Intrinsic Localized Modes Observed in the High Temperature Vibrational   Spectrum of NaI
  Inelastic neutron measurements of the high-temperature lattice excitations in NaI show that in thermal equilibrium at 555 K an intrinsic mode, localized in three dimensions, occurs at a single frequency near the center of the spectral phonon gap, polarized along [111]. At higher temperatures the intrinsic localized mode gains intensity. Higher energy inelastic neutron and x-ray scattering measurements on a room-temperature NaI crystal indicate that the creation energy of the ground state of the intrinsic localized mode is 299 meV. 
M. E. Manley, A. J. Sievers, J. W. Lynn, S. A. Kiselev, N. I. Agladze,   Y. Chen, A. Llobet, A. Alatas