TY - JOUR
T1 - Microscopic origin of pressure-induced isosymmetric transitions in fluoromanganate cryolites
AU - Charles, Nenian
AU - Rondinelli, James M.
N1 - Publisher Copyright:
© 2014 American Physical Society.
PY - 2014/9/24
Y1 - 2014/9/24
N2 - 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 eg manifold of the 3d4 Mn(III) to be responsible for the transition, stabilizing one monoclinic P21/n variant over the other. The orbital reconstruction as a driving force for the transition is confirmed by analogous calculations of isostructural 3d0 Na3ScF6, which shows no evidence of an IPT up to 6.82 GPa.
AB - 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 eg manifold of the 3d4 Mn(III) to be responsible for the transition, stabilizing one monoclinic P21/n variant over the other. The orbital reconstruction as a driving force for the transition is confirmed by analogous calculations of isostructural 3d0 Na3ScF6, which shows no evidence of an IPT up to 6.82 GPa.
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U2 - 10.1103/PhysRevB.90.094114
DO - 10.1103/PhysRevB.90.094114
M3 - Article
AN - SCOPUS:84907452480
SN - 1098-0121
VL - 90
JO - Physical Review B - Condensed Matter and Materials Physics
JF - Physical Review B - Condensed Matter and Materials Physics
IS - 9
M1 - 094114
ER -