Advanced Search

Indexed by SCI、CA、РЖ、PA、CSA、ZR、etc .

Volume 31 Issue 6
Dec.  2020
Turn off MathJax
Article Contents

Sha Wang, Jinhua Zhang, Joseph R Smyth, Junfeng Zhang, Dan Liu, Xi Zhu, Xiang Wang, Yu Ye. Crystal Structure, Thermal Expansivity and High-Temperature Vibrational Spectra on Natural Hydrous Rutile. Journal of Earth Science, 2020, 31(6): 1190-1199. doi: 10.1007/s12583-020-1351-5
Citation: Sha Wang, Jinhua Zhang, Joseph R Smyth, Junfeng Zhang, Dan Liu, Xi Zhu, Xiang Wang, Yu Ye. Crystal Structure, Thermal Expansivity and High-Temperature Vibrational Spectra on Natural Hydrous Rutile. Journal of Earth Science, 2020, 31(6): 1190-1199. doi: 10.1007/s12583-020-1351-5

Crystal Structure, Thermal Expansivity and High-Temperature Vibrational Spectra on Natural Hydrous Rutile

doi: 10.1007/s12583-020-1351-5
More Information
  • A natural rutle sample was measured by in situ high-temperature X-ray diffraction (XRD) patterns, as well as Raman and Fourier transform infrared (FTIR). Crystal structure is refined on the sample with 1.4 mol.% Fe and 510±120 ppmw. H2O. The unit-cell and TiO6 octahedral volumes are expanded by 0.7%-0.8% for Fe3+ incorporation, as compared with the reported Ti-pure samples. The volumetric thermal expansion coefficient (α, K-1) could be approximated as a linear function of T (K):4.95(3)×10-9×T+21.54(5)×10-6, with the averaged value α0=30.48(5)×10-6 K-1, in the temperature range of 300-1 500 K. The internal Ti-O stretching (A1g and B2g) and O-Ti-O bending (Eg) modes show 'red shift', whereas the multi-phonon process exhibits 'blue shift' at elevated temperature. The rotational mode (B1g) for TiO6 octahedra is nearly insensitive to temperature variations. The OH-stretching bands at 3 279 and 3 297 cm-1 are measured by high-temperature spectroscopy experiments. Both the IR-active and Raman-active OH-stretching modes shift to lower frequencies at higher temperature, with the signal intensities decreasing. And after quenching, we expect about 43% dehydration around 873 K, and 85% dehydration at 1 273 K for this hydrous sample.
  • 加载中
  • Arlt, T., Bermejo, M., Blanco, M. A., et al., 2000. High-Pressure Polymorphs of Anatase TiO2. Physical Review B, 61(21):14414-14419. https://doi.org/10.1103/physrevb.61.14414 doi:  10.1103/physrevb.61.14414
    Balachandran, U., Eror, N. G., 1982. Raman Spectra of Titanium Dioxide. Journal of Solid State Chemistry, 42(3):276-282. https://doi.org/10.1016/0022-4596(82)90006-8 doi:  10.1016/0022-4596(82)90006-8
    Bromiley, G. D., Hilairet, N., 2005. Hydrogen and Minor Element Incorporation in Synthetic Rutile. Mineralogical Magazine, 69(3):345-358. https://doi.org/10.1180/0026461056930256 doi:  10.1180/0026461056930256
    Bromiley, G. D., Shiryaev, A. A., 2006. Neutron Irradiation and Post-Irradiation Annealing of Rutile (TiO2-x):Effect on Hydrogen Incorporation and Optical Absorption. Physics and Chemistry of Minerals, 33(6):426-434. https://doi.org/10.1007/s00269-006-0087-9 doi:  10.1007/s00269-006-0087-9
    Bromiley, G. D., Hilairet, N., Mccammon, C., 2004. Solubility of Hydrogen and Ferric Iron in Rutile and TiO2 (Ⅱ):Implications for Phase Assemblages during Ultrahigh-Pressure Metamorphism and for the Stability of Silica Polymorphs in the Lower Mantle. Geophysical Research Letters, 31(4):L04610. https://doi.org/10.1029/2004gl019430 doi:  10.1029/2004gl019430
    Cao, Y. T., Liu, L., Yang, W. Q., et al., 2019. Reconstruction the Process of Partial Melting of the Retrograde Eclogite from the North Qaidam, Western China:Constraints from Titanite U-Pb Dating and Mineral Chemistry. Journal of Earth Science, 30(6):1166-1177. https://doi.org/10.1007/s12583-019-1253-6 doi:  10.1007/s12583-019-1253-6
    Cromer, D. T., Mann, J. B., 1968. X-Ray Scattering Factors Computed from Numerical Hartree-Fock Wave Functions. Acta Crystallographica Section A, 24(2):321-324. https://doi.org/10.1107/s0567739468000550 doi:  10.1107/s0567739468000550
    Deer, W. A., Howie, R. A., Zussman, J., 1963. An Introduction to the Rock-Forming Minerals. Journal of Geology, 71:534-536. https://doi.org/10.1086/626928 doi:  10.1086/626928
    Dolomanov, O. V., Blake, A. J., Champness, N. R., et al., 2003. OLEX:New Software for Visualization and Analysis of Extended Crystal Structures. Journal of Applied Crystallography, 36(5):1283-1284. https://doi.org/10.1107/s0021889803015267 doi:  10.1107/s0021889803015267
    Downs, R. T., Bartelmehs, K. L., Gibbs, G. V., et al., 1993. Interactive Software for Calculating and Displaying X-Ray or Neutron Powder Diffractometer Patterns of Crystalline Materials. American Mineralogist, 78:1104-1107. https://doi.org/10.1029/93jb01427 doi:  10.1029/93jb01427
    Fei, Y., 1995. Thermal Expansion. In: Ahrens, J. T., ed., Mineral Physics and Crystallography. American Geophysical Union, Washington. 29-44
    Foley, S. F., Barth, M. G., Jenner, G. A., 2000. Rutile/Melt Partition Coefficients for Trace Elements and an Assessment of the Influence of Rutile on the Trace Element Characteristics of Subduction Zone Magmas. Geochimica et Cosmochimica Acta, 64(5):933-938. https://doi.org/10.1016/s0016-7037(99)00355-5 doi:  10.1016/s0016-7037(99)00355-5
    Guo, H. H., 2017. In-situ Infrared Spectra of OH in Rutile up to 1 000 ℃. Physics and Chemistry of Minerals, 44(8):547-552. https://doi.org/10.1007/s00269-017-0881-6 doi:  10.1007/s00269-017-0881-6
    Hammer, V. M. F., Beran, A., 1991. Variations in the OH Concentration of Rutiles from Different Geological Environments. Mineralogy and Petrology, 45(1):1-9. https://doi.org/10.1007/bf01164498 doi:  10.1007/bf01164498
    Hara, Y., Nicol, M., 1979. Raman Spectra and the Structure of Rutile at High Pressures. Physica Status Solidi B, 94(1):317-322. https://doi.org/10.1002/pssb.2220940137 doi:  10.1002/pssb.2220940137
    Hazen, R. M., Finger, L. W., 1981. Bulk Moduli and High-Pressure Crystal Structures of Rutile-Type Compounds. Journal of Physics and Chemistry of Solids, 42(3):143-151. https://doi.org/10.1016/0022-3697(81)90074-3 doi:  10.1016/0022-3697(81)90074-3
    Hemley, R. J., Mao, H. K., Chao, E. C. T., 1986. Raman Spectrum of Natural and Synthetic Stishovite. Physics and Chemistry of Minerals, 13(5):285-290. https://doi.org/10.1007/bf00308345 doi:  10.1007/bf00308345
    Henderson, C. M. B., Knight, K. S., Lennie, A. R., 2009. Temperature Dependence of Rutile (TiO2) and Geikielite (MgTiO3) Structures Determined Using Neutron Powder Diffraction. The Open Mineralogy Journal, 3(1):1-11. https://doi.org/10.2174/1874456700903010001 doi:  10.2174/1874456700903010001
    Holland, T. J. B., Redfern, S. A. T., 1997. Unit Cell Refinement from Powder Diffraction Data:The Use of Regression Diagnostics. Mineralogical Magazine, 61(404):65-77. https://doi.org/10.1180/minmag.1997.061.404.07 doi:  10.1180/minmag.1997.061.404.07
    Howard, C. J., Sabine, T. M., Dickson, F., 1991. Structural and Thermal Parameters for Rutile and Anatase. Acta Crystallographica Section B Structural Science, 47(4):462-468. https://doi.org/10.1107/s010876819100335x doi:  10.1107/s010876819100335x
    Hummer, D. R., Heaney, P. J., Post, J. E., 2007. Thermal Expansion of Anatase and Rutile between 300 and 575 K Using Synchrotron Powder X-Ray Diffraction. Powder Diffraction, 22:352-357. https://doi.org/10.1154/1.2790965 doi:  10.1154/1.2790965
    Isaak, D. G., Carnes, J. D., Anderson, O. L., et al., 1998. Elasticity of TiO2 Rutile to 1 800 K. Physics and Chemistry of Minerals, 26(1):31-43. https://doi.org/10.1007/s002690050158 doi:  10.1007/s002690050158
    Johnson, O. W., Ohlsen, W. D., Kingsbury, P. I., 1968. Defects in Rutile Ⅲ. Optical and Electronic Properties of Impurities and Charge Carriers. Physical Review, 175:1102-1109. https://doi.org/10.1103/physrev.185.1230.2 doi:  10.1103/physrev.185.1230.2
    Johnson, O. W., DeFord, J., Shaner, J. W., 1973. Experimental Technique for the Precise Determination of H and D Concentration in Rutile (TiO2). Journal of Applied Physics, 44(7):3008-3012. https://doi.org/10.1063/1.1662697 doi:  10.1063/1.1662697
    Klemme, S., Blundy, J. D., Wood, B. J., 2002. Experimental Constraints on Major and Trace Element Partitioning during Partial Melting of Eclogite. Geochimica et Cosmochimica Acta, 66(17):3109-3123. https://doi.org/10.1016/s0016-7037(02)00859-1 doi:  10.1016/s0016-7037(02)00859-1
    Koudriachova, M. V., de Leeuw, S. W., Harrison, N. M., 2004. First-Principles Study of H Intercalation in Rutile TiO2. Physical Review B, 70(16):165421. https://doi.org/10.1103/physrevb.70.165421 doi:  10.1103/physrevb.70.165421
    Kumar, M., 1995. High Pressure Equation of State for Solids. Physica B:Condensed Matter, 212(4):391-394. https://doi.org/10.1016/0921-4526(95)00361-c doi:  10.1016/0921-4526(95)00361-c
    Kumar, M., 1996. Application of High Pressure Equation of State for Different Classes of Solids. Physica B:Condensed Matter, 217(1/2):143-148. https://doi.org/10.1016/0921-4526(95)00448-3 doi:  10.1016/0921-4526(95)00448-3
    Kumar, M., 2003. Thermoelastic Properties of Minerals. Physics and Chemistry of Minerals, 30:556-558. https://doi.org/10.1007/s00269-003-0344-0 doi:  10.1007/s00269-003-0344-0
    Lan, T., Tang, X. L., Fultz, B., 2012. Phonon Anharmonicity of Rutile TiO2 Studied by Raman Spectrometry and Molecular Dynamics Simulations. Physical Review B, 85(9):094305. https://doi.org/10.1103/physrevb.85.094305 doi:  10.1103/physrevb.85.094305
    Li, K. Y., Xue, D. F., 2006. Estimation of Electronegativity Values of Elements in Different Valence States. The Journal of Physical Chemistry A, 110(39):11332-11337. https://doi.org/10.1021/jp062886k doi:  10.1021/jp062886k
    Libowitzky, E., 1999. Correlation of O-H Stretching Frequencies and O-H…O Hydrogen Bond Lengths in Minerals. Monatshefte für Chemie, 130(8):1047-1059. https://doi.org/10.1007/bf03354882 doi:  10.1007/bf03354882
    Litasov, K. D., Kagi, H., Shatskiy, A., et al., 2007. High Hydrogen Solubility in Al-Rich Stishovite and Water Transport in the Lower Mantle. Earth and Planetary Science Letters, 262(3/4):620-634. https://doi.org/10.1016/j.epsl.2007.08.015 doi:  10.1016/j.epsl.2007.08.015
    Lucassen, F., Koch-Muller, M., Taran, M., et al., 2012. Coupled H and Nb, Cr, and V Trace Element Behavior in Synthetic Rutile at 600 ℃, 400 MPa and Possible Geological Application. American Mineralogist, 98(1):7-18. https://doi.org/10.2138/am.2013.4183 doi:  10.2138/am.2013.4183
    Maldener, J., Rauch, F., Gavranic, M., et al., 2001. OH Absorption Coefficients of Rutile and Cassiterite Deduced from Nuclear Reaction Analysis and FTIR Spectroscopy. Mineralogy and Petrology, 71(1/2):21-29. https://doi.org/10.1007/s007100170043 doi:  10.1007/s007100170043
    Mammone, J. F., Sharma, S. K., Nicol, M., 1980. Raman Study of Rutile (TiO2) at High Pressures. Solid State Communications, 34(10):799-802. https://doi.org/10.1016/0038-1098(80)91055-8 doi:  10.1016/0038-1098(80)91055-8
    Meagher, E. P., Lager, G. A., 1979. Polyhedral Thermal Expansion in the TiO2 Polymorphs:Refinement of the Crystal Structure of Rutile and Brookite at High Temperature. The Canadian Mineralogist, 17:77-85 http://www.researchgate.net/publication/299160965_Polyhedral_thermal_expansion_in_the_TiO2_polymorphs_Refinement_of_the_crystal_structures_of_rutile_and_brookite_at_high_temperature
    Miao, Y. F., Pang, Y. W., Ye, Y., et al., 2019. Crystal Structures and High-Temperature Vibrational Spectra for Synthetic Boron and Aluminum Doped Hydrous Coesite. Crystals, 9(12):642. https://doi.org/10.3390/cryst9120642 doi:  10.3390/cryst9120642
    Ming, L. C., Manghnani, M. H., 1979. Isothermal Compression of TiO2 (Rutile) under Hydrostatic Pressure to 106 kbar. Journal of Geophysical Research, 84(B9):4777-4779. https://doi.org/10.1029/jb084ib09p04777 doi:  10.1029/jb084ib09p04777
    Mookherjee, M., Redfern, S. A. T., Zhang, M., 2001. Thermal Response of Structure and Hydroxyl Ion of Phengite-2M1:An in situ Neutron Diffraction and FTIR Study. European Journal of Mineralogy, 13(3):545-555. https://doi.org/10.1127/0935-1221/2001/0013-0545 doi:  10.1127/0935-1221/2001/0013-0545
    Nie, J. Z., Liu, Y. C., Yang, Y., 2018. Phase Equilibria Modeling and P-T Evolution of the Mafic Lower-Crustal Xenoliths from the Southeastern Margin of the North China Craton. Journal of Earth Science, 29(5):1236-1253. https://doi.org/10.1007/s12583-018-0849-6 doi:  10.1007/s12583-018-0849-6
    Pawley, A. R., McMillan, P. F., Holloway, J. R., 1993. Hydrogen in Stishovite, with Implications for Mantle Water Content. Science, 261(5124):1024-1026. https://doi.org/10.1126/science.261.5124.1024 doi:  10.1126/science.261.5124.1024
    Porto, S. P. S., Fleury, P. A., Damen, T. C., 1967. Raman Spectra of TiO2, MgF2, ZnF2, FeF2 and MnF2. Physical Review, 154(2):522-526. https://doi.org/10.1103/physrev.154.522 doi:  10.1103/physrev.154.522
    Rao, K. V. K., Naidu, S. V. N., Iyengar, L., 1970. Thermal Expansion of Rutile and Anatase. Journal of the American Ceramic Society, 53(3):124-126. https://doi.org/10.1111/j.1151-2916.1970.tb12051.x doi:  10.1111/j.1151-2916.1970.tb12051.x
    Rossman, G. R., Smyth, J. R., 1990. Hydroxyl Content of Accessory Minerals in Mantle Eclogites and Related Rocks. American Mineralogist, 75:775-780 http://ci.nii.ac.jp/naid/80005531407
    Samara, G. A., Peercy, P. S., 1973. Pressure and Temperature Dependence of the Static Dielectric Constants and Raman Spectra of TiO2 (Rutile). Physical Review B, 7(3):1131-1148. https://doi.org/10.1103/physrevb.7.1131 doi:  10.1103/physrevb.7.1131
    Sato, Y., 1977. Equation of State of Mantle Minerals Determined through High-Pressure X-Day Study. High Pressure Research Applications in Geophysics, (1977):307-323. https://doi.org/10.1016/b978-0-12-468750-9.50028-0 doi:  10.1016/b978-0-12-468750-9.50028-0
    Saxena, S. K., Chatterjee, N., Fei, Y., et al., 1993. Thermodynamic Data on Oxides and Silicates:An Assessed Data Set Based on Thermochemistry and High Pressure Phase Equilibrium. Springer-Verlag, Berlin, Heidelberg, New York
    Sheng, Y. M., Xia, Q. K., Hao, Y. T., 2007. Water in Rutiles from UHP Eclogites in the Dabie Orogen. Acta Petrologica et Mineralogica, 26:269-274 (in Chinese with English Abstract) http://en.cnki.com.cn/Article_en/CJFDTOTAL-YSKW200703009.htm
    Soffer, B. H., 1961. Studies of the Optical and Infrared Absorption Spectra of Rutile Single Crystals. The Journal of Chemical Physics, 35(3):940-945. https://doi.org/10.1063/1.1701242 doi:  10.1063/1.1701242
    Song, Y. R., Jin, Z. M., 2002. Nanometer-Sized UHP Rutile:Tracing the Depth of Continental Deep Subduction. Earth Science Frontiers, 9:267-272 (in Chinese with English Abstract) http://en.cnki.com.cn/Article_en/CJFDTOTAL-DXQY200204008.htm
    Su, W., Li, J. L., Mao, Q., et al., 2018. Rutile in HP Rocks from the Western Tianshan, China:Mineralogy and Its Economic Implications. Journal of Earth Science, 29(5):1049-1059. https://doi.org/10.1007/s12583-018-0848-7 doi:  10.1007/s12583-018-0848-7
    Sugiyama, K., Takéuchi, Y., 1991. The Crystal Structure of Rutile as a Function of Temperature up to 1 600℃. Zeitschrift für Kristallographie-Crystalline Materials, 194(1/2/3/4):305-313. https://doi.org/10.1524/zkri.1991.194.14.305 doi:  10.1524/zkri.1991.194.14.305
    Suzuki, I., 1975. Thermal Expansion of Periclase and Olivine, and Their Anharmonic Properties. Journal of Physics of the Earth, 23(2):145-159. https://doi.org/10.4294/jpe1952.23.145 doi:  10.4294/jpe1952.23.145
    Suzuki, I., Okajima, S. I., Seya, K., 1979. Thermal Expansion of Single-Crystal Manganosite. Journal of Physics of the Earth, 27(1):63-69. https://doi.org/10.4294/jpe1952.27.63 doi:  10.4294/jpe1952.27.63
    Swope, R. J., Smyth, J. R., Larson, A. C., 1995. H in Rutile-Type Compounds:I. Single-Crystal Neutron and X-Ray Diffraction Study of H in Rutile. American Mineralogist, 80(5/6):448-453. https://doi.org/10.2138/am-1995-5-604 doi:  10.2138/am-1995-5-604
    Tokonami, M., 1965. Atomic Scattering Factor for O2-. Acta Crystallographica, 19(3):486-486. https://doi.org/10.1107/s0365110x65003729 doi:  10.1107/s0365110x65003729
    Touloukian, Y. S., Kirby, R. K., 1977. Thermophysical Properties of Matter; Volume 13:Thermal Expansion; Nonmetallic Solids. IFI/Plenum, New York, Washington
    Vlassopoulos, D., Rossman, G. R., Haggerty, S. E., 1993. Coupled Substitution of High and Minor Elements in Rutile and the Implications of High OH Contents in Nb-and Cr-Rich Rutile from the Upper Mantle. American Mineralogist, 78:1181-1191 http://ammin.geoscienceworld.org/content/78/11-12/1181
    Wang, X., Xu, X. X., Ye, Y., et al., 2019. In-situ High-Temperature XRD and FTIR for Calcite, Dolomite and Magnesite:Anharmonic Contribution to the Thermodynamic Properties. Journal of Earth Science, 30(5):964-976. https://doi.org/10.1007/s12583-019-1236-7 doi:  10.1007/s12583-019-1236-7
    Xie, Z. J., Liu, X. W., Jin, Z. M., et al., 2020. Microstructures and Phase Transition in Omphacite:Constraints on the P-T Path of Shuanghe Eclogite (Dabie Orogen). Journal of Earth Science, 31(2):254-261. https://doi.org/10.1007/s12583-019-1279-9 doi:  10.1007/s12583-019-1279-9
    Xiong, X. L., Adam, J., Green, T. H., 2005. Rutile Stability and Rutile/Melt HFSE Partitioning during Partial Melting of Hydrous Basalt:Implications for TTG Genesis. Chemical Geology, 218(3/4):339-359. https://doi.org/10.1016/j.chemgeo.2005.01.014 doi:  10.1016/j.chemgeo.2005.01.014
    Xiong, X. L., Keppler, H., Audétat, A., et al., 2011. Partitioning of Nb and Ta between Rutile and Felsic Melt and the Fractionation of Nb/Ta during Partial Melting of Hydrous Metabasalt. Geochimica et Cosmochimica Acta, 75(7):1673-1692. https://doi.org/10.1016/j.gca.2010.06.039 doi:  10.1016/j.gca.2010.06.039
    Yang, Y., Xia, Q., Feng, M., et al., 2011. In situ FTIR Investigations at Varying Temperatures on Hydrous Components in Rutile. American Mineralogist, 96(11/12):1851-1855. https://doi.org/10.2138/am.2011.3826 doi:  10.2138/am.2011.3826
    Zack, T., Kronz, A., Foley, S. F., et al., 2002. Trace Element Abundances in Rutiles from Eclogites and Associated Garnet Mica Schists. Chemical Geology, 184(1/2):97-122. https://doi.org/10.1016/s0009-2541(01)00357-6 doi:  10.1016/s0009-2541(01)00357-6
    Zaffiro, G., Angel, R. J., Alvaro, M., 2019. Constraints on the Equations of State of Stiff Anisotropic Minerals:Rutile, and the Implications for Rutile Elastic Barometry. Mineralogical Magazine, 83(3):339-347. https://doi.org/10.1180/mgm.2019.24 doi:  10.1180/mgm.2019.24
  • 加载中
通讯作者: 陈斌, bchen63@163.com
  • 1. 

    沈阳化工大学材料科学与工程学院 沈阳 110142

  1. 本站搜索
  2. 百度学术搜索
  3. 万方数据库搜索
  4. CNKI搜索

Figures(10)  / Tables(1)

Article Metrics

Article views(33) PDF downloads(5) Cited by()

Related
Proportional views

Crystal Structure, Thermal Expansivity and High-Temperature Vibrational Spectra on Natural Hydrous Rutile

doi: 10.1007/s12583-020-1351-5

Abstract: A natural rutle sample was measured by in situ high-temperature X-ray diffraction (XRD) patterns, as well as Raman and Fourier transform infrared (FTIR). Crystal structure is refined on the sample with 1.4 mol.% Fe and 510±120 ppmw. H2O. The unit-cell and TiO6 octahedral volumes are expanded by 0.7%-0.8% for Fe3+ incorporation, as compared with the reported Ti-pure samples. The volumetric thermal expansion coefficient (α, K-1) could be approximated as a linear function of T (K):4.95(3)×10-9×T+21.54(5)×10-6, with the averaged value α0=30.48(5)×10-6 K-1, in the temperature range of 300-1 500 K. The internal Ti-O stretching (A1g and B2g) and O-Ti-O bending (Eg) modes show 'red shift', whereas the multi-phonon process exhibits 'blue shift' at elevated temperature. The rotational mode (B1g) for TiO6 octahedra is nearly insensitive to temperature variations. The OH-stretching bands at 3 279 and 3 297 cm-1 are measured by high-temperature spectroscopy experiments. Both the IR-active and Raman-active OH-stretching modes shift to lower frequencies at higher temperature, with the signal intensities decreasing. And after quenching, we expect about 43% dehydration around 873 K, and 85% dehydration at 1 273 K for this hydrous sample.

Sha Wang, Jinhua Zhang, Joseph R Smyth, Junfeng Zhang, Dan Liu, Xi Zhu, Xiang Wang, Yu Ye. Crystal Structure, Thermal Expansivity and High-Temperature Vibrational Spectra on Natural Hydrous Rutile. Journal of Earth Science, 2020, 31(6): 1190-1199. doi: 10.1007/s12583-020-1351-5
Citation: Sha Wang, Jinhua Zhang, Joseph R Smyth, Junfeng Zhang, Dan Liu, Xi Zhu, Xiang Wang, Yu Ye. Crystal Structure, Thermal Expansivity and High-Temperature Vibrational Spectra on Natural Hydrous Rutile. Journal of Earth Science, 2020, 31(6): 1190-1199. doi: 10.1007/s12583-020-1351-5
  • Rutile, TiO2, is an important and common accessory mineral found in metamorphic and igneous rocks, especially in eclogites and kimberlite (Xie et al., 2020; Nie et al., 2018; Zack et al., 2002). In addition, rutile-type titanium dioxide has a variety of high-pressure phases (Su et al., 2018; Song and Jin, 2002). Although rutile has a simple tetragonal structure with each Ti4+ cation coordinated with 6 O2- anions (Bromiley and Hilairet, 2005; Deer et al., 1963), it can incorporate significant amounts of trivalent (Fe3+, Al3+, Cr3+, Mn3+, etc.), pentavalent (such as Nb5+, Ta5+) as well as divalent (Mg2+, Ca2+) cations inside the structure (Cao et al., 2019; Bromiley and Hilaret, 2005; Bromiley et al., 2004; Rossman and Smyth, 1990). In geological and geochemical systems, rutile may serve as a potential controller of the Nb5+, Ta5+ budget in the subduction zone processes (e.g., Xiong et al., 2011, 2005; Klemme et al., 2002; Foley et al., 2000). On the other hand, as one of the important nominally anhydrous minerals (NAMs), rutile can contain hundreds of ppm water (by weight, ppmw.) as hydroxyl defects inside the structure (Sheng et al., 2007; Hammer and Beran, 1991), while Vlassopoulos et al. (1993) reported water concentrations as high as a few thousand ppmw. with the incorporation of Nb5+ and Ta5+ cations in natural rutile samples.

    In order to constrain structural water (i.e., hydrogen defects in the lattice) behavior in the rutile structure, extensive FTIR measurements have been reported on the hydrous rutile samples (e.g., Guo, 2017; Yang et al., 2011; Bromiley and Hilairet, 2005; Bromiley et al., 2004; Hammer and Beran, 1991; Johnson et al., 1973, 1968; Soffer, 1961). A typical OH-stretching mode at 3 279 cm-1 is usually observed in the FTIR spectra, which is associated with the reduction of Ti4+ cation (Ti4+=Ti3++H+) (Bromiley and Shirvaev, 2006), while other OH-stretching bands at different wavenumber positions are coupled with incorporated metallic cations. For example, the band at 3 297 cm-1 is attributed to Fe3+ incorporation (Ti4+=Fe3++H+). The single-crystal structure refinement (Swope et al., 1995) indicated that the most possible site for protonation is slightly displaced away from (1/2, 1/2, 0) in hydrous rutile, which is in accordance with the strong polarization of the IR-active OH-stretching band in the (001) plane.

    On the other hand, the thermo-elasticity and Equations of State (EOSs) for rutile have also been widely studied (e.g., Isaak et al., 1998; Saxena et al., 1993; Hazen and Finger, 1981; Ming and Manghnani, 1979; Sato, 1977; Touloukian and Kirby, 1977). The isothermal bulk modulus of rutile is significantly larger than those for garnet minerals, while their thermal expansion coefficients are similar to each other. Consequently, the rutile inclusions trapped inside garnets in the the metamorphic rocks would show negative residual pressure when measured at room temperature, which is not suitable for elastic geo-barometry (Zaffiro et al., 2019).

    In this study, we measured high-temperature X-ray diffraction patterns, as well as Raman and FTIR spectra on rutile. The thermal expansion coefficient has been well constrained as a function of temperature, since there are quite large discrepancies for the thermal expansivity among the reported studies (Henderson et al., 2009; Hummer et al., 2007; Saxena et al., 1993; Sugiyama and Takéuchi, 1991; Touloukian and Kirby, 1977; Rao et al., 1970). The crystal structure refinement and measurement on the thermal expansivity on this Fe-bearing rutile sample are crucial for understanding Fe effect on the crystal chemistry at high temperatures, as compared with the previous studies on the TiO2-pure ones. This information could be helpful for exploring the metallic cation substitution mechanism in rutile at high temperatures in the lower crust and mantle.

    On the other hand, the lattice vibrations have also been examined in a larger temperature range from 83 to 1 473 K, which may provide useful constraints on the anharmonic properties in rutile (Lan et al., 2012; Samara and Peercy, 1973). The OH-stretching modes were characterized by both Raman and FTIR spectra in a T-range up to 1 273 K, and comparison will be made with the previous FTIR measurements below 773 K (Guo, 2017; Yang et al., 2011). This measurement could provide us important information about the dehydration mechanism in rutile in a wider temperature range, which is relevant to the hydration behavior in rutile at the high-temperature conditions in the mantle.

  • A natural rutile sample from eclogite in Dabie Mountain, Anhui, China, which is homogenous dark brown in color under microscope and in needle shape with longitudinal grain development on the crystal surface, was adopted for this study. A single-crystal chip (200 μm×80 μm×50 μm) from the sample source was selected for the characterization of chemical composition by a JEOL JXA-8100 EPMA, which is operated at an accelerating voltage of 15 kV, a beam current of 5 nA, as well as a spot size of 5 μm, so as to minimize the fluctuations of the X-ray intensity as well as the damage on the sample (Wang et al., 2019). We used the certified mineral standards below for quantification, with ZAF wavelength-dispersive corrections: MnTiO3 (Ti), gallium arsenide (Ga), chromium metal (Cr), wollastonite (Ca), spinel (Al), enstatite (Mg) and hematite (Fe). Eight points in total were measured on different locations of this natural sample piece, and the formula (Table S1) could be expressed as: Ti0.988Fe0.014Ga0.000 6Al0.000 8Cr0.000 9Ca0.000 11O2, with a Fe concentration of 1.4 mol.%. While ferric ions (Fe3+) are generally accepted to be dominant in the total irons in rutile (e.g., Bromiley and Hilaret, 2005; Bromiley et al., 2004; Swope et al., 1995; Rossman and Smyth, 1990). Among these measured points, one point yields a significantly lower Fe content as compared with the other 7 point, maybe due to the low current and small beam size.

  • A single crystal (120 μm×80 μm×60 μm) was selected for single-crystal XRD at ambient condition on a Rigako XtalAB mini diffractometer (Rigaku, Japan) (Miao et al., 2019). The system was operated at a voltage of 50 kV and a current of 20 mA, equipped with a 600-w rotating Mo-anode X-ray source and a Saturn 724 HG CCD detector (in 1 024×1 024 resolution). We collected the intensity data in a 2θ scanning range from 17.7° to 65.1°, with an averaged Mo Kα1-Kα2 wavelength calibrated to be 0.710 73 Å. The atomic positions as well as the anisotropic displacement parameters (Table S2) were refined by the software package of CrysAlisPro/Olex2 (Dolomanov et al., 2003). Totally, 1 350 equivalent reflections were collected with 69 unique ones. The model fit values are R1=3.25% for all (3.05% for I > 4σ), Rint=4.91% and Goof=1.152. During the structural refinement process, we fixed the Ti4+ and Fe3+ occupancies in the octahedral site to be 98.5% and 1.5%, respectively, on the basis of the chemical composition measured from EPMA. The reported ionic scattering factors were adopted for the cations of Ti4+ and Fe3+ (Cromer and Mann, 1968), as well as O2- anion (Tokonami, 1965).

  • High-temperature XRD measurement was conducted on a PANalytical Empyrean X-ray diffractometer with a Cu-anode X-ray tube, in a 2θ scanning range from 20° to 75°. The ground powder from the sample source was loaded on a commercial resistance-heating Pt stage (Pt purity > 99.99%) mounted in a vacuum chamber. According to high-temperature vibrational measurements (as in the following discussion), significant dehydration in this hydrous rutile sample occurs at 873 K. To avoid any potential dehydration impact and focus on Fe effect on thermal expansion at high temperatures, we directly heated the sample powder to 923 K, and maintained the temperature for one hour. Next, the sample was quenched to 300 K, and then gradually heated to 1 500 K with an increment of 50 K. The temperatures were controlled by an Omega temperature- control unit with a heating rate of 5 K/min and an uncertainty less than 2 K. The peak fitting was fulfilled by the software package Peakfit v4.12 (Sea Solve Software Inc., Massachusetts, USA) for the XRD patterns, as well as the Raman and FTIR spectra in the following discussion. The unit-cell parameters at temperatures were refined by the software UnitCell (Holland and Redfern, 1997).

  • Two sample chips (diameters less than 200 μm) were selected for measuring Raman spectra at high and low temperatures, individually, using a Horiba LabRAM HR Evolution system (HORIBA JobinYvon S.A.S., France) with a micro- confocal spectrometer and an argon ionic laser excitation source (532 nm). One crystal piece was placed on a sapphire window in a Linkam TS 1500 heating stage, and Raman spectra were collected from 300 to 1 473 K with an interval of 50 K, by resistance heating. Throughout the high-temperature experiment, the sample chamber inside the heating stage was filled with N2 for protection. The other chip was loaded on a sapphire plate in a Linkam THMS 600 heating/cooling stage, which is cooled by liquid N2, and Raman spectra were recorded in low temperatures down to 83 K. At each temperature, the spectra were collected in the frequency ranges of 50–1 000 cm-1 for the lattice vibrations and 3 000–3 500 cm-1 for the OH-stretching modes. To make consistent comparison for temperature effect on the signal intensity, we fixed the laser spot size at 1.5 μm, the laser power at 25 mW and the exposure time at 100 s (with 4 repeats) for each spectrum.

    To analyze the water concentration in this natural rutile sample, we chose 6 chips (in diameters of 150–200 μm) for FTIR measurement at room temperature, all of which were firstly double-side polished to thickness of 60–90 μm. The unpolarized FTIR spectra were collected on a Nicolet iS50 FTIR system (Thermofisher, USA), which was coupled with an MCT-A detector (cooled by liquid nitrogen), a continum microscope and a KBr beam-splitter. The IR spectra were collected in the frequency range of 3 000–4 000 cm-1 with an accumulation of 256 scanning times and a resolution of 2 cm-1, and background was also obtained following the measurement on the sample for each spectrum. Next, one of the crystal chips was loaded on the sapphire window of a custom HS1300G- MK2000 external heating stage (INSTC, USA) for in situ high- temperature FTIR measurements in the temperature range from 300 to 1 273 K. Nitrogen was also adopted as protection gas in the sample chamber at high temperatures.

  • In the tetragonal rutile structure (space group: P42/mnm), the Ti4+ cations are coordinated with 6 O2- anions, forming TiO6 octahedra stacked parallel to the c-axis (Swope et al., 1995; Howard et al., 1991). The refined unit-cell parameters for the Fe-bearing natural rutile sample are a=4.604 6(2) Å, c=2.963 9(2) Å and V=62.842(7) Å3, and the atomic position coordinates are: x=y=0.304 9(4) (z=0) for O2- with Ti4+ fixed at the inversion center (0, 0, 0). The Ti-O bond lengths and O…O distances are calculated using the software package Xtaldraw (Downs et al., 1993), and sketched in Fig. 1. In this natural sample, 1.4 mol.% of Ti4+ cations are dominantly substituted by Fe3+, which enlarges both the unit-cell and octahedral TiO6 volumes by 0.7%–0.8%, as compared with the Ti-pure rutile samples (Swope et al., 1995; Howard et al., 1991; Sugiyama and Takéuchi, 1991; Meagher and Lager, 1979). On the other hand, the incorporated protons (H+) coupled with Fe3+ substitution could be detected by infrared spectrum (Lucassen et al., 2012; Bromiley and Hilairet, 2005; Vlassopoulos et al., 1993).

    Figure 1.  The crystal structure of TiO2 rutile. The Ti-O bond lengths and O…O edge distances are calculated from the structure refinement in this study.

    Two IR-active OH-stretching bands are observed for this rutile sample at ambient condition (Fig. 2), and the intensity of Band 1 (at 3 279 cm-1) is higher than that for Band 2 (at 3 297 cm-1), which is consistent with the previous measurements for hydrous Fe-bearing rutile samples (Yang et al., 2011; Bromiley and Hilairet, 2005; Bromiley et al., 2004). The band at 3 279 cm-1 is associated with the reduction of Ti4+ (Ti4+=Ti3++H+) and decoupled with any compositional defects or trivalent cation substitution (Bromiley and Shirvaev, 2006; Hammer and Beran, 1991; Johnson et al., 1973, 1968), while the one at 3 297 cm-1 is coupled with Fe3+ incorporation. Many of the reported studies attributed the OH modes to protonation near the position of (1/2, 1/2, 0), which is along the shared O…O edge of the octahedron in the (001) plane (Bromiley and Shiryaev, 2006; Bromiley and Hilairet, 2005; Swope et al., 1995; Vlassopoulos et al., 1993). In addition, another position at (1/2, 0, 0) is also proposed as a favorable site for protonation in the rutile structure (Koudriachova et al., 2004; Johnson et al., 1968), which is at the channel center outside TiO6 octahedra.

    Figure 2.  Representative IR spectra for this hydrous rutile at ambient condition, with the position of bands 1 and 2 labelled.

    The water concentration in rutile was calculated on the basis of Lambert-Beer Law (Eq. 1)

    where ε is the absorption coefficient, γ is the parameter for the orientation factor, while d is thickness of the sample. I0(v) and I(v) are the intensities of the incoming and transmitted radiation at the frequency v, respectively. Here, we adopt the absorption coefficients from Maldener et al. (2001) (38 000 L·mol-1·cm-2) and Johnson et al. (1973) (30 200 L·mol-1·cm-2), and set the orientation factor to be 1/3 for unpolarized FTIR spectra. The IR absorbance is integrated in the frequency range of 3 200–3 400 cm-1 for each measured point. The 3 to 5 points were measured at different locations on each of these 6 crystal pieces, and the averaged water content (over 20 measurements) with standard deviation of 4 350±670 H/106 Ti (CH2O=490±75 ppmw.) by the calibration from Maldener et al. (2001), while 5 470±840 H/106 Ti (CH2O=620±95 ppmw.) from Johnson et al. (1973). The EPMA analysis gives a Fe content of 1.4 mol.% (14 000 Fe/106 Ti), which is more than 20 times of the H atomic concentration in this rutile sample and accounts for 86.5 mol.% of the incorporated trivalent cations (M3+) in this rutile sample. Hence, there should be two ways for M3+ (mainly Fe3+) incorporation: the electrostatically coupled substitution (Ti4+=Fe3++H+) and the substitution causing oxygen vacancies (2Ti4+=2Fe3++OV), while the latter one might be dominant in this natural rutile. Such trivalent cation substitution mechanism is similar to that in Al-bearing SiO2 stishovite (Si4+=Al3++H+ together with 2Si4+= 2Al3++OV) (e.g., Litasov et al., 2007; Pawley et al., 1993).

  • The powder XRD pattern at T=300 K (Fig. 3) was obtained when quenched from 923 K after significant dehydration, and then the sample powder was gradually heated up to 1 500 K. The unit-cell parameters at various temperatures were refined by at least 7 reflection lines out of (110), (100), (200), (111), (210), (211), (220), (002), (310), (301) and (112) (Table S3). At ambient condition, the unit-cell parameters (a, c and V) quenched from 923 K (by powder XRD) agree with the ones before any heating (by single-crystal XRD), within the experimental uncertainty. Hence, we speculate that such a water concentration (CH2O < 700 ppmw.) should have little impact on the unit cell. Another XRD pattern was also measured at room temperature (noted as 'quench' pattern in Fig. 3) when quenched from 1 500 K, and the reflection pattern is quite consistent with that quenched from 923 K, implying that rutile was stable without any phase transition at high temperatures up to 1 500 K at ambient pressure.

    Figure 3.  XRD patterns obtained at 300 K (middle) and 1 500 K (top), as well as quenched from 1 500 K (bottom). The Bragg's peaks for rutile are indexed, and some of the Pt reflection lines are marked for the pattern measured at 300 K.

    Variations of the a and c axes with temperature are plotted in Fig. 4a, which have been normalized to the ones at 300 K. The averaged axial thermal expansion coefficients are 9.25(8)× 10-6 K-1 (R2=0.994 7) and 11.98(8)×10-6 K-1 (R2=0.999 4) for the a and c axes, respectively, which are quite consistent with the previous measurements (Hummer et al., 2007; Sugiyama and Takéuchi, 1991). The c axis shows larger thermal expansion coefficient as compared with the a-axis due to the increased TiO6 octahedral distortion at elevated temperatures. Hummer et al. (2007) conducted high-temperature synchrotron powder XRD measurement up to 575 K. Sugiyama and Takéuchi (1991) carried out single-crystal XRD experiment up to 1 873 K but with larger temperature intervals (fewer data points) as compared with this study, and part of their dataset (within 1 500 K) was shown in Fig. 4a. In addition, both the studies took measurements on synthetic Ti-pure rutile sample, while we adopted the natural sample with 1.4 mol.% Fe in this study. Good agreement among these three datasets suggests that such Fe concentration should not have significant effect on the thermal expansivity for rutile.

    Figure 4.  (a) Variations of the a and c axes with temperature, which are normalized to the ones at 300 K. Comparison is also made with the literatures (Hummer et al., 2007; Sugiyama and Takéuchi, 1991). (b) The unit-cell volume as a function of temperature with the fitting curves by Suzuki (Eq. 4) and Kumar (Eq. 5) equations. The inset shows the fit residue for the volumes.

    The thermal expansion coefficient (α), which describes the variation of volume as a function of temperature, is defined as

    Various function forms have been proposed for α as a function of T at P=0 GPa, and a famous one is proposed by Fei (1995) as below

    The fitted Fei Equation on this dataset yields: α0= 25.40(7)×10-6 K-1, α1=6.93(8)×10-9 K-2 and α2= -0.668(8)×10-6 K. Besides, Suzuki (1975), Suzuki et al. (1979) and Kumar(2003, 1996, 1995) established the correlation between the volume and temperature on the basis of the Mie-Grüneisen- Debye Equation of state, which are believed to be more accurate at high temperatures well above the Debye temperature. The Suzuki and Kumar equations are expressed as in Eqs. (4) and (5), respectively

    In the above equations, Q0=V0(0)·KT0(0)/γMGD, and k= (KT'–1)/2. V0(0) and KT0(0) are the volume and isothermal bulk modulus at P=0 GPa and T=0 K, and the pressure derivative of the isothermal bulk modulus KT'=6.5 (Arlt et al., 2000). The thermal energy Eth(T) is constructed on the Debye model

    where R is the gas constant, n is the number of atoms in the formula (3 for rutile), while ΘD is the Debye temperature, which could be derived in the acoustic mode

    where h, k and N are the Boltzmann, Plank and Avogadro's constants, respectively. The molar mass M=79.9 g/mol and the density ρ=4.233 g/cm3 for rutile, and the mean seismic velocity Vm can be calculated as in Eq. (8)

    Isaak et al. (1998) reported the seismic velocities for rutile at ambient condition: VP=9.24(7) km/s and VP=5.16(8) km/s, and we can derive the mean velocity Vm=4.67(9) km/s and the acoustic ΘD=636(17) K. Our V-T dataset was fitted by Suzuki and Kumar equations (Fig. 4b), and the differences between the fitted and measured volumes at high temperatures are generally within ±0.02 Å3, which are significantly smaller than the uncertainties of measurement. The fitted unit-cell volume and Q0 parameter at T=0 K are: V0(0)=62.50(12) Å3 (18.812(4) cm3/mol) and Q0=2.63(1)×106 J·mol-1·K-1 for Kumar Equation, while V0(0)=62.48(14) Å3 (18.806(4) cm3/mol) and Q0= 2.72(1)×106 J·mol-1·K-1 for Suzuki Equation. On the basis of the measured KT0(300 K)=210.3 GPa and ∂KT/∂T= -0.05 GPa/K (Isaak et al., 1998), it could be obtained that KT0 (0 K)=225.3 GPa, as well as the Grüneisen parameter γMGD=1.56 for Kumar Equation, while 1.61 for Suzuki Equation.

    The volumetric thermal expansion coefficients (αV), fitted from Fei, Suzuki and Kumar equations, are plotted as a function of temperature in Fig. 5, and they agree well with each other within a discrepancy of ±3% when extrapolated to 2 000 K. Our results are also compared with the data in the literatures (Henderson et al., 2009; Hummer et al., 2007; Saxena et al., 1993; Sugiyama and Takéuchi, 1991; Touloukian and Kirby, 1977; Rao et al., 1970). According to the Debye model, the thermal expansion coefficients for materials generally increase with temperature increasing, while the αV profiles from this study are located between those from Touloukian and Kirby (1977) and Saxena et al. (1993) at high temperatures above 800 K. On the other hand, the averaged thermal expansion coefficient (α0) from this study is 30.48(5)×10-6 K-1, which is 5%–30% larger as compared with the previous studies (Henderson et al., 2009; Hummer et al., 2007; Sugiyama and Takéuchi, 1991; Rao et al., 1970).

    Figure 5.  The volumetric thermal expansion coefficient (αV) as a function of temperature. Comparison is made between this study (bolded curves) and the previous studies (normal dotted curves; a. Rao et al., 1970; b. Henderson et al., 2009; c. Hummer et al., 2007; d. Sugiyama and Takéuchi, 1991; e. Touloukian and Kirby, 1977; f. Saxena et al., 1993).

  • There are 15 optical vibrational modes in rutile with irreducible representation in total: 1A1g(R)+1A2g (inactive)+1A2u(I)+ 1B1g(R)+1B2g(R)+2B1u(I)+1Eg(R)+3Eu(I) (R: Raman-active; I: infrared-active) (Lan et al., 2012; Hemley et al., 1986; Mammone et al., 1980; Porto et al., 1967). The selected Raman spectra for the lattice vibrations (below 1 000 cm-1) at low and high temperatures are shown in Fig. 6. The Eg (O-Ti-O bending) and A1g (asymmetric Ti-O stretching) modes are observed around 440 and 610 cm-1, respectively, with quite strong intensities and similar half-height widths. The B1g band (TiO6 octahedron rotation around the c axis) is detected to have a sharp peak around 140 cm-1 with much lower intensity, while B2g (symmetric Ti-O stretching) appears as a weak and broad band above 810 cm-1, which could only be observed at the temperatures below 400 K. In addition, the multi-phonon process is observed as a broad 'hump' around 230 cm-1, which is caused by the anharmonic feature as well as disorder in the rutile structure (Lan et al., 2012; Balachandran and Eror, 1982; Hara and Nicol, 1979).

    Figure 6.  Representative Raman spectra for the lattice vibrations (including the multi-phonon process) at low and high temperatures. The vertical dashed lines stand for the peak positions of the modes at room temperature (RT), and the backgrounds of the black-body radiation have been subtracted.

    The black-body radiation got stronger with temperature increasing, while the intensities of the vibrational bands (including the multi-phonon process) systematically become weaker at elevated temperature. Variations of these modes with temperature are plotted in Fig. 7, and the slopes ((∂vi/∂T), cm-1·K-1) from the linear regressions are compared with the data in the literatures (Lan et al., 2012; Samara and Peercy, 1973) in Table 1. The internal Ti-O stretching (A1g, B2g) and O-Ti-O bending (Eg) modes systematically shift to lower frequencies at elevated temperature, since the covalent Ti-O bonds get elongated during the thermal expansion procedure (Sugiyama and Takéuchi, 1991). The B1g mode is nearly temperature independent, implying that temperature has little impact on the rotation of the TiO6 octahedron. On the other hand, the multi-phonon process exhibits 'blue-shift' at higher temperature, which is in accordance with the fact that the anharmonic features, as well as disorder in the crystal structure, increases with temperature increasing.

    Figure 7.  Evolution of the Raman shifts for the lattice modes (including the multi-phonon process) with temperature increasing.

    Assignment vi (cm-1) (∂vi/∂T)P (cm-1·K-1)
    Lattice vibrations This study Lan et al. (2012) Samara and Peercy (1973)
    B1g 142 0.002(3) 0.001 0.000 9(6)
    Multi-phonon 232 0.040(6) -- --
    Eg 439 -0.032(5) -0.049 -0.028(2)
    A1g 608 -0.011(4) -0.009 0.003 7(2)
    B2g 810 -0.044(8) -- --
    OH-stretching This study (IR-active) This study (Raman-active) Yang et al. (2011) Guo (2017)
    Band 1 3 279 -0.056(2) -0.059(4) -0.021(3) -0.083
    Band 2 3 297 -0.082(3) -0.056(3) -0.049(3) --
    Merged band 3 245a -0.048(2) -0.069(2) -- --
    a. Measured at 923 K by FTIR spectrum.

    Table 1.  The temperature-dependence (∂vi/∂T) P of the frequencies for both the lattice and OH-stretching vibrations

    In addition, the microscopic isobaric Grüneisen parameter (γiP), describing the evolution of the mode frequency with temperature at fixed pressure, is defined below

    Taking the average thermal expansion coefficient from this study (α0=30.48(5)×10-6 K-1), we derived the γiP parameters for the lattice vibrational modes: -0.5(7) for B1g, +2.4(3) for Eg, +0.6(2) for A1g, and +1.8(3) for B2g.

  • The OH-stretching bands 1 and 2 are also detected by Raman spectra at 3 283 and 3 293 cm-1 (at 300 K in Fig. 8a), which agree well with the IR-active ones (Fig. 8b). The shifts of these OH-stretching bands are recorded by high-temperature FTIR and Raman spectra up to 1 273 K, as well as low-T Raman spectra down to 123 K. Around a temperature of 873 K, bands 1 and 2 (for both Raman-active and IR-active modes) merge completely into a single band. While the OH-stretching bands are still deconvoluted into two bands at the temperatures below 873 K, so as to better describe the thermal behaviors for bands 1 and 2. The Raman-active OH-stretching band cannot be detected above 1 073 K due to strong black-body radiation, but can still be recovered when quenched from 1 273 K (Fig. 8c).

    Figure 8.  Selected Raman (a) and FTIR (b) spectra for the OH-stretching bands measured at various temperatures. The signals for the Raman (at 1 073 K) and FTIR (at 1 273 K) spectra are magnified for clarity. The Raman (c) and FTIR (d) spectra, obtained when quenched from high temperatures, are compared with the one before heating. Background has been subtracted for each spectrum.

    Both the Raman-active and IR-active OH-stretching modes systematically shift to lower frequencies at higher temperature (Fig. 9), with the decreasing rates ((∂vi/∂T), cm-1·K-1) listed in Table 1. Similar phenomenon for the 'red-shift' of OH-stretching bands is also observed by other FTIR measurements (Guo, 2017; Yang et al., 2011). According to the empirical correlation between the hydrogen bond length (dO…H) and the frequency (vi) of OH-stretching mode (Libowitzky, 1999), the OH bands in rutile should correspond to an O…H bond length about 1.85 Å as well as an O…O distance of 2.75 Å. While the shared O…O edge for protonation is much shorter as measured by single-crystal XRD (dO…O=2.542 Å in Fig. 1). Therefore, the O-H…O bond must be nonlinear, and the shift of the OH-stretching frequency might be dominantly determined by the elongation of the covalent O-H band itself at high temperature (Mookherjee et al., 2001). In addition, the IR-active band at 3 279 cm-1 (decoupled with Fe3+ substitution) shows the temperature-dependence in a larger magnitude as compared with the one at 3 297 cm-1 (coupled with Fe3+ substitution), and similar phenomenon was also reported by Yang et al. (2011), which was attributed to the fact that the electronegativity of Ti4+ is larger than that for Fe3+ (Li and Xue, 2006).

    Figure 9.  The frequencies of IR-active (solid symbols) and Raman-active (open symbols) OH-stretching modes as a function of temperature. The vertical line represents T=900 K, around which bands 1 (five-star) and 2 (circles) completely merge into one single band (triangle). The vertical error bars for the full-width of half maximum are presented if larger than the sizes of the symbols.

    The integral IR absorbance and Raman signal intensity for the whole OH-stretching bands are plotted as a function of temperature in Fig. 10a. To make a consistent comparison, the Raman spectra at different temperatures were collected at the constant experimental condition (including the incident laser power, beam spot size as well as the exposure duration). The intensities for both Raman and IR signals decrease abruptly at a temperature of around 873 K, due to the factors of both dehydration and smaller absorption coefficient (ε) at higher temperatures. For most hydrous minerals, the absorbance (logarithm for the ratio between I0(v) and I(v) as the numerator in Eq. (1)) generally becomes smaller at elevated temperatures even without dehydration (CH2O remains constant), suggesting negative dependence between the absorption coefficient (in the denominator of Eq. (1)) and temperature. On the other hand, the Raman signal intensity decreases to 58% and 16%, when quenched from 873 and 1 273 K, individually, with respect to that before heating (Fig. 8c). While the integral IR absorbance decreases to 56% and 15% (Fig. 8d), when quenched from 823 and 1 273 K, respectively, hence, we speculate about 43% dehydration by 850 K, and 85% dehydration by 1 273 K, according to the quenched spectra. We also checked the variations of bands 1 and 2, separately, in the temperature range up to 873 K (Fig. 10b), and the intensities for each band have been normalized to the one at 300 K. Both the Raman and FTIR results support the general trend that the intensities of OH-stretching bands decrease with temperature increasing, and partial dehydration may happen at both the decoupled and coupled H sites in this rutile structure. It should be also noted that at each time, the sample was quenched immediately with power off, and the temperature was cooled down below 500 K within half a minute.

    Figure 10.  (a) The integral IR absorbance and Raman intensity for the OH-stretching bands as a function of temperature. (b) Variations of the intensities for bands 1 and 2 with temperature below 900 K (solid symbols: IR-active; open symbols: Raman-active). The intensities have been normalized to the ones at 300 K for IR-active and Raman-active signals, respectively.

  • In this study, we measured single-crystal XRD as well as in situ high-temperature powder XRD, Raman and FTIR spectra on a natural TiO2 rutile sample. EPMA analysis indicates an Fe concentration of 1.4 mol.%, while the unpolarized FTIR spectra give an average H2O content of 510±120 ppmw. Trivalent cations (M3+) are incorporated into the rutile structure in both mechanisms of Ti4+=M3++H+ and 2Ti4+=2M3++OV, which is similar to Al3+ incorporation in SiO2 stishovite. Such Fe content increases both the unit-cell and TiO6 octahedral volumes by 0.7%–0.8%, as compared with those for Ti-pure samples. High-pressure and high-temperature XRD measurements in future are necessary for constraining equations of state for the Fe-bearing rutile samples, which is important for understanding the metallic cation substitution mechanisms at high-P/T conditions, since significant amounts of trivalent (and even divalent) cations can be incorporated into the rutile structure deep in the Earth.

    The unit-cell parameters are measured in the temperature range from 300 to 1 500 K, and the thermal expansion coefficient (α) is fitted by Fei, Suzuki and Kumar equations. All these three equations yield quite consistent results even when extrapolated to 2 000 K, with an averaged value of 30.48(5)×10-6 K-1. Our measurement indicates that such an iron concentration should have little impact on the thermal expansivity for rutile, as compared with previous studies on the TiO2-pure samples.

    According to the Raman spectra measured in a wide temperature range from 83 to 1 473 K, the internal Ti-O stretching (A1g and B2g) and O-Ti-O bending (Eg) modes shift to lower frequencies at elevated temperature, while the TiO6 octahedron rotation (B1g) is almost independent with temperature. On the other hand, the multi-phonon process shows blue shift with temperature increasing, which is consistent with the enhanced anharmonicity in the rutile structure at higher temperature.

    The OH-stretching bands at 3 279 and 3 297 cm-1, which are decoupled and coupled with Fe3+ substitution, respectively, can be observed at high temperatures up to 1 273 K. Both the Raman-active and IR-active OH-stretching modes systematically show 'red shift' at elevated temperature, with the signal intensities getting weaker. We propose about 43% dehydration around 873 K while 85% dehydration at 1 273 K, on the basis of the quenched vibrational spectra from high temperatures. Our FTIR measurement on OH vibration achieved much higher temperature than previous studies, and part of the water can still be retained in the lattice even at such high temperatures, which has not been reported before. Rutile could also be a potential water carrier in the mantle, like in the subduction zone.

  • This work was supported by the National Key Research and Development Program of China (No. 2016YFC0600204), and the National Natural Science Foundation of China (Nos. 41590621 and 41672041). The in situ high-temperature XRD, Raman and FTIR, as well as EPMA were conducted at China University of Geosciences (Wuhan). The single-crystal XRD at ambient condition was measured at Huazhong University of Science and Technology, and many thanks go to Yan Qin for his experimental assistance. The final publication is available at Springer via https://doi.org/10.1007/s12583-020-1351-5.

    Electronic Supplementary Materials: Supplementary materials (Tables S1–S3) are available in the online version of this article at https://doi.org/10.1007/s12583-020-1351-5.

Reference (66)

Catalog

    /

    DownLoad:  Full-Size Img  PowerPoint
    Return
    Return