Lattice dynamics and Mg/Ti order in orthorhombic pseudobrookite-type MgTi2 O5

Mg/Ti order/disorder and the lattice dynamics of orthorhombic pseudobrookite-type MgTi 2 O 5 have been studied by experiment and modeling. A mechanochemical activation by high speed ball milling allowed us to synthesize pure MgTi 2 O 5 from MgO and TiO 2 anatase at a comparatively low temperature of 1173 K. The Mg/Ti order of MgTi 2 O 5 was characterized by X-ray diffraction and Raman spectroscopy. Density functional theory calculations based on fully ordered MgTi 2 O 5 allow an assignment of all experimentally observed Raman and infrared modes and a re-evaluation of earlier findings. A standard entropy of 134.24 J mol −1 K −1 and a bulk modulus of 161(1) GPa was predicted for fully ordered MgTi 2 O 5 and is in good agreement with experimental findings based on quasi-adiabatic calorimetry of samples with different Mg/Ti ordering states and earlier high pressure studies, respectively. A linear relation of the B 1 g (5) Raman blue-shift with the Mg/Ti disorder was observed, which can be used to rapidly quantify the ordering state of MgTi 2 O 5 .