Nuclear quadrupole resonance study of phase transitions and incommensurability in K2SbF5

Phase transitions and incommensurability in K2SbF5 has been studied by means of 123Sb NQR spectra and spin-lattice relaxation measurements. The phase transitions have been obtained at 117, 135 and 260 K. Line shape and temperature dependence of the spin-lattice relaxation time T1 in the temperature range from 135 to 260 K are characteristic for the incommensurate state with the plane wave modulation regime. At 117 to 135 K, a distinct fine structure of NQR spectra has been observed. Redistribution of line intensities with the variation of temperature allows us to suggest that this phase exhibits domain structure, and that one of the domains becomes energetically beneficial on cooling and transforms into the low temperature phase at 117 K. The 123Sb NQR measurements in K2SbF5 show unusually short values of T1, which become close to the spin-spin relaxation time T2 with increasing temperature. (author)