39K NMR-STUDY OF THE PARAELECTRIC-TO-INCOMMENSURATE PHASE-TRANSITION IN K2ZNCL4

The temperature dependence of the quadrupole-perturbed K-39 1/2 --> -1/2 NMR line shapes has been measured in the paraelectric (PE), incommensurate (I), and commensurate (C) phases of K2ZnCl4 between 600 and 390 K. In the PE phase and the high-temperature part of the I phase, fast chemical exchange of the 39K nuclei as well as a diffusive floating of the incommensurate modulation wave take place. In the low-temperature part of the I phase the modulation wave becomes solitonlike. The soliton density does not vanish as the I-C transition but persists well into the C phase.