Three Rare‐Earth Metal Borates Synthesized via a Cation Substitution Strategy as Potential Zero‐Order Waveplate Materials

ABSTRACT Zero‐order waveplates, as a crucial component of polarization optics, play a significant role in numerous frontier fields. Currently, there are few materials for zero‐order waveplates that simultaneously possess short UV cutoff edges, small birefringence, and stable physicochemical properties. Therefore, research on zero‐order waveplate materials is urgently needed. In this study, we selected the [B 5 O 10 ] group as the building block and synthesized three new borates (Rb 7 CdY 2 B 15 O 30 , K 6 NaSrLu 2 B 15 O 30 , and K 4.6 Rb 2.4 CaSc 2 B 15 O 30 ) through a cation substitution strategy. They feature short UV cutoff edges and excellent thermal stability. Notably, Rb 7 CdY 2 B 15 O 30 and K 4.6 Rb 2.4 CaSc 2 B 15 O 30 exhibit ultra‐small birefringence (0.006@532 nm), with values smaller than the 0.0092@532 nm of standard zero‐order waveplate quartz, and consequently they hold promise for zero‐order waveplate applications. In addition, it can be inferred that [B 5 O 10 ] is a potential group that may be useful in the search for zero‐order waveplate materials.