Preparation and characterization of dense sodium superionic conducting Na₅YSi₄O₁₂ (NYS)

Na5YSi4O12 has been prepared from spray-frozen/freeze-dried precursor powders calcined at 620°C for three hours. Sintering at 1140°C for 30 minutes gave a ceramic of 97.7% theoretical density. The material was single phase NYS with a 300°C resistivity of 6.5 Ωcm, an activation energy for Na+ ion conduction of 20.1 kJ/mol, a flexural strength of 75 MPa, a duplex fine grain structure of (0.1–3μm) and a constant linear thermal expansion coefficient (25–470°C) of 13.1 × 10−6/°C ±5%. The properties of the NYS ceramics are especially sensitive to small soda deficiencies.