Design of a New Family of Inorganic Compounds Ae₂F₂SnX₃ (Ae = Sr, Ba; X = S, Se) Using Rock Salt and Fluorite 2D Building Blocks

We could predict the structure of a new family of compounds Ae2F2SnX3 (Ae = Sr, Ba; X = S, Se) from the stacking of known 2D building blocks of the rock salt and fluorite types. With a high-temperature ceramic method we have then succeeded to synthesize the four compounds Ba2F2SnS3, Ba2F2SnSe3, Sr2F2SnS3, and Sr2F2SnSe3. The structure refinements from X-ray powder diffraction patterns have confirmed the structure predictions and showed their good accuracy. The structure of the four compounds results from the alternated stacking of fluorite [Ae2F2] (Ae = Sr, Ba) and distorted rock salt [SnX3] (X = S, Se) 2D building blocks. As shown by band structure calculations, these blocks behave as a charge reservoir and a charge acceptor, respectively. Sr2F2SnS3 and Ba2F2SnS3 are transparent with optical gaps of 3.06 and 3.21 eV, respectively. However, an attempt to obtain a transparent conductor by substituting Ba per La in Ba2F2SnS3 was unsuccessful.