Screw- Type Motion and Its Impact on Cooperativity in BaNa 2 Fe[VO 4 ] 2

• Published in: Inorganic chemistry Vol. 57; no. 11; pp. 6300 - 6308
• Main Authors: Reuß, Anna, Ksenofontov, Vadim, Tapp, Joshua, Wulferding, Dirk, Lemmens, Peter, Panthöfer, Martin, Möller, Angela
• Format: Journal Article
• Language: English
• Published: United States 04.06.2018
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.8b00191

BaNa Fe[VO ] contains a Jahn-Teller active ion (Fe , 3d , 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 Fe . 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 E electronic state below 293 K, and finally the signature of the thermodynamically preferred orbitally nondegenerate ground state ( A ) 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.