HTSCS WITH APICAL OXYGEN REPLACED BY HALOGEN

The fundamental structural unity of familiar oxide HTSCs and their oxy haloide counterparts, with apical oxygen ions replaced by halogen ions , is demonstrated and discussed. As a consequence of this unity, major physical phenomena are expected to be common for both classes, such a s doping effects, concentration-driven insulator-metal transitions, th e unusual pair superconductivity, and the temperature dependence anoma lies in the critical magnetic field, linear expansion coefficient, and heat capacity jumps. New experimental results are discussed, accounte d for by the exciton mechanism of superconductivity with the local nat ure of excitations taken into account.