_1-￣1S_0) in Me_2Y_8(SiO_4)_6O_2, respectively. The luminescence properties of Eu￣(3+) depend strongly on Me￣(2+) and excitation wavelengths. For all Me￣(2+), Eu￣(3+) ions enter 4f and 6h sites simultaneously according to the fluorescence Raman spectra excited by Ar￣+ 476.5 nm laser. Different Me￣(2+) yields different Bi￣(3+) emission intensity and Stokes shift. Bi￣(3+) ions enter 4f and 6h sites mainly for Me=Ca, Zn and for Me=Mg, Sr,respectively.

Enhanced Thermoelectric Performance of Non-equilibrium Synthesized Fe0.4Co3.6Sb12-xGex Skutterudites via Randomly Distributed Multi-scaled Impurity Dots

The p-type Ge doped Fe0.4Co3.6Sb12-xGex skutterudites with multi-scaled impurity dots（500 nm-2 mm） were successfully prepared by using melt-quenching（MQ） and subsequent spark plasma sintering（SPS） technique. Compared with traditional method, the new technology significantly shortened the processing time from several days to less than 24 hours. The phase of impurity dots was demonstrated to be CoSb through analysis of X-ray diffraction（XRD） and energy-dispersive spectrum（EDS）. Impurity dots were induced by Ge substitution of Sb in the non-equilibrium synthesized process. Due to the abandonment of the long reaction of annealing crystallization, a few of Ge atoms would fail to substitute Sb site of skutterudite in this non-equilibrium synthesized process, leading to that the multi-scaled impurity dots randomly distributed in the matrix of skutterudite Fe0.4Co3.6Sb12-xGex. The combination of multi-scaled impurity dots scattering long wavelength heat-carrying phonons and the point defect scattering short and middle wavelength heat-carrying phonons dramatically made the 22.2% reduction of lattice thermal conductivity. As a result, compared with unsubstituted sample of Fe0.4Co3.6Sb12, the maximum ZT value was increased by 30.5%. Thus, the two marked features of this new synthesis process, the shortened preparation time and the enhanced thermoelectric performance, would make a promising commercial application in the future.

Metal-organic framework-derived Fe/Cu-substituted Co nanoparticles embedded in CNTs-grafted carbon polyhedron for Zn-air batteries

Metal-organic frameworks(MOFs)and MOF-derived materials have attracted great attention as alternatives to noble-metal based electrocatalysts owing to their intriguing structure properties,especially for high efficiency and stable oxygen reduction reaction(ORR).Herein,we employed a one-pot reaction to make a multimetal(Fe,Co,Cu,and Zn)mixed zeolitic imidazolate framework(MM-ZIF)via adopting a simple in situ redox reaction.Further pyrolysis of the target MM-ZIF,a highly porous carbon polyhedron(FC-C@NC)grafted with abundant carbon nanotubes was obtained,in which ultrasmall Co nanoparticles with partial lattice sites substituted by Fe and Cu were embedded.The obtained FC-C@NC possessed large surface area,highly porous structure,widely-spread metal active sites,and conductive carbon frameworks,contributing to outstanding ORR activity and long-term stability.It displayed superior tolerance to methanol crossover and exceeded the commercial Pt/C catalyst and most previously reported non-noble-metal catalysts.Impressively,the as-produced FC-C@NC-based zinc-air battery afforded an open-circuit potential of 1.466 V,a large specific capacity of 659.5 mAh/g,and a high gravimetric energy density of 784.3 Wh/kgZn,significantly outperforming the Pt/C-based cathode.

Phase evolution and mechanical properties of novel nanocrystalline Y_(2)(TiZrHfMoV)_(2)O_(7) high entropy pyrochlore

High entropy pyrochlores(HEP)are potential candidates as dispersoids in the oxide dispersed strengthened steels or alloys,which can be used in nuclear reactors and supercritical boilers.For the first time,HEP oxides Y_(2)(TiZrHfMoV)_(2)O_(7) were synthesized with Y_(2)Ti_(2)O_(7) as a base structure with the B site(Ti)substituted with five cations through reverse co-precipitation technique in the nanocrystalline form at lowest synthesis temperature.The synthesis parameters for Y_(2)(TiZrHfMoV)_(2)O_(7)(5C)and other derived compositions(five compositions of four cationic systems with each cation eliminated at B site from 5 C)are optimised to obtain lower crystallite and particle sizes.5C has a smaller crystallite size(27 nm)than other single-phase compositions.The cation’s influence,oxidation state,and oxygen vacancy in the phase formation were analysed through XPS.The single-phase HEPs are consolidated through spark plasma sintering.Y_(2)(TiZrHfMo)_(2)O_(7)(4 C-V)shows the highest hardness among the compositions reported so far due to its finer grain size,and Y_(2)(TiHfMoV)_(2)O_(7)(4 C-Zr)has a higher Young’s modulus compared to other single-phase composition due to its higher degree of order in the structure.