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.