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.