Ferroelastic phase transition and twin structure by 133Cs NMR in a CsPbCl 3 single crystal

Abstract

The temperature dependence of the 133Cs nuclear magnetic resonance (NMR) in a ferroelastic CsPbCl 3 single crystal has been investigated using a FT NMR spectrometer. The rotation patterns of the 133Cs NMR spectra were obtained in three mutually perpendicular planes under an applied magnetic field of 9.4 T. Two sets of seven-line structures were obtained instead of a simple seven-line structure of the 133Cs( I= 7 2 ) nucleus in CsPbCl 3 crystal. From these results, the NMR parameters were obtained. These showed the same magnitudes of quadrupole coupling constants and asymmetry parameters for resonance lines of the two sets, but with different orientations. It is known that two different orientations in phases II–IV occurred in ferroelastic domains. The domain wall makes an angle of 45° with respect to the [1 0 0] axis in phases II–IV. At the transition point of 47°C, one signal from the 133Cs 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 I. The parameters obtained from the 133Cs NMR spectra were based on the occurrence of first-order phase transitions at 37°C and 47°C, and a second-order phase transition at 42°C.