On the ordering in new low gap semiconductors: PtSnS, PtSnSe, PtSnTe. Experimental and DFT studies

The crystallographic and electronic structures of PtSnS, PtSnSe and PtSnTe were investigated by X-ray structure analysis and density functional theory (DFT) calculations. Conductivity measurements and diffraction patterns show semiconducting ordered pyrite type related compounds containing SnX (X=S, Se, Te) entities. A scheme is presented to model ordered variants according to the relative orientation of the XY dumbbells. It represents the ullmannite, the cobaltite and a new rhombohedral structure type. The scheme allows for a systematic investigation of ordering preferences from first principles. According to the total electronic energy PtSnTe and PtSnSe prefer the cobaltite, PtSnS the rhombohedral structure type. The structural and electronic properties agree with experimental results. The three compounds are predicted to be narrow gap indirect semiconductors from conductivity measurements and band structure calculations.