New cubic superstructure of titanium monoxide with double structure imperfection

A cubic model of Ti5O5 (Ti5■O5□=Ti90■18O90□18) superstructure of nonstoichiometric titanium monoxide TixOz with double structure imperfection is proposed for the first time on the basis of symmetry analysis. The unit cell of the cubic superstructure Ti5O5 has a triple lattice constant as compared with that of the basic disordered B1 structure of TixOz monoxide and belongs to the space group Pm3¯m with regard to symmetry. The disorder–order TixOz (space group Fm3¯m)—Ti5O5 (space group Pm3¯m) phase transition channel includes 75 superstructure vectors of seven stars {k10}, {k7}, {k6(1)}, {k6(2)}, {k4(1)}, {k4(2)}, and {k1}. The distribution functions of Ti and O atoms on the sites of the model cubic superstructure Ti5O5 were calculated. Diffraction investigation of annealed ordered titanium monoxide TiO1.087 confirms the existence of the cubic (space group Pm3¯m) ordered phase Ti5O5. The cubic (space group Pm3¯m) superstructure Ti5O5 is shown to be a high-temperature structure with respect to the known monoclinic (space group C2/m) superstructure of the same type.

A cubic (space group Pm3m) model of new Ti5O5 (Ti5■O5□=Ti90■18O90□18) ordered phase of nonstoichiometric titanium monoxide TixOz with double structure imperfection.Figure optionsDownload as PowerPoint slideHighlights
► Cubic model of Ti5O5 (Ti5■O5□=Ti90■18O90□18) superstructure.
► The disorder–order TixOz (space group Fm3¯m)—Ti5O5 (space group Pm3¯m) phase transition channel.
► Distribution of Ti and O atoms and vacancies ■ and □ in the unit cell of cubic Ti5O5 ordered phase.
► Admissible sequences of transformaions connected with the formation of cubic and monoclinic Ti5O5 ordered phases.