High energy mechanical milling （HEMM） of a stoichiometric mixture of molybdenum and metal chalcogenides （CuT and MOT2; T = S, Se） followed by heat treatment at elevated temperatures was successfully applied to syn...High energy mechanical milling （HEMM） of a stoichiometric mixture of molybdenum and metal chalcogenides （CuT and MOT2; T = S, Se） followed by heat treatment at elevated temperatures was successfully applied to synthesize Chevrel phases （Cu2Mo6T8; T = S, Se） as positive electrodes for rechargeable magnesium batteries. Differential scanning calorimetry （DSC）, thermogravimetric analyses （TGA）, X-ray diffraction （XRD）, and scanning electron microscopy （SEM） were used to understand the phase formation following milling and heat treatment. CuS and Mo were observed to react at 714-800 K and formed an intermediate ternary Chevrel phase （Cu1.83Mo3S4）, which further reacted with residual Mo and MoS2 to form the desired Cu2MosSs. Quantitative XRD analysis shows the formation of a -96%-98% Chevrel phase at 30 min following the milling and heat treatment. The electrochemical performance of de-cuprated Mo6S8 and Mo6Ses phases were evaluated by cyclic voltammetry （CV）, galvanostatic cycling, and electrochemical impedance spectroscopy （EIS）. The results of the CV and galvanostatic cycling data showed the expected anodic/cathodic behavior and a stable capacity after the first cycle with the formation of MgxMo6T8 （T = S, Se; 1 ≤ x 〈 2）. EIS at -0.1 V intervals for the Mo6Ss electrode during the first and second cycle shows that partial Mg-ion trapping resulted in an increase in charge transfer resistance Re. In contrast, the interfacial resistance Ri remained constant, and no significant trapping was evident during the galvanostatic cycling of the Mo6,Se8 electrode. Importantly, the ease of preparation, stable capacity, high Coulombic efficient35 and excellent rate capabilities render HEMM a viable route to laboratory-scale production of Chevrel phases for use as positive electrodes for rechargeable magnesium batteries.展开更多
Ag and Cu filled Chevrel phase MxMo6Te8 (x=1.0, 2.0) samples were synthesized by direct solid state reaction and spark plasma sintering. The electrical and thermal properties were investigated in the temperature range...Ag and Cu filled Chevrel phase MxMo6Te8 (x=1.0, 2.0) samples were synthesized by direct solid state reaction and spark plasma sintering. The electrical and thermal properties were investigated in the temperature range of 300-800 K. The results show that both the electrical and thermal properties are affected by filler atoms. Although the electrical conductivity of MxMo6Te8 is slightly higher than that of state-of-the-art thermoelectric material, such as filled skutterudites, the absolute value of Seebeck coefficient is relatively low. Due to the phonon scattering by the filler atoms, the decrease of the thermal conductivity and the lattice thermal conductivity is obvious. As a result, the dimensionless figure of merit(ZT) is improved over the whole temperature region. The highest ZT value is 0.034 at 800 K for the AgMo6Te8 sample.展开更多
Here we report the discovery of the first ternary molybdenum pnictide based superconductor K2Mo3As3. Polycrystalline samples were synthesized by the conventional solid state reaction method. X-ray diffrac- tion analys...Here we report the discovery of the first ternary molybdenum pnictide based superconductor K2Mo3As3. Polycrystalline samples were synthesized by the conventional solid state reaction method. X-ray diffrac- tion analysis reveals a quasi-one-dimensional hexagonal crystal structure with （Mo3As3）2 linear chains separated by K^＋ ions, similar as previously reported K2Cr3As3, with the space group of P-6m2 （No. 187） and the refined lattice parameters a = 10.145（5） A and c = 4.453（8） A. Electrical resistivity, magnetic susceptibility, and heat capacity measurements exhibit bulk superconductivity with the onset Tc at 10.4 K in K2Mo3As3 which is higher than the isostructural Cr-based superconductors. Being the same group VIB transition elements and with similar structural motifs, these Cr and Mo based superconductors may share some common underlying origins for the occurrence of superconductivity and need more investigations to uncover the electron pairing within a quasi-one-dimensional chain structure.展开更多
文摘High energy mechanical milling （HEMM） of a stoichiometric mixture of molybdenum and metal chalcogenides （CuT and MOT2; T = S, Se） followed by heat treatment at elevated temperatures was successfully applied to synthesize Chevrel phases （Cu2Mo6T8; T = S, Se） as positive electrodes for rechargeable magnesium batteries. Differential scanning calorimetry （DSC）, thermogravimetric analyses （TGA）, X-ray diffraction （XRD）, and scanning electron microscopy （SEM） were used to understand the phase formation following milling and heat treatment. CuS and Mo were observed to react at 714-800 K and formed an intermediate ternary Chevrel phase （Cu1.83Mo3S4）, which further reacted with residual Mo and MoS2 to form the desired Cu2MosSs. Quantitative XRD analysis shows the formation of a -96%-98% Chevrel phase at 30 min following the milling and heat treatment. The electrochemical performance of de-cuprated Mo6S8 and Mo6Ses phases were evaluated by cyclic voltammetry （CV）, galvanostatic cycling, and electrochemical impedance spectroscopy （EIS）. The results of the CV and galvanostatic cycling data showed the expected anodic/cathodic behavior and a stable capacity after the first cycle with the formation of MgxMo6T8 （T = S, Se; 1 ≤ x 〈 2）. EIS at -0.1 V intervals for the Mo6Ss electrode during the first and second cycle shows that partial Mg-ion trapping resulted in an increase in charge transfer resistance Re. In contrast, the interfacial resistance Ri remained constant, and no significant trapping was evident during the galvanostatic cycling of the Mo6,Se8 electrode. Importantly, the ease of preparation, stable capacity, high Coulombic efficient35 and excellent rate capabilities render HEMM a viable route to laboratory-scale production of Chevrel phases for use as positive electrodes for rechargeable magnesium batteries.
基金Projects(2007CB607502, 2007CB607503) supported by the National Basic Research Program of China
文摘Ag and Cu filled Chevrel phase MxMo6Te8 (x=1.0, 2.0) samples were synthesized by direct solid state reaction and spark plasma sintering. The electrical and thermal properties were investigated in the temperature range of 300-800 K. The results show that both the electrical and thermal properties are affected by filler atoms. Although the electrical conductivity of MxMo6Te8 is slightly higher than that of state-of-the-art thermoelectric material, such as filled skutterudites, the absolute value of Seebeck coefficient is relatively low. Due to the phonon scattering by the filler atoms, the decrease of the thermal conductivity and the lattice thermal conductivity is obvious. As a result, the dimensionless figure of merit(ZT) is improved over the whole temperature region. The highest ZT value is 0.034 at 800 K for the AgMo6Te8 sample.
基金supported by the National Natural Science Foundation of China(11474339 and 11774402)the National Basic Research Program of China(973 Program,2016YFA0300301)the Youth Innovation Promotion Association of the Chinese Academy of Sciences
文摘Here we report the discovery of the first ternary molybdenum pnictide based superconductor K2Mo3As3. Polycrystalline samples were synthesized by the conventional solid state reaction method. X-ray diffrac- tion analysis reveals a quasi-one-dimensional hexagonal crystal structure with （Mo3As3）2 linear chains separated by K^＋ ions, similar as previously reported K2Cr3As3, with the space group of P-6m2 （No. 187） and the refined lattice parameters a = 10.145（5） A and c = 4.453（8） A. Electrical resistivity, magnetic susceptibility, and heat capacity measurements exhibit bulk superconductivity with the onset Tc at 10.4 K in K2Mo3As3 which is higher than the isostructural Cr-based superconductors. Being the same group VIB transition elements and with similar structural motifs, these Cr and Mo based superconductors may share some common underlying origins for the occurrence of superconductivity and need more investigations to uncover the electron pairing within a quasi-one-dimensional chain structure.
