Polar materials are of great technical interest but challenging to effectively synthesize. That is especially true for iodates, an important class of visible and mid-IR transparent nonlinear optical (NLO) materials. Aiming at developing a new design strategy for polar iodates, we successfully synthesized two sets of polymorphic early transition-metal (ETM) oxide-fluoride iodates, α- and β-Ba[VFO 2 (IO 3 ) 2 ] and α- and β-Ba 2 [VO 2 F 2 (IO 3 ) 2 ]IO 3 , based on the distinct structure-directing properties of oxide-fluoride anions. α- and β-Ba[VFO 2 (IO 3 ) 2 ] contain the trans-[VFO 2 (IO 3 ) 2 ] 2- polyanion and crystallize in the nonpolar space groups Pbcn and P2 1 2 1 2 1 . In contrast, α- and β-Ba 2 [VO 2 F 2 (IO 3 ) 2 ]IO 3 contain the cis-[VO 2 F 2 (IO 3 ) 2 ] 3- λ-shaped polyanion and crystallize in the polar space groups Pna2 1 and P2 1 , respectively. Detailed structural analyses show that the variable polar orientation of trans-[VFO 2 (IO 3 ) 2 ] 2- polyanions is the main cause of the nonpolar structures in α- and β-Ba[VFO 2 (IO 3 ) 2 ]. However, the λ-shaped configuration of cis-[VO 2 F 2 (IO 3 ) 2 ] 3- polyanions can effectively guarantee the polar structures. Further property measurements show that polar α- and β-Ba 2 [VO 2 F 2 (IO 3 ) 2 ]IO 3 possess excellent NLO properties, including the large SHG responses (∼9 × KDP), wide visible and mid-IR transparent region (∼0.5-10.5 μm), and high thermal stability (up to 470 °C). Therefore, combining cis-directing oxide-fluoride anions and iodates is a viable strategy for the effective design of polar iodates.
ASJC Scopus subject areas
- Colloid and Surface Chemistry