Synthesis and Characterization of Nano-LaFeO3 Powders by a Softchemistry Method and Corresponding Ceramics

Abstract

The preparation of a nano-sized LaFeO3 powder by a soft-chemistry method usingstarch as complexing agent is described herein. Phase evolution and development of thespecific surface area during the decomposition process of (LaFe)-gels were monitored up to1000 °C. A phase-pure nano-sized LaFeO3 powder with a high specific surface area of 25.7m2/g and a crystallite size of 37 nm was obtained after calcining at 570 °C. TEMinvestigations reveal a porous powder with particles in the range of 20 to 60 nm. Calcinationsto 1000 °C result in crystallite sizes up to 166 nm. Dilatometric measurements of the sinteringbehaviour show that the beginning of shrinkage of pellets from the nano-sized powder is downshifted by more than 300 °C compared to coarse-grained mixed-oxide powder. The orthorhombic - rhombohedral phase transition was observed at 980 °C in DTAmeasurements for coarse-grained ceramic bodies. The enthalpy change (dH) during the phasetransition and the thermal expansion coefficient (adil) for ceramics was determined as 410 J/mol and 11.8×10-6 K-1, respectively. Whereas the enthalpy changes during the phase transition of the nano-sized LaFeO3 powders are £ 200 J/mol.