Sintering of LaCoO3 based ceramics

The densification, microstructure and phase evolution of near stoichiometri c, Go-excess and Co-deficient perovskite La1-xMxCoO3-sigma (M = Ca, Sr; x = 0, 0.2) powders have been investigated by electron microscopy and powder X -ray diffraction. Sub-micron powders were prepared from nitrate precursors using the glycin-nitrate and the EDTA methods. The sintering temperature wa s observed to decrease with Ca or Sr substitution. Dense materials with gra in size in the order of 3-5 mu m have been obtained at 1200 degrees C for n ear stoichiometric powders. Considerable grain growth was observed at highe r sintering temperatures. The presence of other crystalline phases in addit ion to the perovskite due to Co-excess/-deficiency considerably affects the microstructure and acts as grain growth inhibitors by grain boundary pinni ng. The volume fraction of secondary phases is particularly large in the ca se of Co-deficient LaCoO3 due to the formation of La4Co3O10. In non-stoichi ometric La0.8Ca0.2CoO3, a liquid phase consisting mainly of CaO and CoO was observed at 1400 degrees C causing exaggerated grain growth. Considerable pore coarsening was observed in Co-excess La0.8Ca0.2CoO3 at 1350 degrees C. The present investigation demonstrates the importance of controlling the s toichiometry of LaCoO3 based ceramics in order to obtain dense materials wi th well defined microstructure. (C) 2000 Elsevier Science Ltd. All rights r eserved.