A phase width for CaGaSn. Crystal structure of mixed intermetallic Ca₄Ga_4+xSn_4−x and SmGa_xSn_3−x, stability, geometry and electronic structure

X-ray single-crystal structure has been established for new compositions in intermetallic systems of tin and gallium. Crystals were successfully obtained in alloys prepared from elements. The structure of SmGaSn₂ (cubic Pm3̄m, a=4.5778(8) Å, Z=1, R1=0.012) is described with atomic disorder at all Sn/Ga positions and the structure of Ca₄Ga_4.9Sn_3.1 (hexagonal, P6₃/mmc, a=4.2233(9), c=17.601(7) Å, Z=1, R1=0.062) raises an interesting question about existence of a composition domain for CaGaSn. Finally, Ca₄Ga_4.9Sn_3.1 should be considered as a particular composition of Ca₄Ga_4+xSn_4−x, a compound assumed to exist in the range x ~ 0−1. Partial atomic ordering characterizes the Sn/Ga puckered layers of hexagons whose geometries are analyzed and discussed comparatively with analogous arrangements in AlB₂ related hexagonal compounds. The study is supported by rigid band model and DFT calculations performed for different experimental and hypothetic arrangements. - Graphical abstract: A phase width for Ca₄Ga_4+xSn_4−x belonging to the hexagonal YPtAs structure-type. - Highlights: • Single crystals of mixed tin gallium ternary intermetallics were obtained. • Partial ordering at metal sites and phase width are evidenced for Ca₄Ga_4+xSn_4−x. • Layer deviation to flatness is studied comparatively with related structures. • Geometry and stability analyses based on DFT calculations are provided.