68848-64-6Relevant academic research and scientific papers
Site-Specific Substitution Preferences in the Solid Solutions Li12Si7–xGex, Li12–yNaySi7, Na7LiSi8–zGez, and Li3NaSi6–vGev
Scherf, Lavinia M.,Riphaus, Nathalie,F?ssler, Thomas F.
, p. 1143 - 1151 (2016)
The mixed silicide-germanides Li12Si7–xGex, Na7LiSi8–zGez, and Li3NaSi6–vGevwhich could serve as potential precursors for Si1–xGexmaterials were synthesized and characterized by X-ray diffraction methods. The full solid solution series Li12Si7–xGex(0 ≤ x ≤ 7) is easily accessible from the elements and features preferential occupation of the more negatively charged crystallographic tetrel positions by Ge, which is the more electronegative element. In case of Na7LiSi8–zGeza broad solid solution range of 1.3 ≤ x ≤ 8 is available but the ternary silicide Na7LiSi8could not be obtained by the tested methods of synthesis. The solubility of Ge in Li3NaSi6–vGevis highly limited to a maximum of v ≈ 0.5, and again the formally more negatively charged tetrel positions are preferred by Ge. Additionally, the two crystallographic Li positions in Li12Si7with unusually large displacement parameters can be partially substituted by Na in Li12–yNaySi7with 0 ≤ y ≤ 0.6. The statistical mixing of Li and Na in this solid solution contrasts the typical ordering of Li and Na in most ternary tetrelides.
Lithium monosilicide (LiSi), a low-dimensional silicon-based material prepared by high pressure synthesis: NMR and vibrational spectroscopy and electrical properties characterization
Stearns, Linda A.,Gryko, Jan,Diefenbacher, Jason,Ramachandran, Ganesh K.,McMillan, Paul F.
, p. 251 - 258 (2003)
Lithium monosilicide (LiSi) was formed at high pressures and high temperatures (1.0-2.5GPa and 500-700°C) in a piston-cylinder apparatus. This compound was previously shown to have an unusual structure based on 3-fold coordinated silicon atoms arranged into interpenetrating sheets. In the present investigation, lowered synthesis pressures permitted recovery of large (150-200mg) quantities of sample for structural studies via NMR spectroscopy (29Si and 7Li), Raman spectroscopy and electrical conductivity measurements. The 29Si chemical shift occurs at -106.5ppm, intermediate between SiH4 and Si(Si(CH3)3)4, but lies off the trend established by the other alkali monosilicides (NaSi, KSi, RbSi, CsSi), that contain isolated Si44- anions. Raman spectra show a strong peak at 508cm-1 due to symmetric Si-Si stretching vibrations, at lower frequency than for tetrahedrally coordinated Si frameworks, due to the longer Si-Si bonds in the 3-coordinated silicide. Higher frequency vibrations occur due to asymmetric stretching. Electrical conductivity measurements indicate LiSi is a narrow-gap semiconductor (Eb～0.057eV). There is a rapid increase in conductivity above T=450K, that might be due to the onset of Li+ mobility.
Accelerating rate calorimetry studies of the reactions between ionic liquids and charged lithium ion battery electrode materials
Wang, Yadong,Zaghib,Guerfi,Bazito, Fernanda F.C.,Torresi, Roberto M.,Dahn
, p. 6346 - 6352 (2007)
Using accelerating rate calorimetry (ARC), the reactivity between six ionic liquids (with and without added LiPF6) and charged electrode materials is compared to the reactivity of standard carbonate-based solvents and electrolytes with the same electrode materials. The charged electrode materials used were Li1Si, Li7Ti4O12 and Li0.45CoO2. The experiments showed that not all ionic liquids are safer than conventional electrolytes/solvents. Of the six ionic liquids tested, 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMI-FSI) shows the worst safety properties, and is much worse than conventional electrolyte. 1-Ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMI-TFSI) and 1-propyl-1-methylpyrrolidinium bis(fluorosulfonyl)imide (Py13-FSI) show similar reactivity to carbonate-based electrolyte. The three ionic liquids 1-butyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide (BMMI-TFSI), 1-butyl-1-methylpiperidinium bis(trifluoromethanesulfonyl)imide (Pp14-TFSI) and N-trimethyl-N-butylammonium bis(trifluoromethanesulfonyl)imide (TMBA-TFSI) show similar reactivity and are much safer than the conventional carbonate-based electrolyte. A comparison of the reactivity of ionic liquids with common anions and cations shows that ionic liquids with TFSI- are safer than those with FSI-, and liquids with EMI+ are worse than those with BMMI+, Py13+, Pp14+ and TMBA+.
LiSi, a unique Zintl phase - although stable, it long evaded synthesis
Evers, J.,Oehlinger, G.,Sextl, G.
, (2008/10/08)
For more than two decades all attempts have failed to prepare LiSi, the missing first member of the homologous series of stable Zintl phases MSi(M = Na, K, Rb, Cs). However, now it was found that at 40 kbar, 600.deg ree.C synthesis of LiSi is easily performed within 5 min using belt highpressure equipment. X-ray structure analysis shows that LiSi (I41/A, a = 9.353(1), c = 5.743(1)?, z =16) crystallizes in the MgGa type stru cture and is isotypic with LiGe. LiSi builds up a three-dimensional three-connected net with the longest Si-Si bond distances (2.417(6)(2x) and 2.502(6)?) which have ever been determined in lithium silicides by modern diffractin techniques. Difference thermal analysis and coulometrictitration experiments show that LiSi is a thermodynamically stable comp ound at ambient pressure. At 485.+-.10°C and 1 bar it decomposes endothermically into a mixture of Li12Si7 and 5 Si. From X-ray powder investigations both up to 350°C at ambient pressure (Guinier diffractometer, CuKα1 radiation) and up to 58 kbar at ambient temperature (diamond anvil cell diffractometer, AgKα radiation) the following is derived: Under conditions used for synthesis (40 kbar, 600°C) compression of LiSi overcompensates thermal expansion. Thus the decomposition temperature is strongly raised from 485°C at 1 bar to higher than 600°C at 40 kbar.
