Comment on "Molecular structure and dynamics of off-center Cu(2+) ions and strongly coupled Cu(2+)-Cu(2+) pairs in BaF(2) crystals: Electron paramagnetic resonance and electron spin relaxation studies" [J. Chem. Phys. 127, 124705 (2007)].
In the recent study of Cu(2+)-doped BaF(2) Hoffmann et al. demonstrated using electron paramagnetic resonance spectroscopy that the Cu(2+) impurity experiences an off-center shift from the substitutional position and ascribe this distortion to the Jahn-Teller effect. In this comment, we propose that the off-center distortion observed for BaF(2):Cu(2+) is driven by pseudo-Jahn-Teller interactions which are qualitatively different and in competition with the usual Jahn-Teller effect. It is also stressed that off-center phenomena in a given host lattice are not necessarily enhanced by decreasing the ionic radius of the impurity.
García-Fernández
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Departamento de Ciencias de la Tierra y Fisica de la Materia Condensada, Avda. de los Castros s/n, 39005 Santander, Spain. garciapa@unican.es
Aramburu
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Moreno
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Barriuso
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