Synthesis and characterization of nano-LaFeO3 powders by a soft-chemistry method and corresponding ceramics

The preparation of a nano-sized LaFeO3 powder by a soft-chemistry method using starch as complexing agent is described herein. Phase evolution and development of the specific surface area during the decomposition process of (LaFe)-gels were monitored up to 1000 °C. A phase-pure nano-sized LaFeO3 powder with high specific surface area of 25.7 m2/g and a crystallite size of 37 nm was obtained after calcining at 570 °C. TEM investigations reveal a porous powder with particles in the range of 20 to 60 nm. Calcinations to 1000 °C result in crystallite sizes up to 166 nm. The dilatometric measurements of the sintering behaviour show that the beginning of shrinkage of pellets from the nano-sized powder is downshifted by more than 300 °C compared to the coarse-grained mixed-oxide powder. The orthorhombic ⇆ rhombohedral phase transition was observed at 980 °C in DTA measurements for the coarse-grained ceramic bodies. The enthalpy change (ΔH) during the phase transition and the thermal expansion coefficient (αdil) for the ceramics were 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.