The Binary System CaO–Nb 2 O 5

The binary system CaO‐Nb 2 O 5 has been shown to include three compounds: CaO·Nb 2 O 5 , which melts congruently at 1560°C; 2CaO·Nb 2 O 5 , which melts congruently at 1576°C; and 3CaO·‐Nb 2 O 5 , which melts incongruently at 1560°C. Three eutectic compositions occur at 6% CaO (1362°C), 23% CaO (1492°C), and 34% CaO (1535°C). These results were obtained by the cone‐fusion technique. The compound 3CaO‐Nb 2 O 5 has been shown to exist in two forms: type I, face‐centered cubic with a = 7.978 A, having a superlattice with a = 23.934 A, and type II, orthorhombic (pseudotetragonal, distorted cubic) with a = 11.51 A, b = 11.10 A, c = 15.98 A, having a pseudocell with a = 5.754 A, b = 5.551 A, and c = 7.990 A. The conditions controlling the formation of these two forms were not determinable from the experiments conducted.