Electronic and structural properties of Y₆Pt₁₃X₄, site occupancy variants of the Ba₆Na₁₆N subnitride (X = Al, Ga)

The existence of new ternary compounds Y₆Pt₁₃X₄ (X = Al, Ga) with the site occupancy variant of the subnitride Ba₆Na₁₆N (space group Im3̄m, no. 229) has been established for the first time by single crystal and powder X-ray diffraction from alloys annealed at 600 °C. The striking structural units in these compounds are platinum centered [PtY₆] octahedra interconnected via Y-Y bonds and embedded in the XPt₃ framework. The structural similarities with the Ce₃Ni₆Si₂-type compounds are discussed. Electronic density of states calculated in the framework of DFT claims the compounds to be metals. The electronic band structures of both compounds resemble each other due to intrinsic similarities in the crystal structures. The analysis of bonding within and between structural fragments based on evaluation of electronic structures, Bader charges and ELF distributions in Y₆Pt₁₃X₄ (X = Al, Ga) suggests the overall picture of these phases as polar intermetallics, containing a mixture of electrostatically driven interactions (such as those between complementary charged yttrium and platinum) and metallic bonding (such as Pt-Al (Ga), Pt-Pt and Y-Al (Ga)).