Synthesis of [NZP]-structure-type materials by the combustion reaction method

Ca_0.5Sr_0.5Zr₄P₆O₂₄ and Ba_1.25Zr₄P_5.5Si_0.5O₂₄ compositions, which belong to the [NZP] family of low-thermal-expansion materials, were synthesized by the combustion reaction method using urea as a fuel and NH₄NO₃ as an oxidizer. The combustion method is a highly exothermic reaction often referred to as self-propagating high-temperature synthesis. The raw materials used were metal zirconates and fine ZrO₂ powders. An earlier-described combustion method using metal nitrates, zirconium oxynitrate, and ammonium dihydrophosphate to synthesize [NZP] compounds was modified in the present study by replacing these costly raw materials with less-expensive oxides. The reactivity of different combinations of raw materials also is discussed.