HBa2.5(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) (P (1) over bar) have been obtained through hydro-thermal 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) [Ba-4(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 OD 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 similar to 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.