LIQUID-PHASE BEHAVIOR IN NONSTOICHIOMETRIC CALCIUM-DOPED LANTHANUM CHROMITES

The sinterability of (La,Ca)CrO3 is analysed by comparing the liquid p hase behaviour in A-site excess and A-site deficient compositions (ref erring to the ABO(3) formula). The analysis shows that a series of A-s ite excess and deficient compositions form distinct liquid phases belo nging to the CaO-Cr2O3 phase system. Although both series experience g rain growth and densification due to the presence of a liquid phase, t he A-site excess compositions exhibit greater shrinkage and sinter to closed porosity, whereas the A-site deficient compositions remain poro us. During the final stages of sintering, surplus liquid from the A-si te excess material exudes to the free-surface forming a layer of unifo rm thickness. By comparison, the liquid in the A-site deficient compos ition segregates to the free-surface forming islands and leaving porou s regions in the bulk matrix. It is concluded that the different liqui d phase compositions in the A-site excess and A-site deficient (La,Ca) CrO3 have dissimilar wetting characteristics during the later stages o f sintering. The A-site deficient liquid forms a premature solid phase , which accounts for the difference in sintering behaviour.