EPR study of the Jahn-Teller effect of Cu2+ in ZnTiF6·6H20
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The 34-GHz EPR spectrum of Cu2+ in ZnTiF6·6H20 shows a Jahn-Teller effect with a transition
from a single-line spectrum at high temperatures to a multiline anisotropic spectrum. The transition
temperature on cooling varied with Cu concentration from 172 K for a sample containing 0.2
at.% Cu to roughly 90 K for a 46-at. % Cu sample. For dilute samples, the single-line spectrum
was isotropic at 300 K with g =2.223±0.005, but showed axial symmetry about the trigonal axis at
180 K with gj1 =2.226±0.005 and g~ =2.223±0.005. At 4.2 K, a "static" Jahn-Teller effect was
observed with six axially symmetric Cu2+ spectra, each with g 11 =2.470±0.005, g1 =2.100±0.005,
I A 11 I ~ I 06 X 10- 4 em -I, and I A 1 I ~30 X 10- 4 em - I. The z axis of these spectra was found to lie
along the fourfold axes of two cubes with a common [Ill] axis, rotated by 40"±2" with respect to
each other about this axis. Analysis of the 4.2-K data leads to the values q~O. 50 for the Ham
reduction factor and K~O. 26 for the Fenni contact parameter, with A uA 1 < 0. An activation energy
of about 100 cm-1 was deduced from the gradual increase of the anisotropy of the spectrum on
cooling in the low-temperature region.
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QC Physics