Tuning the orbital-lattice fluctuations in the mixed spin-dimer system Ba$_{3-x}$Sr$_{x}$Cr$_{2}$O$_{8}$

TL;DR

This study investigates how substituting Ba for Sr in Ba$_{3-x}$Sr$_{x}$Cr$_{2}$O$_{8}$ affects orbital-lattice fluctuations, revealing a suppression of these fluctuations with increased Ba content through diffraction, Raman, and calorimetry analyses.

Contribution

It demonstrates that Ba substitution suppresses orbital-lattice fluctuations in the mixed spin-dimer system, contrasting with linear changes in structural parameters.

Findings

Suppression of orbital-lattice fluctuation regime with more Ba

Contrasts with linear behavior of unit cell volume and atomic positions

Phonon frequency evolution indicates dynamic changes in lattice distortions

Abstract

In $A_{3}$Cr$_{2}$O$_{8}$, where $A$ = Sr or Ba, the Cr$^{5+}$ ions surrounded by oxygen ions in a tetrahedral coordination are Jahn-Teller active. The Jahn-Teller distortion leads to a structural transition and a related emergence of three twinned monoclinic domains below the structural phase transition. This transition is highly dynamic over an extended temperature range for $A$ = Sr. We have investigated mixed compounds Ba$_{3-x}$Sr$_{x}$Cr$_{2}$O$_{8}$ with $x=2.9$ and $x=2.8$ by means of X-ray and neutron diffraction, Raman scattering and calorimetry. Based on the obtained evolution of the phonon frequencies, we find a distinct suppression of the orbital-lattice fluctuation regime with increasing Ba content. This stands in contrast to the linear behaviour exhibited by unit cell volumes, atomic positions and intradimer spin-spin exchange interactions.