Sintering of LaFeO₃ Ceramics

Abstract

The sintering of LaFeO 3 has been studied in the temperature interval 1100 -1600°C in air. The effect of cation nonstoichiometry on densification, microstructure, and phase composition is emphasized. La 2 O 3 was observed to inhibit both sintering and grain growth. In Fe-excess materials, exaggerated grain growth occurred, particularly above 1430°C, where a liquid phase was formed. Postsintering swelling was observed in Fe-excess materials above 1430°C. The swelling mechanism is related to phase equilibria, which are reductive in nature and lead to the evolution of oxygen gas. The density in La-excess materials remains high up to 1600°C, but the ceramics might disintegrate in air.

Sintering behaviour of La1−xSrxFeO3−δ mixed conductors

“…Extreme expansion during sintering has also been reported for other related perovskites by the present group 9,11 and others groups. 10,12 It is worth noting that swelling is also observed in ceramics of high-T c superconductors [19][20] where the valence state of Cu is reduced during sintering.…”

“…This is also consistent with dilatometric studies of pure LaFeO 3 and SrFeO 3−δ powders. [9][10][11] The initial sintering temperature is increasing going from pure LaFeO 3 and SrFeO 3−δ , reflecting the difference in the melting temperature of the two pure compounds. So far it has not been possible to determine if the solid state sintering is governed by cation diffusion along grain boundaries or by bulk diffusion.…”

“…La 2 O 3 was observed to be hygroscopic and hydroxides were formed in powders made from the sintered materials, as well as in calcined powders. It is worth noting that La 2 O 3 might cause the sintered materials to disintegrate when stored in air as observed for LaFeO 3 ceramics [9].…”

“…Sintering of LaFeO 3 powders has shown that small amounts of secondary phases in the materials affect the densification behaviour considerably. 9 The densification behaviour of La 1−x Sr x FeO 3−δ has to our knowledge not been studied extensively, but reports on SrFeO 3−δ ceramics [10][11][12][13] show low densities and swelling at higher temperatures. Kleveland et al 11 have emphasized the importance of good control of the cation stoichiometry to avoid post sintering swelling.…”

Preparation of phase pure, dense fine grained ceramics by conventional and spark plasma sintering of La-substituted BiFeO3 nanoparticles

“…This may be because to prepare high density pellets of LaFeO 3 , it is necessary to heat samples at much higher temperatures. 31 Pellet quality was also tested by Raman spectroscopy for each composition, Fig. 4 …”