Al-Nb-O Ternary Phase Diagram Evaluation

The Al-Nb-O system is of interest for materials in structural ceramic applications, for the oxidation behavior of high-temperature niobium alloys, for anode materials of lithium batteries, and to produce metallic niobium. The system contains three ternary oxides in the quasibinary system Al$_2$O$_3$-Nb$_2$O$_5$: NbAlO$_4$, Nb$_{11}$AlO$_{29}$ and Nb$_{49}$AlO$_{124}$. Metallic Nb is in equilibrium with Al$_2$O$_3$ and refractory composites can be made from this material combination. Oxidation of Nb alloyed with Al and of Nb-Al intermetallics occurs in a multistage process where binary and ternary oxides are formed in the early stages of oxidation. The crystal structures of Nb$_{11}$AlO$_{29}$ and Nb$_{49}$AlO$_{124}$ have tunnel-like diffusion pathways for Li$^+$ ions and are investigated as anode materials.