Supertetrahedral Networks and Lithium-Ion Mobility in Li2SiP2 and LiSi2P3

摘要

The new phosphidosilicates Li2SiP2 and LiSi2P3 were synthesized by heating the elements at 1123K and characterized by single-crystal X-ray diffraction. Li2SiP2 (I4(1)/acd, Z=32, a=12.111(1)angstrom, c=18.658(2)angstrom) contains two interpenetrating diamond-like tetrahedral networks consisting of corner-sharing T2 supertetrahedra [(SiP4/2)(4)]. Sphalerite-like interpenetrating networks of uniquely bridged T4 and T5 supertetrahedra make up the complex structure of LiSi2P3 (I4(1)/a, Z=100, a=18.4757(3)angstrom, c=35.0982(6)angstrom). The lithium ions are located in the open spaces between the supertetrahedra and coordinated by four to six phosphorus atoms. Temperature-dependent Li-7 solid-state MAS NMR spectroscopic data indicate high mobility of the Li+ ions with low activation energies of 0.10eV in Li2SiP2 and 0.07eV in LiSi2P3.