Lattice dynamics of ASb2O6 (A=Cu,Co) with trirutile structure

TL;DR

This study investigates the lattice dynamics of ASb2O6 (A=Cu,Co) with trirutile structure using Raman spectroscopy and ab-initio calculations, revealing a structural transition at 400 K and phonon behavior related to phase change.

Contribution

It provides the first detailed Raman and lattice dynamics analysis of ASb2O6 compounds, identifying phonon modes and the nature of the phase transition at 400 K.

Findings

Identification of Raman-active phonon modes in CuSb2O6 and CoSb2O6.

Observation of phonon mode repulsion below 400 K indicating a structural transition.

Evidence of a crossover from displacive to order-disorder transition at Ts.

Abstract

Raman spectroscopy experiments on single crystals of CuSb2O6 and CoSb2O6 quasi-one-dimensional antiferromagnets with trirutile crystal structure were performed, with a focus on the first material. The observed Raman-active phonon modes and previously reported infrared-active modes were identified with the aid of ab-initio lattice dynamics calculations. The structural transition between monoclinic beta-CuSb2O6 and tetragonal alpha-CuSb2O6 phases at Ts=400 K is manifested in our spectra by a "repulsion" of two accidentally quasi-degenerate symmetric modes below Ts, caused by a phonon mixing effect that is only operative in the monoclinic beta-CuSb2O6 phase due to symmetry restrictions. Also, two specific phonons, associated with CuO6 octahedra rotation and with a Jahn-Teller elongation mode, soften and broaden appreciably as T -> Ts. A crossover from a displacive to an order-disorder transition at Ts is inferred.