Lattice dynamics and Mg/Ti order in orthorhombic pseudobrookite-type MgTi2O5

Mg/Ti order/disorder and the lattice dynamics of orthorhombic pseudobrookite-type MgTi2O5 have been studied by experiment and modeling. A mechanochemical activation by high speed ball milling allowed us to synthesize pure MgTi2O5 from MgO and TiO2 anatase at a comparatively low temperature of 1173K. The Mg/Ti order of MgTi2O5 was characterized by X-ray diffraction and Raman spectroscopy. Density functional theory calculations based on fully ordered MgTi2O5 allow an assignment of all experimentally observed Raman and infrared modes and a re-evaluation of earlier findings. A standard entropy of 134.24 Jmol K and a bulk modulus of 161(1)GPa was predicted for fully ordered MgTi2O5 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 B1g(5) Raman blue-shift with the Mg/Ti disorder was observed, which can be used to rapidly quantify the ordering state of MgTi2O5.