Birefringent　materials　have　been　widely　used　in　optical　devices.　An　excellent　birefringent　material,　HfF2(IO3)2,　was　rational　designed　and　synthesized　by　integrating　iodate　and　fluoride　functional　groups.　HfF2(IO3)2　inherits　the　huge　optical　anisotropy　of　iodates　and　the　wide　energy　gap　of　fluorides　and　possesses　outstanding　properties　including　a　large　birefringence　of　0.333　and　a　wide　energy　gap　of　4.11　eV　(a　short　ultraviolet　absorption　cutoff　edge　of　253　nm),　superior　to　the　commercial　birefringent　crystals　such　as　YVO4　(Δn,　0.204　at　532　nm;　Eg,　3.10　eV)　and　TiO2　(Δn,　0.256　at　1530　nm;　Eg,　3.20　eV).　HfF2(IO3)2　also　has　a　high　thermal　stability　and　a　wide　transparent　spectral　range,　and　it　is　non-hygroscopic.　Our　investigations　showed　that　the　birefringences　are　linearly　proportional　to　the　parallelisms　and　the　spatial　densities　of　the　functional　lone-pair　groups.　This　work　demonstrates　that　combining　functional　groups　is　an　effective　strategy　for　designing　promising　inorganic　functional　materials.　©　2022