A phase width for CaGaSn. Crystal structure of mixed intermetallic Ca4Ga4+xSn4−x and SmGaxSn3−x, stability, geometry and electronic structure

Abstract

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 Ca4Ga4.9Sn3.1 (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, Ca4Ga4.9Sn3.1 should be considered as a particular composition of Ca4Ga4+xSn4−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.