AAl(Te 4 O 10 ) (A = Na, Ag) and K 2 Ga 2 (HTe 6 O 16 )(HTeO 3 ): Three Aluminum/Gallium Tellurites with Large Birefringence and Wide Band Gap.

The exploration of novel inorganic tellurites is significant because of their promising applications in nonlinear-optical materials and birefringent materials. Herein, three new aluminum/gallium tellurites, namely, NaAl(Te 4 O 10 ) ( 1 ), AgAl(Te 4 O 10 ) ( 2 ), and K 2 Ga 2 (HTe 6 O 16 )(HTeO 3 ) ( 3 ), have been successfully obtained by mild hydrothermal reactions. The isostructural compounds 1 and 2 contain the Te 3 O 8 trimer, while compound 3 contains an unprecedented Te 6 O 16 hexamer. Notably, all three compounds exhibit large birefringence values of over 0.1 at 532 nm, which are currently the largest reported birefringence values among tellurium(IV) oxides without additional anionic groups.