Phase Equilibria in the System Niobium Pentoxide-Germanium Dioxide.

The phase equilibrium diagram for the system Nb2O5-GeO2 has been determined experimentally, using the quenching technique and examining the samples by optical microscopy and x-ray powder diffractometry. The system contains one compound, 9Nb2O5·GeO2, which melts incongruently at 1420 °C. A eutectic between this compound and GeO2 is located at about 97 mol percent GeO2 and 1090 °C. The system does not show liquid immiscibility, and it is concluded that the ionic field strength limit for two-liquid separation in the series of glass formers occurs with the Nb+5 cation.