Non-stoichiometric La(1 – x)NiO(3 – δ) perovskites produced by combustion synthesis

Abstract

La _{(1 – x)} NiO _{(3 – δ)} perovskites present high metallic conductivity and Pauli-paramagnetism, and could be used as electrodes in electrochemical devices such as SOFCs, PEMFCs and MCFCs. Additionally, due to its σ* conducting band, this material shows a very high electrocatalytic activity, particularly in oxygen reduction processes, with an efficiency comparable to that of platinum. This work describes the combustion synthesis of La _{(1 – x)} NiO _{(3 – δ)} perovskite powders (x = 0 and 0.1) from mixtures of La(NO ₃ ) ₃ ·6H ₂ O and Ni(NO ₃ ) ₂ ·6H ₂ O as cation precursors, and urea as fuel. The as-prepared combustion product, characterized by XRD, DTA/TG, SEM/TEM, BET and dilatometry (after compaction), shows a much higher specific surface area than powders obtained via alternative routes and contains La ₂ NiO ₄ with a typical K ₂ NiF ₄ -type structure, together with small amounts of NiO. The usual subsequent heat treatments for 1 to 12 h at successively higher temperatures showed that full conversion to La _{(1 – x)} NiO _{(3 – δ)} can be readily achieved in air at 750 °C and that the perovskite, after the 12 h heat treatment, remains stable up to 1100 °C. These results show that the combustion technique is a better and much simpler route to the synthesis of perovskite powders.