Simple aliovalent cation substitution to induce strong optical anisotropy enhancement in a rare thioantimonate(v) family

Abstract

Thioantimonates containing high oxidation state Sb⁵⁺ have been proven to exhibit excellent performance in the design of new materials such as infrared optical crystals and lithium-ion batteries. However, as described by the “inert pair effect”, the preparation of P-block elements containing high oxidation states in sealed systems has been a challenge. In this study, an aliovalent cation substitution strategy was used to design and synthesize three novel thioantimonates(V), A₄BaSb₂Se₈ (A = Cs, Rb) and Rb₂BaSbS₄Cl (RBSSC), respectively, all of which contain rare [SbS₄] tetrahedral units. The introduction of Ba²⁺ ions leads to the distortion and high-density arrangement of [SbSe₄] units, which is manifested as a significant 3.7 times enhancement of the birefringence compared to that of the parent compound Cs₃SbSe₄ (0.041 → Cs₄BaSb₂Se₈ 0.150@1064 nm). By further introducing highly electronegative halogen atoms, the first antimony-based thiohalide(V) RBSSC was synthesized. Theoretical calculations show that the band gap of RBSSC is up to 3.674 eV, larger than those of all known antimony-based thiohalides(III). This work provides strong evidence that the aliovalent cation substitution strategy is an effective way to find new thioantimonate(V) families, and also indicates that the cation size effect introduced by elemental substitution may lead to surprising performance improvements.