Varizonicity and surface levels in ionic crystals

The problem of the formation of varizonicity in ionic crystals is investigated. It is shown that in this case the electronic structure of the surface states becomes special – a near-surface potential well appears, as a result of which the local states radically differ from the Tammov states. A similar effect, in principle, should take place in cases of varizonicity of covalent crystals, which is due to special alloying in them. A consideration is made about the special situation in HTS materials: a combination of external and internal varizonality.