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Title: Phase transitions and equations of state of alkaline earth fluorides CaF[subscript 2], SrF[subscript 2], and BaF[subscript 2] to Mbar pressures

Abstract

Phase transitions and equations of state of the alkaline earth fluorides CaF{sub 2}, SrF{sub 2}, and BaF{sub 2} were examined by static compression to pressures as high as 146 GPa. Angle-dispersive x-ray diffraction experiments were performed on polycrystalline samples in the laser-heated diamond-anvil cell. We confirmed that at pressures less than 10 GPa all three materials undergo a phase transition from the cubic (Fm{bar 3} m) fluorite structure to the orthorhombic (Pnam) cotunnite-type structure. This work has characterized an additional phase transition in CaF{sub 2} and SrF{sub 2}: these materials were observed to transform to a hexagonal (P6{sub 3}/mmc) Ni{sub 2}In-type structure between 63-79 GPa and 28-29 GPa, respectively, upon laser heating. For SrF{sub 2}, the Ni{sub 2}In-type phase was confirmed by Rietveld refinement. Volumes were determined as a function of pressure for all high-pressure phases and fit to the third-order Birch-Murnaghan equation of state. For CaF{sub 2} and SrF{sub 2}, the fluorite-cotunnite transition results in a volume decrease of 8-10%, while the bulk modulus of the cotunnite-type phase is the same or less than that of the fluorite phase within uncertainty. For all three fluorides, the volume reduction associated with the further transition to the Ni{sub 2}In-type phase ismore » {approx}5%. The percentage increase in the bulk modulus ({Delta}K) across the transition is greater when the cation is smaller. While for BaF{sub 2}, {Delta}K is 10-30%, {Delta}K values for SrF{sub 2} and CaF{sub 2} are 45-65% and 20-40%. Although shock data for CaF{sub 2} have been interpreted to show a transition to a highly incompressible phase above 100 GPa, this is not consistent with our static equation of state data.« less

Authors:
; ; ; ; ; ;  [1]
  1. Princeton
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Org.:
USDOE
OSTI Identifier:
1002454
Resource Type:
Journal Article
Journal Name:
Phys. Rev. B
Additional Journal Information:
Journal Volume: 81; Journal Issue: (17) ; 2010; Journal ID: ISSN 1098-0121
Country of Publication:
United States
Language:
ENGLISH
Subject:
36 MATERIALS SCIENCE; EQUATIONS OF STATE; CRYSTAL-PHASE TRANSFORMATIONS; CALCIUM FLUORIDES; STRONTIUM FLUORIDES; BARIUM FLUORIDES; PRESSURE RANGE GIGA PA; X-RAY DIFFRACTION

Citation Formats

Dorfman, Susannah M, Jiang, Fuming, Mao, Zhu, Kubo, Atsushi, Meng, Yue, Prakapenka, Vitali B, Duffy, Thomas S, CIW), and UC). Phase transitions and equations of state of alkaline earth fluorides CaF[subscript 2], SrF[subscript 2], and BaF[subscript 2] to Mbar pressures. United States: N. p., 2010. Web. doi:10.1103/PhysRevB.81.174121.
Dorfman, Susannah M, Jiang, Fuming, Mao, Zhu, Kubo, Atsushi, Meng, Yue, Prakapenka, Vitali B, Duffy, Thomas S, CIW), & UC). Phase transitions and equations of state of alkaline earth fluorides CaF[subscript 2], SrF[subscript 2], and BaF[subscript 2] to Mbar pressures. United States. doi:10.1103/PhysRevB.81.174121.
Dorfman, Susannah M, Jiang, Fuming, Mao, Zhu, Kubo, Atsushi, Meng, Yue, Prakapenka, Vitali B, Duffy, Thomas S, CIW), and UC). Mon . "Phase transitions and equations of state of alkaline earth fluorides CaF[subscript 2], SrF[subscript 2], and BaF[subscript 2] to Mbar pressures". United States. doi:10.1103/PhysRevB.81.174121.
@article{osti_1002454,
title = {Phase transitions and equations of state of alkaline earth fluorides CaF[subscript 2], SrF[subscript 2], and BaF[subscript 2] to Mbar pressures},
author = {Dorfman, Susannah M and Jiang, Fuming and Mao, Zhu and Kubo, Atsushi and Meng, Yue and Prakapenka, Vitali B and Duffy, Thomas S and CIW) and UC)},
abstractNote = {Phase transitions and equations of state of the alkaline earth fluorides CaF{sub 2}, SrF{sub 2}, and BaF{sub 2} were examined by static compression to pressures as high as 146 GPa. Angle-dispersive x-ray diffraction experiments were performed on polycrystalline samples in the laser-heated diamond-anvil cell. We confirmed that at pressures less than 10 GPa all three materials undergo a phase transition from the cubic (Fm{bar 3} m) fluorite structure to the orthorhombic (Pnam) cotunnite-type structure. This work has characterized an additional phase transition in CaF{sub 2} and SrF{sub 2}: these materials were observed to transform to a hexagonal (P6{sub 3}/mmc) Ni{sub 2}In-type structure between 63-79 GPa and 28-29 GPa, respectively, upon laser heating. For SrF{sub 2}, the Ni{sub 2}In-type phase was confirmed by Rietveld refinement. Volumes were determined as a function of pressure for all high-pressure phases and fit to the third-order Birch-Murnaghan equation of state. For CaF{sub 2} and SrF{sub 2}, the fluorite-cotunnite transition results in a volume decrease of 8-10%, while the bulk modulus of the cotunnite-type phase is the same or less than that of the fluorite phase within uncertainty. For all three fluorides, the volume reduction associated with the further transition to the Ni{sub 2}In-type phase is {approx}5%. The percentage increase in the bulk modulus ({Delta}K) across the transition is greater when the cation is smaller. While for BaF{sub 2}, {Delta}K is 10-30%, {Delta}K values for SrF{sub 2} and CaF{sub 2} are 45-65% and 20-40%. Although shock data for CaF{sub 2} have been interpreted to show a transition to a highly incompressible phase above 100 GPa, this is not consistent with our static equation of state data.},
doi = {10.1103/PhysRevB.81.174121},
journal = {Phys. Rev. B},
issn = {1098-0121},
number = (17) ; 2010,
volume = 81,
place = {United States},
year = {2010},
month = {6}
}