Combustion synthesis and properties of the NASICON family of materials

Abstract

The fine-particle NASICON family of materials, MZr₂P₃O₁₂(where M = Na, K, ½Ca and ¼Zr) and NbZrP₃O₁₂, have been prepared by the combustion of aqueous heterogeneous mixtures of stoichiometric amounts of metal nitrate, zirconyl nitrate, niobium phosphate, diammonium hydrogen phosphate, ammonium perchlorate and carbohydrazide (CH) at 400 °C. The formation of NASICON materials was confirmed by powder X-ray diffraction (XRD), IR, solid-state (³¹P) NMR spectroscopy and thermal expansion coefficient measurements. The combustion-synthesized NASICON powders have an average agglomerate size of 9–13 µm with a specific surface area varying from 8 to 28 m² g^–1. The powders pelletized and sintered in the range 1100–1200 °C for 5 h achieved 95–97% theoretical density and showed fine-grain microstructure. The coefficient of thermal expansion of a sintered compact was measured up to 500 °C and ranged from –1.5 × 10^–6°C^–1 to 1.0 × 10^–6°C^–1 depending on the composition.