Precursor Routes to Complex Ternary Intermetallics: Single-Crystal and Microcrystalline Preparation of Clathrate‑I Na₈Al₈Si₃₈ from NaSi + NaAlSi

Single crystals of the ternary clathrate-I
Na8Al8Si38 were synthesized by kinetically
controlled thermal decomposition (KCTD), and microcrystalline Na8Al8Si38 was synthesized by spark plasma
sintering (SPS) using a NaSi + NaAlSi mixture as the precursor. Na8AlxSi46–x compositions with x ≤ 8 were also
synthesized by SPS from precursor mixtures of different ratios. The
crystal structure of Na8Al8Si38 was
investigated using both Rietveld and single-crystal refinements. Temperature-dependent
transport and UV/vis measurements were employed in the characterization
of Na8Al8Si38, with diffuse-reflectance
measurement indicating an indirect optical gap of 0.64 eV. Our results
indicate that, when more than one precursor is used, both SPS and
KCTD are effective methods for the synthesis of multinary inorganic
phases that are not easily accessible by traditional solid-state synthesis
or crystal growth techniques.