The results of the study of donor negative U centers in lead chalcogenides by Mössbauer emission spectroscopy are discussed. The published data regarding the identification of amphoteric negative U centers in glassy binary arsenic and germanium chalcogenides using Mössbauer emission spectroscopy, and in multicomponent chalcogenide glasses using Mössbauer absorption spectroscopy are considered. Published data concerning the identification of two-atom negative U centers in lattices of the metal-oxides of copper by Mössbauer emission spectroscopy are analyzed. The principal possibility of using Mössbauer negative U centers as a tool for studying the Bose ¿ Einstein condensation of electron pairs during the superconducting phase transition in high-temperature and classic superconductors is considered.
