Ferroelastic phase transition and twin structure by Cs-133 NMR in a CsPbCl3 single crystal

The temperature dependence of the Cs-133 nuclear magnetic resonance (NMR) i n a ferroelastic CsPbCl3 single crystal has been investigated using a FT NM R spectrometer. The rotation patterns of the, Cs-133 NMR spectra were obtai ned in three mutually perpendicular planes under an applied magnetic field of 9.4T. Two sets of seven-line structures were obtained instead of a simpl e seven-line structure of the Cs-133(I = 7/2) nucleus in CsPbCl3 crystal. F rom these results, the NMR parameters were obtained. These showed the same magnitudes of quadrupole coupling constants and asymmetry parameters for re sonance lines of the two sets. but with different orientations. It is known that two different orientations in phases II-IV occurred in ferroelastic d omains. The domain wall makes an angle of 45 degrees with respect to the [1 0 0] axis in phases II-IV. At the transition point of 47 degreesC, one sig nal from the Cs-133 resonance line indicates that a phase transition takes place to a new phase with higher symmetry than tetragonal. There is no EFG tensor at the Cs site in phase 1. The parameters obtained from the Cs-133 N MR spectra were based on the occurrence of first-order phase transitions at 37 degreesC and 47 degreesC, and a second-order phase transition at 42 deg reesC. (C) 2001 Elsevier Science B.V. All rights reserved.