Effect of cation ordering on the electronic and lattice dynamic properties of Ag2CdGeS4 polytypes: First-principle calculation

The electronic and lattice dynamic properties of I2–II–IV–VI4 quaternary diamond-like semiconductors have a tight connection with their application in the area of solar cell absorption, thermoelectric conversion and so on. Structural configuration of these compounds is focused in present study, although previous researches always pay close attention to compositional modulation. In this paper, Ag2CdGeS4 polytypes (two types of Pna21, one type of Pmn21) have chosen as the representation to establish the relationship between cation ordering and physiochemical properties based on first-principle theory. The results show that cation arrangement practically affects their electronic and lattice dynamic properties such as bonding strength, band structure as well as their infrared spectrum. Due to different cation arrangement, two types (named model S and model P) of the same space group Pna21 demonstrate different properties. For both model P and Pmn21 of different space group, their related properties are alike because of similar cation arrangement. With the resulting cationic Born effective charges, the origin of the difference in electronic properties for three types of Ag2CdGeS4 can be reasonably explained from the viewpoint of vibrational polarization.

First-principle calculations were used to investigate the effect of cation ordering on the electronic and lattice dynamic properties of Ag2CdGeS4 polytypes.Figure optionsDownload as PowerPoint slideHighlights
► Structural configuration was focused other than compositional modulation.
► Establish the relationship between cation ordering and physicochemical properties.
► Explain the reason of different band gap with Born effective charges.
► Calculated infrared spectrum can be used to distinguish different polytypes.