The system niobium pentoxide-phosphorus pentoxide
1970; Elsevier BV; Volume: 2; Issue: 2 Linguagem: Inglês
10.1016/0022-4596(70)90077-0
ISSN1095-726X
Autores Tópico(s)Thermal and Kinetic Analysis
ResumoA partial phase diagram of the system Nb2O5P2O5 has been determined experimentally, using the quenching technique and identifying the phases by X-ray powder diffractometry. The major phase, NbPO5, has a melting point above 1650°C. It transforms at about 1253°C from a low-temperature, tetragonal phase to a high-temperature, monoclinic phase, isostructural with TaPO5. The 9Nb2O5·P2O5 phase shows a limited solid solution range and melts incongruently at 1435°C. The eutectic between 9:1 and NbPO5 is at 1365°C and 67 mole % Nb2O5. At 96.4 mole % Nb2O5 another phase was found, stable between ∼1340 and 1420°C and isostructural with the 9:1 phase. A new monoclinic phase, "22:1" ss was found, with a limited stability field in both temperature and composition. It is most likely composed of 3 × 3 and 3 × 4 ReO6-type blocks of octahedrally oxygen-coordinated niobium. In the subsystem NbPO5P2O5 liquidus values could not be determined even in sealed Pt tubes because of reactivity and high vapor pressure of P2O5. One compound was identified of probable composition Nb2O5·2P2O5, with pseudocubic symmetry and melting incongruently at about 1025°C. X-ray powder diffraction data and unit cell dimensions are listed for the phases.
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