Journal
PHYSICAL REVIEW B
Volume 90, Issue 9, Pages -Publisher
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevB.90.094114
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Funding
- American Chemical Society Petroleum Research Fund [52138-DNI10]
- U.S. DOE, Office of Basic Energy Sciences (BES) [DE-AC02-06CH11357]
- National Science Foundation Grant [OCI-1053575]
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Using first-principles density functional theory calculations, we investigate the hydrostatic pressure-induced reorientation of the Mn-F Jahn-Teller bond axis in the fluoride cryolite Na3MnF6. We find that a first-order isosymmetric phase transition (IPT) occurs between crystallographically equivalent monoclinic structures at approximately 2.15 GPa, consistent with earlier experimental studies. Mode-crystallography analyses of the pressure-dependent structures in the vicinity of the transition reveal a clear evolution of the Jahn-Teller bond distortions in cooperation with an asymmetrical stretching of the equatorial fluorine atoms in the MnF6 octahedral units. We identify a significant (70%) change in the orbital occupancy of the e(g) manifold of the 3d(4) Mn(III) to be responsible for the transition, stabilizing one monoclinic P2(1)/n variant over the other. The orbital reconstruction as a driving force for the transition is confirmed by analogous calculations of isostructural 3d(0) Na3ScF6, which shows no evidence of an IPT up to 6.82 GPa.
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