Phase Equilibria in the System Vanadium Oxide-Niobium Oxide.

Area of Science:

• Materials Science
• Inorganic Chemistry
• Solid-State Chemistry

Background:

• Understanding phase diagrams is crucial for predicting material behavior and developing new compounds.
• The V₂O₅-Nb₂O₅ system is of interest due to the potential for novel material properties.
• Previous studies may have incompletely characterized the high Nb₂O₅ regions of related binary systems.

Purpose of the Study:

• To construct the phase diagram for the pseudo-binary V₂O₅-Nb₂O₅ system.
• To identify and characterize compounds formed within this system.
• To reinvestigate Nb₂O₅-rich portions of binary systems involving Nb₂O₅.

Main Methods:

• Phase diagram construction using fusion characteristics.
• X-ray diffraction analysis to identify crystalline phases.
• Reinvestigation of binary systems: ZnO-Nb₂O₅, NiO-Nb₂O₅, Al₂O₃-Nb₂O₅, TiO₂-Nb₂O₅, and ZrO₂-Nb₂O₅.

Main Results:

• Three compounds were identified in the V₂O₅-Nb₂O₅ system: VNb₉O₂₅, V₂Nb₂₃O₆₂, and a third compound near 93-94 mol% Nb₂O₅.
• VNb₉O₂₅ and V₂Nb₂₃O₆₂ melt incongruently at approximately 1290°C and 1322°C, respectively.
• Nb₂O₅ forms a solid solution with up to 5 mol% V₂O₅, but V₂O₅ does not form a significant solid solution with Nb₂O₅.
• Reinvestigation of other binary systems revealed that previously reported Nb₂O₅ solid solutions contained discrete compounds related to those in the V₂O₅-Nb₂O₅ system.

Conclusions:

• The V₂O₅-Nb₂O₅ phase diagram reveals the formation of specific compounds and limited solid solubility.
• The findings clarify the composition and behavior of Nb₂O₅-rich solid solutions in related binary systems.
• This research provides foundational data for the development of materials based on the V₂O₅-Nb₂O₅ system.