The Cubic Field in the System CaO‐ZrO ₂

The range of existence of the cubic phase in the system CaO‐ZrO 2 was determined at temperatures from 1300° to 1700°C, using the lattice parameter method. This technique could not be used at higher temperatures because of anomalous changes in the lattice parameter. The possibility of the existence of a compound, CaZr 4 O 9 , occurring at 20 mole % CaO, was inferred from X‐ray data. The (hypothesized) compound appeared to undergo a phase transformation at about 1650°C. The cubic field was widened when CaCO 2 was substituted for CaO as a reagent, probably because of the formation of an intermediate active oxide. This widening of the field may shed light on some of the discrepancies in the literature.