Pseudo-One-Dimensional Periodic Domain Boundary Structures in Alkali Titanium Oxides

Potassium- and sodium-doped titanium (magnesium) oxides have been prepared from the starting powders of K2O–8TiO2–0.2MgO and a small amount of Na2O. An interesting crystal structure has been discovered, namely the pseudo-one-dimensional periodic domain boundary structure with the average periodic value of M=3.3. The domains show layered structures consisting of corrugated layers of Ti(Mg)O6 octahedra, which could be either Csx(Ti2-x/2Mgx/2)O4-type or Kx(Ti2-x/2Mgx/2)O4- type orthorhombic crystal structure by different lattice displacement. These two phases employ disordered intergrowth rather than ordered intergrowth like in Na2Ti7O15 which has a periodicity of 3+4=7. Coherent domain boundaries were formed neglecting the crystal structures of domains. The formation of this periodic structure is believed to be related to the presence of a small amount of Mg and Na in the starting powders. Moreover, the accommodation of small Na cations caused the transformation of the crystal structure to be monoclinic with the space group P2/m.