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-8TiO(2)-0.2MgO and a small amount of Na2O. An interesting crystal structure has been discovered, namely the pseudo-on e-dimensional periodic domain boundary structure with the average periodic value of M = 3.3. The domains show layered structures consisting of corruga ted layers of Ti(Mg)O-6 octahedra, which could be either Cs-x(Ti2-x/2Mgx/2) O-4-type or K-x(Ti2-x/2Mgx/2) O-4-type orthorhombie crystal structure by d ifferent lattice displacement. These two phases employ disordered intergrow th rather than ordered intergrowth like in Na2Ti7O15 which has a periodicit y of 3 + 4 = 7. Coherent domain boundaries were formed neglecting the cryst al structures of domains. The formation of this periodic structure is belie ved to be related to the presence of a small amount of Mg and Na in the sta rting powders. Moreover, the accommodation of small Na cations caused the t ransformation of the crystal structure to be monoclinic with the space grou p P2/m. (C) 2001 Academic Press.