TY - JOUR AU - Stupka, A. A. PY - 2018/10/24 Y2 - 2024/03/29 TI - Frequencies of Long-Wave Phonon-Polaritons and Optical Phonons in Diatomic Ionic Crystals JF - Ukrainian Journal of Physics JA - Ukr. J. Phys. VL - 59 IS - 8 SE - Solid matter DO - 10.15407/ujpe59.08.0793 UR - https://ujp.bitp.kiev.ua/index.php/ujp/article/view/2018512 SP - 793 AB - <p>Long-wave phonon-polaritons and longitudinal optical phonons in ionic crystals with two atoms per unit cell have been considered. The model of the point charge and the self-consistent electromagnetic field in the dielectric medium is used. The standard dispersion laws for both branches of phonon-polaritons regarded as transversal waves are obtained. The frequency of longitudinal optical phonons is expressed in terms of the ion plasma frequency in an insulator multiplied by the factor √︀ ER -