Crystal structure of Li2MgSiO4

The crystal structure of Li2MgSiO4 was established by single-crystal X-ray diffraction analysis. The crystals are monoclinic, a = 4.9924(7) A, b = 10.681(2) A, c = 6.2889(5) A, β = 90.46(1)°, Z = 4, sp. gr. P21/n, V = 335.54 A3, R = 0.062. In a Li2MgSiO4 crystal, four types of independent T(1–4) tetrahedra share vertices to form a three-dimensional framework. Three of these tetrahedra are occupied simultaneously by Li and Mg cations, which corresponds to the crystallochemical formula (Li0.98Mg0.02)(Li0.80Mg0.20) · (Li0.22Mg0.78)SiO4. In slightly distorted SiO4 tetrahedra denoted as T(1), the average Si-O distance is 1.635(2) A. The distortions of other tetrahedra and the average (Li x Mg1 − x)-O distances increase with an increase in lithium content. These distances in the T(2), T(3), and T(4) tetrahedra are 1.955(2), 1.971(4), and 2.019(6) A, respectively. The structure of the new compound is compared with the crystal structures of other Li2M2+SiO4 compounds and the luminescence spectra of Cr4+: Li2MgSiO4.