A Congruent-Melt Infrared Nonlinear Optical Crystal NaSrAsS.

A quaternary metal thioarsenate infrared (IR) nonlinear optical (NLO) compound NaSrAsS was successfully prepared by a high-temperature reaction method from stoichiometric agents. It crystallizes in the tetragonal 42 with the unit cell parameters = 10.0393(3) Å, = 6.9638(3) Å, and = 2, with the basic structural groups of isolated AsS tetrahedra. Compared with benchmark IR NLO crystal AgGaS (AGS), the title compound exhibits balanced optical properties of large band gap (3.05 eV vs. 2.60 eV) and considerable second harmonic generation response (0.95 × AGS). Moreover, the combined powder X-ray diffraction and differential scanning calorimetry analyses demonstrate that NaSrAsS is a congruent-melting compound with a low melting point of 668 °C, which is benefical for bulk single crystal growth. Experimental and theoretical calculation results indicate that NaSrAsS is a practically usable IR NLO crystal, also motivating the exploration of thioarsenates as high-performance IR NLO candidates.