TY - JOUR

T1 - Experimental and Ab Initio Investigation of the Formation of Phosphoran Olivine

AU - Bekker, Tatyana

AU - Litasov, Konstantin

AU - Shatskiy, Anton

AU - Sagatov, Nursultan

AU - Podborodnikov, Ivan

AU - Krinitsin, Pavel

N1 - Funding Information: We thank the reviewers for valuable suggestions, which improved the quality of the manuscript. This work was performed under the state assignment project of IGM SB RAS. K.L. is supported by the state assignment of IHPP RAS. SEM/EDS and XRD experiments were supported by the Russian Science Foundation #17-17-01177. Publisher Copyright: © 2021 American Chemical Society. All rights reserved. Copyright: Copyright 2021 Elsevier B.V., All rights reserved.

PY - 2021/6/17

Y1 - 2021/6/17

N2 - With the use of both experimental and numerical methods, the conditions required for phosphoran olivine formation as well as its structural features and thermodynamic stability have been studied. Olivine containing up to 35 wt % P2O5 was synthesized in evacuated quartz glass ampoules at temperatures of 1373, 1473, and 1573 K using San Carlos olivine or an oxide mixture blended with either magnesium phosphate Mg3(PO4)2 or iron phosphide FeP and studied by scanning electron microscopy/energy-dispersive spectrometry, wavelength-dispersive spectroscopy analysis, X-ray powder diffraction, and Raman spectroscopy. The inhomogeneity of the composition of synthesized phosphoran olivines as well as the results of first-principles calculations unequivocally indicates their metastable crystallization. The absence of the shift of phosphoran olivine X-ray diffraction reflections with respect to phosphoran-free olivine might indicate that the entry of phosphorus in olivine causes only a slight distortion of the structure, which is consistent with the results of first-principles calculations. The position of the Raman bands associated with the most intensive internal vibration modes of [SiO4]4- tetrahedra at 824 and 857 cm-1 and [PO4]3- tetrahedra at 981 cm-1 does not change with respect to phosphoran-free olivine and farringtonite, respectively. Their relative intensities in phosphoran olivine may reflect the Si/P ratio. The phosphoran olivine formation energy is dependent on the distance between [PO4]3- tetrahedra in the structure. With the use of first-principles calculations, it has been shown that neither pressure in the range from 0 to 8 GPa nor temperature in the range from 0 to 1500 K favors the equilibrium entry of phosphorus into olivine at concentrations equal to or exceeding 6.3 wt %.

AB - With the use of both experimental and numerical methods, the conditions required for phosphoran olivine formation as well as its structural features and thermodynamic stability have been studied. Olivine containing up to 35 wt % P2O5 was synthesized in evacuated quartz glass ampoules at temperatures of 1373, 1473, and 1573 K using San Carlos olivine or an oxide mixture blended with either magnesium phosphate Mg3(PO4)2 or iron phosphide FeP and studied by scanning electron microscopy/energy-dispersive spectrometry, wavelength-dispersive spectroscopy analysis, X-ray powder diffraction, and Raman spectroscopy. The inhomogeneity of the composition of synthesized phosphoran olivines as well as the results of first-principles calculations unequivocally indicates their metastable crystallization. The absence of the shift of phosphoran olivine X-ray diffraction reflections with respect to phosphoran-free olivine might indicate that the entry of phosphorus in olivine causes only a slight distortion of the structure, which is consistent with the results of first-principles calculations. The position of the Raman bands associated with the most intensive internal vibration modes of [SiO4]4- tetrahedra at 824 and 857 cm-1 and [PO4]3- tetrahedra at 981 cm-1 does not change with respect to phosphoran-free olivine and farringtonite, respectively. Their relative intensities in phosphoran olivine may reflect the Si/P ratio. The phosphoran olivine formation energy is dependent on the distance between [PO4]3- tetrahedra in the structure. With the use of first-principles calculations, it has been shown that neither pressure in the range from 0 to 8 GPa nor temperature in the range from 0 to 1500 K favors the equilibrium entry of phosphorus into olivine at concentrations equal to or exceeding 6.3 wt %.

KW - first-principles calculations

KW - phosphoran olivine

KW - Raman spectroscopy

KW - solid-state synthesis

KW - X-ray powder diffraction

UR - http://www.scopus.com/inward/record.url?scp=85108630780&partnerID=8YFLogxK

U2 - 10.1021/acsearthspacechem.1c00011

DO - 10.1021/acsearthspacechem.1c00011

M3 - Article

AN - SCOPUS:85108630780

VL - 5

SP - 1373

EP - 1383

JO - ACS Earth and Space Chemistry

JF - ACS Earth and Space Chemistry

SN - 2472-3452

IS - 6

ER -