2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/228833Inelastic 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.17 pages, 5 figures Revised version; final versionStrongly Correlated ElectronsPattern Formation and Solitonstext