HBa_2.5(IO₃)₆(I₂O₅) and HBa(IO₃)(I₄O₁₁): Explorations of Second-Order Nonlinear Optical Materials in the Alkali-Earth Polyiodate System

Two new barium polyiodate compounds in the alkali-earth system, namely, HBa2.5(IO3)6(I2O5) (Fdd2) and HBa­(IO3)­(I4O11) (P1̅) have been obtained through hydrothermal reaction. Interestingly, the structures of both compounds feature different polyiodate groups, i.e., I2O5 and I4O11 groups. HBa2.5(IO3)6(I2O5) can be depicted as an alternative stacking of two-dimensional (2D) [Ba4(IO3)8(I2O5)2] and [Ba­(IO3)4(I2O5)2]2– layers with the I2O5 and IO3 group serving as linkers. HBa­(IO3)­(I4O11) can be depicted as a 3D network with 2D [Ba­(I4O11)] layers being interconnected by IO3 groups. The 0D I4O11 polyiodate group can be seen also viewed as formed by an I3O8 group further corner-sharing with an IO3 group or an I2O5 group further corner-sharing with two IO3 groups. Powder second harmonic generation (SHG) measurements show that HBa2.5(IO3)6(I2O5) crystals display a moderate SHG efficiency of ∼1.6 times that of KH2PO4 (KDP) and are phase-matchable. Optical properties measurements, thermal analyses, and laser damage threshold (LDT) measurements have been performed. Results of theoretical calculation show that the formation of I4O112– is thermodynamically much easier than I3O8– and I2O5, because of the lower reaction energy. Our studies shed light on exploring alkali-earth polyiodates as potential NLO materials