Crystal chemistry and formation mechanism of tetragonal MgTi2O4

Symmetry methods of the theory of second-order phase transitions are used to clarify the structural mechanism of the transition from the cubic ( Fd 3 m ) to the tetragonal ( P 4 1 2 1 2) phase of magnesium titanite. The proposed mechanism is consistent with all experimental structural data reported to date for magnesium titanite. We analyze the crystal-chemical features of the structure of tetragonal MgTi 2 O 4 and infer the presence of metallic pico- and nanostructures: two types of Ti 2 dimers, two types of helices along the twofold and fourfold axes of the tetragonal cell, and two types of infinite one-dimensional chains of titanium ions.