Natural Mg 2TiO 4 was discovered in the Kangerdlugssuaq region of East Greenland 6 and named qandilite after the Qandil Group of metamorphic rocks at Qala-Dizeh region of Iraq 7. In addition, Mg 2TiO 4 spinel can form a high-temperature superconducting epitaxial thin film 3, 4, and is a good candidate for thin film phosphor in optoelectronic applications due to its red emission at high temperature 5. Mg 2TiO 4 (qandilite) is an oxospinel with excellent dielectric properties that are widely used in satellite communications, mobile phones and wireless communication systems 1, 2. Based on the radii ratio of spinel cations, a simple model is proposed to predict post-spinel structures. The calculated thermal Grüneisen parameters (γ th) of cubic and tetragonal Mg 2TiO 4 phases are 1.01 and 0.63. ![]() The isothermal bulk modulus of the high-pressure tetragonal phase is calculated to be 209(2) GPa and V 0 = 270(2) Å 3 when K T0’ is fixed at 4, and the volume reduction on change from cubic to tetragonal phase is about 9%. The obtained isothermal bulk modulus of Mg 2TiO 4 spinel is K T0 = 148(3) GPa when K T0’ = 6.6, or K T0 = 166(1) GPa when K T0’ is fixed at 4. In the X-ray diffraction experiment, transformation of the cubic Mg 2TiO 4 to the tetragonal structure was complete by 29.2 GPa, ~5 GPa higher than the transition pressure obtained by Raman measurements, owing to slow kinetics. ![]() Owing to sluggish kinetics at room temperature, the spinel phase coexists with the tetragonal phase between 14.7 and 24.3 GPa. The Raman measurements showed that cubic Mg 2TiO 4 spinel transforms to a high pressure tetragonal (I4 1/amd, No.141) phase at 14.7 GPa. Synthetic Mg 2TiO 4 qandilite was investigated to 50 and 40.4 GPa at room temperature using Raman spectroscopy and X-ray diffraction, respectively.
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