Novel antimony phosphates with enlarged birefringence induced by lone pair cations

Novel centrosymmetric compounds, Cs 2 Sb 3 O(PO 4 ) 3 and (NH 4 ) 2 Sb 4 O 2 (H 2 O)(PO 4 ) 2 [PO 3 (OH)] 2 , were successfully obtained. It is shown that the birefringence is significantly enhanced by the introduction of the Sb 3+ cations, and still has a wide band gap.