title: An electron paramagnetic resonance study of the tetragonally distorted [Formula: see text] ion in [Formula: see text] and [Formula: see text].
abstract: Chromium-doped [Formula: see text] and [Formula: see text] have been studied by both EPR and ENDOR spectroscopy. [Formula: see text] ions enter the fluorite structure in distorted substitution cation sites. In both matrices the distortion observed is tetragonal. X- and Q-band EPR measurements at temperatures between 4 and 300 K allowed us to determine the ion symmetry and the following spin-Hamiltonian parameters: [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] for [Formula: see text]; and [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] for [Formula: see text]. For [Formula: see text], the weak superhyperfine interaction of [Formula: see text] with the surrounding [Formula: see text] ions has been studied by both EPR and ENDOR techniques for [Formula: see text]. No ENDOR signals were detected for [Formula: see text]. The results are tentatively explained in terms of a Jahn - Teller effect corresponding to [Formula: see text] coupling strongly stabilized by lattice stresses, although other possible origins for the distortion cannot be completely ruled out.
authors.affiliation: Instituto de Ciencia de Materiales de Aragón, Universidad de Zaragoza - Consejo Superior de Investigaciones Científicas, Plaza San Francisco s/n, E-50009 Zaragoza, Spain.
authors.forename: P B
authors.initials: PB
authors.lastname: Oliete
authors.forename: V M
authors.initials: VM
authors.lastname: Orera
authors.forename: P J
authors.initials: PJ
authors.lastname: Alonso