RbMo2P3O14 with large birefringence mainly induced by highly distorted [MoO6] in uncommon [Mo2P3O14]∞ layers

The introduction of d0 transition metal Mo6+ cations into a phosphate generates a new acentric molybdophosphate, RbMo2P3O14. It shows uncommon [Mo2P3O14]∞ layers composed of isolated [MoO6] octahedra and [P3O10] groups. To the best of our acknowledge, it exhibits the largest birefringence (a calculated value of 0.166 at 546 nm) among reported molybdophosphates. In addition, it also possesses a shorter UV cut-off edge (about 250 nm) than other molybdates and molybdophosphates, indicating that it can be used as a birefringent crystal in the UV optical region. First-principles electronic structure analysis suggests that the large birefringence mainly originates from highly distorted [MoO6].