Reaction mechanisms in the formation of perovskite Pb(Fe_1/2Nb_1/2)O₃ by molten salt synthesis method

Abstract

Reaction mechanisms of Pb(Fe_1/2Nb_1/2)O₃ prepared by the molten salt synthesis method using and equimolar mixture of NaCl and KCl have been investigated in the temperature range from 600[ddot]C to 850[ddot]C. Nearly pure perovskite phase, Pb(Fe_1/2Nb_1/2)O₃ with the pyrochlore Pb₃Nb₄O₁₃(P_{3 N}2) phase less than 3% (as determined by x-ray diffraction) can be prepared at 800[ddot]C for 1 hr. The reaction mechanisms of Pb(Fe_1/2Nb_1/2)_O3 are divided into four steps, namely the formation of 1) Pb₃N₂O₈(P₃N) at close to (600[ddot]C, 2) P₃N₂ and Pb₂Fe₂O₅(P₂F) from the reaction of P₃N and Fe₂O₃ at 600 ∼ 700[ddot]C, 3) PFN from the reaction of P₃N₂ with PbO and Fe₂O₃ at 650 ∼ 700[ddot]C, and 4) PFN from the reaction of P₃N₂ with Pb₂Fe₂O₅(P₂F) and PbO above 700[ddot]C. These results can be explained as the improved distribution and reactivity of Fe₂O₃ and the significant formation of the P₂F phase in the molten salt.

Key Words:

• Pb(Fe_1/2Nb_1/2)O₃
• reaction mechanism
• molten salt
• perovskite
• pyrochlore