Li-metal pyrophosphates have been recently reported as novel polyanionic cathode materials with competent electrochemical properties. The current study presents a detailed analysis of inherent electrochemical properties of mixed-metal pyrophosphates, Li2(Fe1–y Mn y )P2O7, synthesized by an optimized solid-state route. They form a complete solid solution assuming a monoclinic framework with space group P21/c. The electrochemical analysis of these single-phase pyrophosphates shows absence of activity associated with Mn, where near-theoretical redox activity associated with Fe metal center was realized around 3.5 V. We noticed a closer look revealed the gradual substitution of Mn into parent Li2FeP2O7 phase triggered a splitting of Fe3+/Fe2+ redox peak and partial upshifting in Fe3+/Fe2+ redox potentials nearing 4.0 V. Introduction of Mn into the pyrophosphate structure may stabilize the two distinct Fe3+/Fe2+ redox reactions by Fe ions in octahedral and trigonal-bipyramidal sites. Increase of the Gibb’s free energy at charged state by introducing Li+–Fe3+ and/or Li vacancy–Mn2+ pairs can be the root cause behind redox upshift. The underlying electrochemical behavior has been examined to assess these mixed-metal pyrophosphates for usage in Li-ion batteries.

Mixed‐metal Li2MxFe1‐xP2O7 (M: Mn, Co, Mg) cathode materials for lithium ion batteries with a monoclinic structure (space group P21/c) exhibit unusually high Fe3+/Fe2+ redox potentials close to 4.0 V vs Li/Li+.

Doped polycrystalline SiC films were deposited from a SiH4-CH4-H2-(PH3 or N2) mixture by plasma-enhanced chemical vapor deposition at 700 °C. The best crystallinity was obtained at x∼0.53 in Si1−xCx for both undoped and doped films. The crystallinity was enhanced by both P and N doping, but deteriorated again under high doping conditions. Also, better crystallinity was obtained by doping with P rather than N. Intrinsic tensile and compressive stresses were observed for P- and N-doped films, respectively. The resistivity and dangling-bond density decreased in correspondence to the enhancement in crystallinity. Origins of the dangling bonds and of a change in the crystallinity were discussed.

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