First‐Principles Investigation About Different Sequence of Stereochemical Activity and Birefringence in Antimony Halides

Birefringent compounds play an indispensable role in modern optoelectronics and information communication. In this article, the electronic structures and birefringence of binary and ternary antimony halides are investigated using the first‐principles method. The results show that the stereochemical activity of antimony cations in these compounds gradually decreases from Cl to I, and the birefringence of these compounds gradually increases from Cl to I. The degree of stereochemical activity of lone pairs is determined by the energy difference between the s‐state of the cation and the p‐state of the halogen, implying the revised model about stereochemical activity of lone‐pairs in metal oxides is also appropriate for metal halides. The real‐space atomic cutting and Born effective charges show that the antimony cations and halogen closer to Fermi level give main contribution to birefringence. And the occupied p‐states of antimony and halogen atoms play an important role in determining the birefringence. The stereochemical activity of antimony cations in binary and ternary antimony halides decreases from Cl to I, while the birefringence increases from Cl to I. The p‐states occupied by antimony and halogen atoms determine the birefringence, making the lone‐pair stereochemical activity model suitable for metal halides.