Screw- Type Motion and Its Impact on Cooperativity in BaNa₂Fe[VO₄]₂

Area of Science:

• Solid State Chemistry
• Materials Science
• Crystallography

Background:

• BaNa2Fe[VO4]2 features a Jahn-Teller active Fe(II) ion in octahedral coordination.
• Understanding electron-lattice coupling is crucial for materials with complex electronic states.

Purpose of the Study:

• To investigate the structural phase transition in BaNa2Fe[VO4]2.
• To elucidate the coupling between lattice dynamics and the electronic ground state of Fe(II).

Main Methods:

• Temperature-dependent X-ray diffraction.
• Mössbauer spectroscopy.
• Raman spectroscopy.

Main Results:

• A structural transition around room temperature is driven by coupled lattice modes affecting Fe(II).
• Mössbauer data show distinct electronic state evolutions of Fe(II) with temperature (motion-narrowed doublet, 5Eg, and 5Ag states).
• Raman spectroscopy reveals temperature-dependent phonon parameters indicating strong electron-phonon coupling.

Conclusions:

• A microscopic mechanism for the collective structural phase transition driven by electron-phonon coupling is presented.
• The study highlights the interplay between electronic and lattice degrees of freedom in BaNa2Fe[VO4]2.