The O−Ti (Oxygen-Titanium) system

This assessment of the Ti--O system covers the phase equilibria and crystal structures of the condensed phases in the composition range between pure Ti and TiO sub 2 . The thermodynamic properties of the Ti oxides have been studied and assessed extensively. The assessed Ti--O phase diagram is shown and its important features have been summarized. The temperature range in which a reasonable equilibrium diagram can be constructed excludes some phase transitions of the higher oxides, and it has not been possible to include all of the observed higher oxide phases in a diagram. However, tables contain complete listings of the phases and phase transitions. Oxygen has a large solubility in low-temperature cph ( alpha Ti), and it stabilizes ( alpha Ti) with respect to the high-temperature bcc form, ( beta Ti). Structures of the monoxides are based on the NaCl structure of the high-temperature gamma TiO form. Four additional structural modifications were identified, which here are designated beta TiO, alpha TiO, beta Ti sub 1--x O, and alpha Ti sub 1--x O. Between the monoxides and TiO sub 2 is a series of discrete phases with stoichiometry Ti sub n O sub 2n--1 , where n = > 2, which are called Magneli phases. It was suggested that discrete equilibrium phases exist for n < = 99. Ti sub n2 O sub 2n--1 (4 < = n < = 10) phases have crystal structures derived from the rutile structure by crystallographic shear. 138 ref.--AA