Bi(SO 4 )F·H 2 O and Bi(SO 4 )(NO 3 )·3H 2 O: Chemical Substitution-Induced Birefringence Enhancement in Bismuth Sulfates.

Two new Bi(III)-based sulfates, namely, Bi(SO 4 )F·H 2 O (BSOF) and Bi(SO 4 )(NO 3 )·3H 2 O (BSNO), have been successfully synthesized through aliovalent replacement of partial [SO 4 ] 2- groups with F - and [NO 3 ] - anions, respectively, in the parent structure of Bi 2 (SO 4 ) 3 . Such chemical replacement altered the coordination environment of Bi 3+ cations, facilitating changes in the structure and optical properties. Notably, the birefringence values of BSOF and BSNO are found to be 4.4 and 15.5 times that of parent Bi 2 (SO 4 ) 3 . Further investigation into the structure-property relationship revealed that the birefringence enhancement in BSOF and BSNO is attributed to the improvement of the polarizability anisotropy of Bi 3+ -centered polyhedra in BSOF and BSNO compared to that of Bi 2 (SO 4 ) 3 . In addition, the existence and optimized arrangement of planar [NO 3 ] - groups are also indispensable for further birefringence improvement of the BSNO compound.