Synthesis, Crystal Structure, and Characterization of a Noncentrosymmetric Sulfate Cs2Ca2(SO4)3

The noncentrosymmetric structure is one prerequisite of a nonlinear optical (NLO) material. Here, a sulfate Cs2Ca2(SO4)(3) with a noncentrosymmetric structure was synthesized by high-temperature solid-state reaction, and its crystals were grown by spontaneous crystallization. Single-crystal X-ray diffraction indicates that Cs2Ca2(SO4)(3) features a three-dimensional framework constituted by corner-sharing CaO6 octahedra and SO4 tetrahedra. Optical characterizations suggest that Cs2Ca2(SO4)(3) is transparent down to 200 nm and exhibits a moderate second-order NLO response of about 0.6 x KH2PO4. Electronic band structure calculations were performed to elucidate the optical origin. Furthermore, the title compound has good thermal stability of up to about 1000 K, which is greatly higher than those of NLO sulfates reported recently. This work may shed useful light on the development of new NLO sulfates with high thermal stability.