Crystal structure of a new polymorph of Li2FeSiO4.

We report on the crystal structure of a new polymorph of Li(2)FeSiO(4) (prepared by annealing under argon at 900 degrees C and quenching to 25 degrees C) characterized by electron microscopy and powder X-ray and neutron diffraction. The crystal structure of Li(2)FeSiO(4) quenched from 900 degrees C is isostructural with Li(2)CdSiO(4), described in the space group Pmnb with lattice parameters a = 6.2836(1) A, b = 10.6572(1) A, and c = 5.0386(1) A. A close comparison is made with the structure of Li(2)FeSiO(4) quenched from 700 degrees 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 FeO(4) and SiO(4) tetrahedra.