Screw- Type Motion and Its Impact on Cooperativity in BaNa2 Fe[VO4 ]2

Inorganic Chemistry
Anna ReußAngela Möller

Abstract

BaNa2Fe[VO4]2 contains a Jahn-Teller active ion (FeII, 3d6, high-spin) in an octahedral coordination. On the basis of a combination of temperature-dependent X-ray diffraction and Mössbauer and Raman spectroscopies, we demonstrate the coupling of lattice dynamics with the electronic ground state of FeII. We identify three lattice modes combined to an effective canted screw- type motion that drives the structural transition around room temperature from the high-temperature ( P3̅) via intermediate phases to the low-temperature phase ( C2/ c). The dynamics of the electronic ground state of Fe(II) are evident from Mössbauer data with signatures of a motion-narrowed doublet above 320 K, a gradual evolution of the 5Eg electronic state below 293 K, and finally the signature of the thermodynamically preferred orbitally nondegenerate ground state (5Ag) of Fe(II) below 100 K. The continuous nature of the transition is associated with the temperature-dependent phonon parameters derived from Raman spectroscopy, which point out the presence of strong electron-phonon coupling in this compound. We present a microscopic mechanism and evaluate the collective component leading to the structural phase transition.

References

Mar 1, 1993·Physical Review. B, Condensed Matter·Z Yi-Yang, Y Chun-Hao
Feb 21, 2006·Acta Crystallographica. Section A, Foundations of Crystallography·Mois I AroyoHans Wondratschek
Feb 21, 2013·Journal of Physics. Condensed Matter : an Institute of Physics Journal·Genki NakayamaHiroyuki Nojiri
Aug 24, 2013·Journal of the American Chemical Society·Rénald DavidOlivier Mentré

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Citations

Jul 4, 2019·Proceedings of the National Academy of Sciences of the United States of America·Ruidan ZhongRobert J Cava

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