The enhancement of birefringence resulted from anionic dimensionality changes through adjusting cationic density

Abstract

Single crystals of a new series of alkaline metal molybdates, LiNa3(MoO4)2 and LiAMo3O10 (A = K+, Rb+, Cs+), have been successfully synthesized through conventional high-temperature solid-state reactions. The compounds are structurally characterized by single-crystal X-ray diffraction and exhibit three-dimensional (3D) crystal structures consisting of 0D or 1D MoO framework. Interestingly, when MoO dimensionality changes from 0D of LiNa3(MoO4)2 to 1D of LiAMo3O10, the birefringence of LiAMo3O10 is significantly enhanced to as large as BaTeMo2O9 and Na2TeW2O9. The differences of bandgaps induced by anionic-group dimensionality are also discussed based on structural and theoretical analyses, which illuminate that the bandgap tends to be relatively broad for compounds with isolated MoO4 tetrahedra in alkaline metal molybdate family. In addition, the dimensional reduction formalism was applied in the alkaline metal molybdate system to explore the changes of MoO framework along with cation/Mo ratio for the first time.