Thermodynamic investigation of the phase equilibrium boundary between TiO2 rutile and its α-PbO2-type high-pressure polymorph

Thermodynamic investigation of the phase equilibrium boundary between TiO2 rutile and its... Heat capacity (C ) of rutile and α-PbO type T iO (TiO -II) were measured by the differential scanning calorimetry and P 2 2 2 thermal relaxation method. Using the results, standard entropies at 1 atm and 298.15 K of rutile and TiO -II were determined to be 50.04(4) and 46.54(2) J/mol K, respectively. Furthermore, thermal expansivity (α) determined by high-temperature X-ray diffraction measurement and mode Grüneisen parameters obtained by high-pressure Raman spectroscopy suggested the thermal Grüneisen parameter (γ ) for T iO -II of 1.7(1). By applying the obtained low-temperature C and γ , the meas- th 2 P th ured C and α data of TiO -II were extrapolated to higher temperature region using a lattice vibrational model calculation, P 2 as well as rutile. Internally consistent thermodynamic data sets of both rutile and TiO -II assessed in this study were used to thermodynamically calculate the rutile‒TiO -II phase equilibrium boundary. The most plausible boundary was obtained to be P (GPa) = 0.0074T (K) − 1.7. Our boundary suggests that the crystal growth of TiO -II observed below 5.5 GPa and 900 K in previous studies advanced in its stability field. The phase boundary calculation also suggested small, exothermic phase transition enthalpy from http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Physics and Chemistry of Minerals Springer Journals

Thermodynamic investigation of the phase equilibrium boundary between TiO2 rutile and its α-PbO2-type high-pressure polymorph

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Publisher
Springer Journals
Copyright
Copyright © 2018 by Springer-Verlag GmbH Germany, part of Springer Nature
Subject
Earth Sciences; Mineralogy; Crystallography and Scattering Methods; Geochemistry; Mineral Resources
ISSN
0342-1791
eISSN
1432-2021
D.O.I.
10.1007/s00269-018-0977-7
Publisher site
See Article on Publisher Site

Abstract

Heat capacity (C ) of rutile and α-PbO type T iO (TiO -II) were measured by the differential scanning calorimetry and P 2 2 2 thermal relaxation method. Using the results, standard entropies at 1 atm and 298.15 K of rutile and TiO -II were determined to be 50.04(4) and 46.54(2) J/mol K, respectively. Furthermore, thermal expansivity (α) determined by high-temperature X-ray diffraction measurement and mode Grüneisen parameters obtained by high-pressure Raman spectroscopy suggested the thermal Grüneisen parameter (γ ) for T iO -II of 1.7(1). By applying the obtained low-temperature C and γ , the meas- th 2 P th ured C and α data of TiO -II were extrapolated to higher temperature region using a lattice vibrational model calculation, P 2 as well as rutile. Internally consistent thermodynamic data sets of both rutile and TiO -II assessed in this study were used to thermodynamically calculate the rutile‒TiO -II phase equilibrium boundary. The most plausible boundary was obtained to be P (GPa) = 0.0074T (K) − 1.7. Our boundary suggests that the crystal growth of TiO -II observed below 5.5 GPa and 900 K in previous studies advanced in its stability field. The phase boundary calculation also suggested small, exothermic phase transition enthalpy from

Journal

Physics and Chemistry of MineralsSpringer Journals

Published: Jun 4, 2018

References

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