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991.
The olivine type LiMPO4 (M=Ni, Mn and Co) materials were synthesized by solution combustion technique using glycine as fuel. The structural characterizations were explored to confirm the phase formation of materials. The scanning electron microscope was used to identify the morphology of olivine materials. The local structure and chemical bonding between MO6 octahedral and (PO4)3- tetrahedral groups were probed by Raman spectroscopy. Grain and grain boundaries were contributed for ion relaxation and dc conduction in olivine materials. Two orders of enhancement in ionic conductivity was observed in these olivine materials than the reported value. Among all the explored olivine samples, LiMnPO4 showed highest enhancement in conductivity due to weak Li–O bonding and largest unit cell volume. 相似文献
992.
The Ruddlesden–Popper phases of the Ca–Ti–O system, Can+1TinO3n+1, are investigated by means of atomistic simulations employing empirical pair potentials. The stability of the phases is examined in terms of various reaction schemes: the formation from the binary oxides, the addition of the perovskite oxide to a given phase, and the reaction between perovskite and rock-salt oxides. The energies of these reactions are compared with results previously obtained for the Ruddlesden–Popper phases of the Sr–Ti–O system. The importance of the disproportionation reaction of the various R–P phases in both Ca and Sr systems is also emphasized. The results obtained are in good agreement with experimental observations regarding both systems. 相似文献
993.
A series of hard carbons was produced by the carbonization of microcrystalline cellulose powder in the temperature range of 950–1100 °C. The properties of the carbons were characterized using elemental analysis, X-ray diffraction and N2 and CO2 adsorption. The effect of heat-treatment temperature (HTT), pyrolytic carbon (PC) coating and discharging mode on the lithium insertion/deinsertion behavior of the carbons was assessed in a coin-type half-cell with metal lithium cathode. Increasing cellulose HTT modifies mostly carbon porosity, the surface area (SDFT) decreases from about 500 to 167 m2 g−1. It is associated with lowering the reversible Crev and irreversible Cirr capacities, but without improving relatively low (0.72) 1st cycle coulombic efficiency. Applying constant current (CC)+constant voltage (CV) discharging mode instead of conventional CC enhances the reversible capacity by 15–18%. PC coating is effective in reducing Cirr by ∼20% with a little change of Crev. The best capacity parameters, Crev of 458 mA h g−1 and Cirr of 139 mA h g−1, were measured for PC coated 1000 °C carbon. The prolonged cycling of full-cell assembled with anode of the carbon and commercial cathode revealed that after initial 20 cycles the capacity decay (0.029 mA h/cycle) is comparable to that of commercial cell with graphite-based anode. 相似文献
994.
Nano-structured LiVPO4F/Ag composite cathode material has been successfully synthesized via a sol–gel route. The structural and physical properties, as well as the electrochemical performance of the material are compared with those of the pristine LiVPO4F. X-ray diffraction (XRD) and scanning electron microscopy (SEM) reveal that Ag particles are uniformly dispersed on the surface of LiVPO4F without destroying the crystal structure of the bulk material. An analysis of the electrochemical measurements show that the Ag-modified LiVPO4F material exhibits high discharge capacity, good cycle performance (108.5 mAh g−1 after 50th cycles at 0.1 C, 93% of initial discharge capacity) and excellent rate behavior (81.8 mAh g−1 for initial discharge capacity at 5 C). The electrochemical impedance spectroscopy (EIS) results reveal that the adding of Ag decreases the charge-transfer resistance (Rct) of LiVPO4F cathode. This study demonstrates that Ag-coating is a promising way to improve the electrochemical performance of the pristine LiVPO4F for lithium-ion batteries cathode material. 相似文献
995.
In this work, we reported the effect of Li2CO3 addition on the structural, optical, ferroelectric properties and electric-field-induced strain of Bi0.5(Na,K)0.5TiO3 (BNKT) solid solution with CaZrO3 ceramics. Both rhombohedral and tetragonal structures were distorted after adding Lithium (Li). The band gap values decreased from 2.91 to 2.69 eV for 5 mol% Li-addition. The maximum polarization and remanent polarization decreased from 49.66 μC/cm2 to 27.11 μC/cm2 and from 22.93 μC/cm2 to 5.35 μC/cm2 for un-doped and 5 mol% Li- addition BNKT ceramics, respectively. The maximum Smax/Emax value was 567 pm/V at 2 mol% Li2CO3 access. We expected this work will help to understand the role of A-site dopant in lead-free ferroelectric BNKT materials. 相似文献
996.
The present study reports the influence of pre-carbonization on the properties of KOH-activated coal tar pitch (CTP). The change of crystallinity and pore structure of pre-carbonized CTPs as well as their activated carbons (ACs) as function of pre-carbonization temperature are investigated. The crystallinity of pre-carbonized CTPs increases with increasing the carbonization temperature up to 600 °C, but a disorder occurs during the carbonization around 700 °C and an order happens gradually with increasing the carbonization temperatures in range of 800–1000 °C. The CTPs pre-carbonized at high temperatures are more difficult to be activated with KOH than those pre-carbonized at low temperatures due to the increase of micro-crystalline size and the decrease of surface functional groups. The micro-pores and meso-pores are well developed at around 1.0 nm and 2.4 nm, respectively, as the ACs are pre-carbonized at temperatures of 500–600 °C, exhibiting high specific capacitances as electrode materials for electric double layer capacitor (EDLC). Although the specific surface area (SSA) and pore volume of ACs pre-carbonized at temperatures of 900–1000 °C are extraordinary low (non-porous) as compared to those of AC pre-carbonized at 600 °C, their specific capacitances are comparable to each other. The large specific capacitances with low SSA ACs can be attributed to the structural change resulting from the electrochemical activation during the 1st charge above 2.0 V. 相似文献
997.
Mamta Chauhan 《Phase Transitions》2015,88(12):1193-1212
The structural, electronic, mechanical, phase transition, and thermo-physical properties of refractory carbides, viz. VC, NbC, and TaC have been computed in stable B1 and high pressure B2 phases by means of two different ab initio calculations using pseudo- and full-potential schemes. These materials have mixed covalent-, metallic-, and ionic-type bonding. The calculations of elastic constants show the mechanical stability of these materials in B1 phase only. The brittle nature and anisotropy is observed in these materials in B1 phase. Non-central forces are present in both the phases. Elastic wave velocities and Debye temperature have also been calculated. The present results on structural, phase transition, elastic, and other properties are in reasonably good agreement with the available experimental and theoretical data. The calculations in high pressure phase need experimental verification. 相似文献
998.
Monika Karpierz Jan Suchanicz Krzysztof Konieczny Dorota Sitko Pascal Marchet Urszula Lewczuk 《Phase Transitions》2015,88(7):662-667
The 0.5K0.5Bi0.5TiO3–0.5PbTiO3 ceramics were prepared by following a standard solid-state method. The Raman, thermal and dielectric properties of these ceramics were investigated. The X-ray measurements showed that samples have single perovskite-type structure with tetragonal symmetry. Dielectric study revealed that the dielectric behaviour of the investigated ceramics is rather of normal ferroelectrics with large thermal hysteresis. The transition temperature observed by means of differential scanning calorimetry measurements is in good agreement with that obtained from dielectric study. 相似文献
999.
讨论了Zn O对Ba Sm2Ti4O12介质陶瓷烧结机制和微波介电性能的影响。结果表明:Zn O添加能推动Ba Sm2Ti4O12微波介质陶瓷的烧结,可至少将其烧结温度降低至1 280℃。当添加过多的Zn O时,Zn2+会进入晶格,可能导致晶格畸变,由此造成颗粒间产生微小孔隙及晶格内形成许多缺陷,降低了材料的εr和Q×f值。含0.5 wt%Zn O的Ba Sm2Ti4O12试样在1 280℃烧结时,综合介电性能最好:εr=76.46,Q×f=6 334 GHz。 相似文献
1000.