ASbF3Cl (A = Rb, Cs): Structural Evolution from Centrosymmetry to Noncentrosymmetry

The alkali metals Rb+ and Cs+ involving structural evolution from centrosymmetric (CS) to noncentrosymmetric (NCS) is investigated in the ASbF3Cl compounds. RbSbF3Cl crystallizes in the orthorhombic centrosymmetric space group of Pbca, whereas CsSbF3Cl crystallizes in the tetragonal noncentrosymmetric space group of I4̅2m, although they both consist of [SbF3Cl2] units and alkali metal cations. The CS to NCS evolution is originated from the structural dimensional reduction owing to the accommodation of the relatively larger alkali metal cations. RbSbF3Cl and CsSbF3Cl are stable under 195 and 205 °C, respectively, and their energy band gaps are about 3.30 and 3.05 eV. Powder second harmonic generation (SHG) measurements show that CsSbF3Cl is phase-matchable with a response of 0.3 times that of KH2PO4. Moreover, first-principles calculations are performed to investigate the origin of SHG effects in CsSbF3Cl.