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(NO₃)₃·6H₂O and Ni(NO₃)₂·6H₂O 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 La₂NiO₄ with a typical K₂NiF₄-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.

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