Nuclear quadrupole resonance study of phase transitions and incommensurability in K2SbF5

Phase transitions and incommensurability in K2SbF5 has been studied by mean s of Sb-123 NQR spectra and spin-lattice relaxation measurements. The phase transitions have been obtained at 117, 135 and 260 K. Line shape and tempe rature dependence of the spin-lattice relaxation time T-1 in the temperatur e range from 135 to 260 K are characteristic for the incommensurate state w ith the plane wave modulation regime. At 117 to 135 K, a distinct fine stru cture of NQR spectra has been observed. Redistribution of line intensities with the variation of temperature allows us to suggest that this phase exhi bits domain structure, and that one of the domains becomes energetically be neficial on cooling and transforms into the low temperature phase at 117 K. The Sb-123 NQR measurements in K2SbF5 show unusually short values of T-1, which become close to the spin-spin relaxation time T-2 With increasing tem perature.