The Layered Structure–Induced Enhanced Birefringence of LiMgPO 4 : A First‐Principles Investigation

Phosphates are thought to be good candidates as ultraviolet/deep ultraviolet optical materials due to their large bandgap and excellent optical properties. Through first‐principles screening of a series of alkali/alkaline earth metal phosphates containing isolated PO 4 tetrahedra, LiMgPO 4 is identified as a promising candidate. It exhibits not only a wide bandgap (7.478 eV) but also a moderate birefringence of 0.045 at 1064 nm. Notably, this birefringence is approximately five times that of Pb 5 (PO 4 ) 3 Cl, which contains Pb 2+ cations with lone‐pair electrons. The structural analysis shows that LiMgPO 4 has a unique LiPO‐layered structure. In addition, electronic structure analysis, including band structure, real‐space atom‐cutting (RSAC) method, and Born effective charge analysis, also confirm the role of LiPO layers in enhancing optical properties. In a word, this layered structure not only promotes bandgap broadening but is also considered the primary contributor to its enhanced birefringence.