Supertetrahedral anions in the phosphidosilicates Na1.25Ba0.875Si3P5 and Na31Ba5Si52P83

Solid ionic conductors are one key component of all-solid-state batteries, and recent studies with lithium, sodium and potassium phosphidosilicates revealed remarkable ion conduction capabilities in these compounds. We report the synthesis and crystal structures of two quaternary phosphidosilicates with sodium and barium, which crystallize in new structure types. Na1.25Ba0.875Si3P5 contains layers of T3 supertetrahedra, while Na31Ba5Si52P83 forms defect T5 entities and contains Si-Si bonds and P-3 trimers. Though T-1-relaxometry data indicate a relatively low activation energy for Na+ migration of 0.16 eV, the crystal structures lack sufficient three-dimensional migration paths necessary for fast sodium ion conductvity.

Automated summary

Recent studies have shown that quaternary phosphidosilicates with sodium and barium exhibit remarkable ion conduction capabilities, but the crystal structures may lack sufficient pathways for fast sodium ion conductivity.