New quaternary selenoantimonates AHgSbSe_3 (A = Rb, Cs): synthesis, structures and optical properties

摘要

Solvothermal reactions in ethylenediamine have resulted in two quaternary mercury containing selenoantimonates: RbHgSbSe_3 (I) and CsHgSbSe_3 (II). Compound I crystallizes in monoclinc system, space group P2_1/c (no. 14) with a=7.758(2)A, b = 11.234(2)A, c=8.849(2) A, #beta#=106.60(3)deg, V = 739.1(3)A, Z = 4. Compound II crystallizes in orthorhombic system, space group Cmcm (no. 63) with a =4.444(1)A, b = 15.514(6)A, c= 11.261(7)A, V = 776.4(6) A, Z = 4. Both compounds are layered materials and their crystal structures are closely related. Both contain layers of _#infinity#~2[HgSbSe_3] separated by alkali-metal cations A~+ (Rb, Cs). Diffuse reflectance experiments show that both compounds are semiconductors with estimated band gaps of 1.7 eV for I and 1.6 eV for II, respectively.