Structural Refinement of Olivine-Type LiMgAsO₄

Abstract

The refinement of the LiMgAsO⁴ structure by powder neutron diffraction confirms that it is isostructural with olivine. The structure is orthorhombic, Pnma space group, with a = 10.4183(15), b = 5.9660(8), c = 4.8692(5) Å, and Z = 4. The lithium and magnesium atoms are fully ordered on the octahedral sites with average bond lengths (Li-O) = 2.187, (Mg-O) = 2.108 and (As-O) = 1.672 A. LiMgAsO₄ is isostructural with LiMgPO₄ but not with LiMgVO₄. However, a close structural relationship exists between the arsenate and the vanadate involving similar cation arrays but different anion arrays.