Crystal Structure of a New Polymorph of Li2FeSiO4

We report on the crystal structure of a new polymorph of Li2FeSiO4 (prepared by annealing under argon at 900 °C and quenching to 25 °C) characterized by electron microscopy and powder X-ray and neutron diffraction. The crystal structure of Li2FeSiO4 quenched from 900 °C is isostructural with Li2CdSiO4, described in the space group Pmnb with lattice parameters a = 6.2836(1) Ǻ, b = 10.6572(1) Ǻ, and c = 5.0386(1) Ǻ. A close comparison is made with the structure of Li2FeSiO4 quenched from 700 °C, published recently by Nishimura et al. (J. Am. Chem. Soc. 2008, 130, 13212). The two polymorphs differ mainly on the respective orientations and alternate sequences of corner-sharing FeO4 and SiO4 tetrahedra.