Optical Properties and Thermal Stability of a Cubic Sulfate Rb_2Ca_2(SO_4)_3

In this paper,a non-centrosymmetric compound of Rb_2Ca_2(SO_4)_3 has been synthesized by a high temperature solid-state reaction and high temperature melting method.Single-crystal X-ray diffraction analysis shows that Rb_2Ca_2(SO_4)_3 crystallizes in the cubic space group of P2_13,and its cell parameters are a=b=c=10.5569(6)?,Z=4 and V=1176.55(12)?~3,respectively.In the crystal structure,SO_4 tetrahedra and Ca O_6 octahedra are connected with each other by a corner-sharing mode to construct the three-dimensional framework of Rb_2Ca_2(SO_4)_3.Optical measurements show that the title compound has a short ultraviolet absorption edge and a moderate second-harmonic generation response.The optical origin is illustrated by the electron band structure calculation.In addition,thermal stability is also studied by virtue of differential thermal/thermogravimetric analysis and powder XRD technique.