Spinel and post-spinel phase assemblages in Zn2TiO4: an experimental and theoretical study

Zhang, Yanyao; Liu, Xi; Shieh, Sean R.; Bao, Xinjian; Xie, Tianqi; Wang, Fei; Zhang, Zhigang; Prescher, Clemens; Prakapenka, Vitali B.

doi:10.1007/s00269-016-0841-6

Cited by 9 publications

(11 citation statements)

References 95 publications

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“…If we compare our GGA result for the Fo-III phase to the GGA result for the Rwd (169.3 GPa; Yu and Wentzcovitch [80]), a much larger difference in the K T values,~10.3%, is found. Similarly comparable K T values of the spinel and the CaTi 2 O 4 -type post-spinel phases with the Zn 2 TiO 4 composition, 162.9(5) versus 171(3) GPa (a 5.0% relative difference; K T = 4; the GGA method), were recently disclosed by Zhang et al [81]. In comparison, Zhang et al [82] found a much large difference of~31.3% in the K T values for the spinel (167.…”

Section: Compression Behavior Of Fo Fo-ii Fo-iii and Fo-iv At 0 Ksupporting

confidence: 76%

A Metastable Fo-III Wedge in Cold Slabs Subducted to the Lower Part of the Mantle Transition Zone: A Hypothesis Based on First-Principles Simulations

Zhang

Liu

et al. 2019

Minerals

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The metastable olivine (Ol) wedge hypothesis assumes that Ol may exist as a metastable phase at the P conditions of the mantle transition zone (MTZ) and even deeper regions due to inhibition of the phase transitions from Ol to wadsleyite and ringwoodite caused by low T in the cold subducting slabs. It is commonly invoked to account for the stagnation of the descending slabs, deep focus earthquakes and other geophysical observations. In the last few years, several new structures with the forsterite (Fo) composition, namely Fo-II, Fo-III and Fo-IV, were either experimentally observed or theoretically predicted at very low T conditions. They may have important impacts on the metastable Ol wedge hypothesis. By performing first-principles calculations, we have systematically examined their crystallographic characteristics, elastic properties and dynamic stabilities from 0 to 100 GPa, and identified the Fo-III phase as the most likely metastable phase to occur in the cold slabs subducted to the depths equivalent to the lower part of the MTZ (below the ~600 km depth) and even the lower mantle. As disclosed by our theoretical simulations, the Fo-III phase is a post-spinel phase (space group Cmc21), has all cations in sixfold coordination at P < ~60 GPa, and shows dynamic stability for the entire P range from 0 to 100 GPa. Further, our static enthalpy calculations have suggested that the Fo-III phase may directly form from the Fo material at ~22 GPa (0 K), and our high-T phase relation calculations have located the Fo/Fo-III phase boundary at ~23.75 GPa (room T) with an averaged Clapeyron slope of ~−1.1 MPa/K for the T interval from 300 to 1800 K. All these calculated phase transition pressures are likely overestimated by ~3 GPa because of the GGA method used in this study. The discrepancy between our predicted phase transition P and the experimental observation (~58 GPa at 300 K) can be explained by slow reaction rate and short experimental durations. Taking into account the P-T conditions in the cold downgoing slabs, we therefore propose that the Fo-III phase, rather than the Ol, highly possibly occurs as the metastable phase in the cold slabs subducted to the P conditions of the lower part of the MTZ (below the ~600 km depth) and even the lower mantle. In addition, our calculation has showed that the Fo-III phase has higher bulk seismic velocity, and thus may make important contributions to the high seismic speeds observed in the cold slabs stagnated near the upper mantle-lower mantle boundary. Future seismic studies may discriminate the effects of the Fo-III phase and the low T. Surprisingly, the Fo-III phase will speed up, rather than slow down, the subducting process of the cold slabs, if it metastably forms from the Ol. In general, the Fo-III phase has a higher density than the warm MTZ, but has a lower density than the lower mantle, as suggested by our calculations.

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Section: Compression Behavior Of Fo Fo-ii Fo-iii and Fo-iv At 0 Ksupporting

confidence: 76%

A Metastable Fo-III Wedge in Cold Slabs Subducted to the Lower Part of the Mantle Transition Zone: A Hypothesis Based on First-Principles Simulations

Zhang

Liu

et al. 2019

Minerals

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“…In order to confirm the stability of spinel Zn 2 TiO 4 and the precision of our calculations, the lattice parameters, cell volumes, bulk modulus and pressure derivative of the bulk modulus under zero pressure are given in Table 1, together with the available experimental data and our calculations results for comparison. The optimized unit-cell parameters of spinel Zn 2 TiO 4 (a = 8.522 Å and V = 618.91 Å3 ) are in excellent agreement with the experimental values (a = 8.472 Å and V = 608.17 Å3 ) [15]. Our results are in good agreement with the experimental data, which demonstrates that our simulation is accurate.…”

Section: Structural Propertiessupporting

confidence: 84%

“…We adopt the experimental lattice parameters of spinel Zn 2 TiO 4 with a = 8.472 Å, and V = 608.17 Å3 , to build the initial crystal structure [15]. In this simulation, the pressure was increased in 1 GPa steps.…”

Section: Methodsmentioning

confidence: 99%

“…a e-mail: xiaolingping1982@163.com provided high-quality information about the compressional behavior and compression mechanism of spinel Zn 2 TiO 4 single crystals up to 24 GPa [15]. These experimental and theoretical works have indicated that under hydrostatic conditions there is no evidence of a structural phase transition up to 20 GPa at room temperature.…”

Section: Introductionmentioning

confidence: 99%

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Electronic and optical properties of spinel Zn2TiO4 under pressure effect: ab initio study

2019

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We performed density functional theory (DFT) studies of the lattice parameters, electronic band structure, and optical constants under pressure up to 20 GPa in order to obtain insight into the electronic and optical properties of spinel Zn2TiO4. The results indicate that the structural parameters such as lattice parameters and cell volume show inverse relation to the pressure and shows smooth decreasing behavior from 0 to 20 GPa. Meanwhile, the pressure dependence of the electronic band structure, density of states and partial density of states of spinel Zn2TiO4 up to 20 GPa were presented. From the detailed analysis of the electrical properties, it is concluded that external pressure might be the key reason to enhance band gap. Moreover, the evolution of the dielectric function, absorption coefficient (α(ω)), reflectivity (R(ω)), and the real part of the refractive index (n(ω)) at high pressure are also presented. According to our work, we found that the optical properties of spinel Zn2TiO4 undergo a blue shift with increasing pressure.

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“…The radius ratio r B /r A of Mg 2 TiO 4 is around 1.19 which is larger than the range of CF phase but very close to Zn 2 TiO 4 with radius ratio r B /r A of 1.22. The post-spinel structure of Zn 2 TiO 4 was suggested to be CT phase 48 with an intermediate tetragonal phase 23 . The radii of cations 49 in tetrahedral and octahedral sites could be a determining factor in the structure of AB 2 O 4 spinel.…”

Section: Spinel Phasementioning

confidence: 99%

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

Wang

Shieh

Withers

et al. 2020

Sci Rep

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Synthetic Mg 2 tio 4 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 Mg 2 tio 4 spinel transforms to a high pressure tetragonal (I4 1 /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 Mg 2 tio 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. The obtained isothermal bulk modulus of Mg 2 tio 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. 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 calculated thermal Grüneisen parameters (γ th) of cubic and tetragonal Mg 2 tio 4 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. Mg 2 TiO 4 (qandilite) is an oxospinel with excellent dielectric properties that are widely used in satellite communications, mobile phones and wireless communication systems 1,2. In addition, Mg 2 TiO 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. Natural Mg 2 TiO 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. At ambient pressure, Mg 2 TiO 4 exhibits as a tetragonal structure below 660 °C but as a cubic structure above 660 °C 8,9. The cubic phase breaks down to MgTiO 3 (geikielite) and MgO (periclase) with increasing pressure 10. Synthetic Mg 2 TiO 4 qandilite has inverse spinel structure T (Mg 2+)°(Mg 2+ , Ti 4+)O 4 9,11,12 , which means that Mg 2+ cations occupy both tetrahedral (T) and octahedral (O) sites, while Ti 4+ cations are present only in octahedral sites. The isothermal bulk modulus of cubic qandilite was reported to be 169 GPa, based on empirical calculations 13 , and 175 GPa in a diamond anvil cell study 14 , whereas the adiabatic bulk modulus of qandilite was determined to be 152 GPa by ultrasonic measurements 15. However, no phase transformation was found in previous studies, even though three major post-spinel structures, namely CaTi 2 O 4 (CT; space group Cmcm), CaMn 2 O 4 (CM; space group Pbcm), and CaFe 2 O 4 (CF; space group Pnma) have been proposed to be stable under high pressure environments 16. Unlike CM and CF structures, most CT phases have not been discovered at room temperature but instead under higher temperatures 17-19. In addition to the orthorhombic structures, a tetragonal structure (space group I4 1 /a...

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Spinel and post-spinel phase assemblages in Zn2TiO4: an experimental and theoretical study

Cited by 9 publications

References 95 publications

A Metastable Fo-III Wedge in Cold Slabs Subducted to the Lower Part of the Mantle Transition Zone: A Hypothesis Based on First-Principles Simulations

A Metastable Fo-III Wedge in Cold Slabs Subducted to the Lower Part of the Mantle Transition Zone: A Hypothesis Based on First-Principles Simulations

Electronic and optical properties of spinel Zn2TiO4 under pressure effect: ab initio study

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

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