Synthesis, structures and physical properties of new transition metal fluoroselenides Ba3F2MSe3 (M = Zn, Cd)

Two new transition metal fluoroselenides Ba3F2MSe3 (M ​= ​Zn, Cd) have been successfully synthesized by solid-state reaction. Both compounds adopt the same crystal structure with orthorhombic space group Pnma (No. 62), consisting of an infinite corner-sharing [MSe3]4- anion chain separated by [Ba3F2]4+ cationic chain of the fluorite type. Ba3F2ZnSe3 and Ba3F2CdSe3 show paramagnetic behaviors from 1.8 to 300 ​K due to the absence of magnetic transition metals. Their Debye temperatures are 170 ​K and 163 ​K, respectively, determined from the low-temperature specific heat measurements. The diffuse-reflectance spectroscopy measurements reveal that these new compounds are semiconductors with optical band gaps of 1.80 ​eV and 1.69 ​eV for Ba3F2ZnSe3 and Ba3F2CdSe3, which are consistent with the band gaps obtained from the first-principle calculations.