ISSN:
1432-0630
Keywords:
77.40
;
61.70
;
66.30
Source:
Springer Online Journal Archives 1860-2000
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Physics
Notes:
Abstract The fluorides of the rutile structure are relatively simple ionic materials with tetragonal symmetry for which the dominant intrinsic defect has not been established. The present experiments involve low-temperature dielectric relaxation measurements on Er3+-and Y3+-doped MnF2 single crystals. Unexpectedly, dielectric loss peaks were observed at cryogenic temperatures, involving very low activation energies,E. For both dopants a prominent peak is observed for samples oriented parallel to thec-axis withE ∼ 6 meV and in perpendicular orientations withE=37 meV for Er3+ and 46 meV for Y3+ doping. Such lowE-values are probably too small to be controlled by lattice migration of a defect. Rather, we expect that they are due to a very low symmetry configuration created when the ions near the defect move “off symmetry” to a more stable configuration. Computer simulation calculations have been carried out which are much improved over early studies of this system in terms of the code used and the F-F interatomic potentials. The results show that the energy per defect for the anion Frenkel (1.53 eV) is lower than that of the Schottky (1.99 eV). It was also shown that the fluorine interstitial, Fi, adopts a split-interstitial form. This defect associates strongly with trivalent dopants Er and Y to produce a low symmetry dipolar structure with the necessary off-symmetry configuration to explain the experimental findings. Since there is no alternative way to explain these low temperature relaxations in terms of impurities associated with Mn vacancies, as would be required by the Schottky model, we conclude that these experiments serve to establish the nature of the intrinsic defect in MnF2 as anion Frenkel.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00615467
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