Raman and X-ray diffraction study of pressure-induced phase transition in synthetic Mg2TiO4

Ching-Pao Wang; Sean R Shieh; Anthony C Withers; Xi Liu; Dongzhou Zhang; Sergey N Tkachev; Abd-Erraouf Djirar; Tianqi Xie; Justin D Rumney

doi:10.1038/s41598-020-63202-5

Raman and X-ray diffraction study of pressure-induced phase transition in synthetic Mg₂TiO₄

Sci Rep. 2020 Apr 14;10(1):6278. doi: 10.1038/s41598-020-63202-5.

Authors

Ching-Pao Wang¹, Sean R Shieh^{2

3}, Anthony C Withers^{4

5}, Xi Liu^{6

7}, Dongzhou Zhang⁸, Sergey N Tkachev⁹, Abd-Erraouf Djirar⁴, Tianqi Xie⁴, Justin D Rumney⁴

Affiliations

¹ Department of Earth Sciences, University of Western Ontario, London, Ontario, N6A 5B7, Canada. jinbaow@gmail.com.
² Department of Earth Sciences, University of Western Ontario, London, Ontario, N6A 5B7, Canada. sshieh@uwo.ca.
³ Department of Physics and Astronomy, University of Western Ontario, London, Ontario, N6A 5B7, Canada. sshieh@uwo.ca.
⁴ Department of Earth Sciences, University of Western Ontario, London, Ontario, N6A 5B7, Canada.
⁵ Bayerisches Geoinstitut, Universität Bayreuth, Bayreuth, Germany.
⁶ Key Laboratory of Orogenic Belts and Crustal Evolution, MOE, Peking University, Beijing, 100871, China.
⁷ School of Earth and Space Sciences, Peking University, Beijing, 100871, China.
⁸ School of Ocean and Earth Science and Technology, Hawai'i Institute of Geophysics and Planetology, University of Hawaii at Manoa, Honolulu, HI, 96822, United States.
⁹ Center for Advanced Radiation Sources, University of Chicago, Chicago, Illinois, 60637, United States.

Abstract

Synthetic Mg₂TiO₄ qandilite was investigated to 50 and 40.4 GPa at room temperature using Raman spectroscopy and X-ray diffraction, respectively. The Raman measurements showed that cubic Mg₂TiO₄ spinel transforms to a high pressure tetragonal (I4₁/amd, No.141) phase at 14.7 GPa. Owing to sluggish kinetics at room temperature, the spinel phase coexists with the tetragonal phase between 14.7 and 24.3 GPa. In the X-ray diffraction experiment, transformation of the cubic Mg₂TiO₄ 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. The obtained isothermal bulk modulus of Mg₂TiO₄ 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. The isothermal bulk modulus of the high-pressure tetragonal phase is calculated to be 209(2) GPa and V₀ = 270(2) Å³ when K_T0' is fixed at 4, and the volume reduction on change from cubic to tetragonal phase is about 9%. The calculated thermal Grüneisen parameters (γ_th) of cubic and tetragonal Mg₂TiO₄ phases are 1.01 and 0.63. Based on the radii ratio of spinel cations, a simple model is proposed to predict post-spinel structures.