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Schlagwörter:
Phase Transition; Angular Dependence; Order Transition; Temperature Phase; Order Phase Transition
Zusammenfassung:
The39K NMR spectra, spin-spin (T 2) and spin-lattice (T 1) relaxation times of KLiSO4 have been measured in the temperature range from 300 K to 90 K. The temperature dependence of the39K (I=3/2) NMR spectra demonstrates the occurrence of a first order phase transition atT c1=217 K which occurs without a change in the K+ site symmetry and another first order transition atT c2=190 K which is connected with a lowering of the K+ site symmetry and the formation of three kinds of ferroelastic domains. From the angular dependence of the second order quadrupole shifts of the39K NMR 1/2→−1/2 transitions the electric-field gradient (EFG) tensors at the potassium sites were determined at 290 K, 204 K and 180 K. The symmetry of the ferroelastic phase is monoclinic and not orthorhombic as the K+ EFG tensors are tilted away from thec-axis belowT c2. TheT 1 data further show the freezing in of the slow reorientational motion τ∼10−8 s with decreasing temperature from 300 to 90 K.
