Abstract
Raman spectroscopy experiments on single crystals of and 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 and tetragonal phases at K is manifested in our spectra by a “repulsion” of two accidentally quasidegenerate symmetric modes below , caused by a phonon mixing effect that is only operative in the monoclinic phase due to symmetry restrictions. Also, two specific phonons, associated with octahedra rotation and with a Jahn-Teller elongation mode, soften and broaden appreciably as . A crossover from a displacive to an order-disorder transition at is inferred.
2 More- Received 31 January 2018
DOI:https://doi.org/10.1103/PhysRevB.97.104304
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