Excellent Infrared Nonlinear Optical Crystals BaMO(IO₃)₅ (M = V, Ta) Predicted by First Principle Calculations

Two nonlinear optical crystals, BaVO(IO₃)₅ and BaTaO(IO₃)₅, are designed by substituting Nb with V and Ta, respectively, in BaNbO(IO₃)₅, which is itself a recently synthesized infrared nonlinear optical (NLO) material. The designs of BaVO(IO₃)₅ and BaTaO(IO₃)₅ from BaNbO(IO₃)₅ are based on the following motivation: BaVO(IO₃)₅ should have a larger second-harmonic generation (SHG) coefficient than BaNbO(IO₃)₅, as V will result in a stronger second-order Jahn-Teller effect than Nb due to its smaller ion radius; at the same time, BaTaO(IO₃)₅ should have a larger laser-damage threshold, due to the fact that Ta has a smaller electronegativity leading to a greater band-gap. Established on reliable first-principle calculations, it is demonstrated that BaVO(IO₃)₅ has a much larger SHG coefficient than BaNbO(IO₃)₅ (23.42 × 10^-9 vs. 18.66 × 10^-9 esu); and BaTaO(IO₃)₅ has a significantly greater band-gap than BaNbO(IO₃)₅ (4.20 vs. 3.55 eV). Meanwhile, the absorption spectra and birefringences of both BaVO(IO₃)₅ and BaTaO(IO₃)₅ are acceptable for practice, suggesting that these two crystals can both be expected to be excellent infrared NLO materials.