Preparation of CuZr₂P₃O₁₂ from alkoxide-derived gels: phase formation as a function of heat treatment

Abstract

The phase formation in alkoxide gels with composition corresponding to CuZr₂P₃O₁₂ has been studied as a function of gel preparation and heat treatment. Two preparational methods have been examined. The chemicals used include Cu(NO)₃ · 3H₂O, Zr(n-OC₃H₇)₄ and either P₂O₅ or H₃PO₄, respectively. The P₂O₅ method results in the formation of di-phase gels. Heat treatment of these invariably gives multi-phase materials. Gels prepared by the H₃PO₄ method are completely amorphous and can be converted into porous glasses by heating to 500 °C. Calcination in the range 650 to 750 ° C results in the formation of a new CuZr₄P₆O₂₄ phase ($\left( {{\text{R}}\bar 3{\text{c,}} a = 1.762_{2 \pm 5} {\text{nm,}} b = 4.39_{9 \pm 1} {\text{nm}}} \right)$. Later, this prevents formation of mono-phase materials during heating to 1200 ° C. It is suggested that this behaviour is related to mixing of Cu²⁺ and Zr⁴⁺ in the normal copper and zirconium positions in the low-temperature${\text{R}}\bar 3{\text{c}} {\text{Cu}}^{{\text{2 + }}}$-Nasicon. Calcination in the range 750 to 850 ° C results in the formation of the normal C2/c Cu²⁺-Nasicon which readily converts to mono-phase Cu⁺-Nasicon (CuZr₂P₃O₁₂) above 880 ° C. Only gels calcined in the range 750 to 850 ° C are useful for the fabrication of mono-phase CuZr₂P₃O₁₂ ceramics.