New cell volume expanded, elevated temperature orthorhombics YBa2Cu3O6.5 and their Tc∝50 K plateau on time dependent transitions to volume contracted orthorhombics at room temperature

A range of strongly cell volume (V) expanded orthorhombics YBa2Cu3Oy, diagnosed as partly based on three fold O coordination of Cu(1), is found to be stable for y=6.5 when fast quenched from near 670 K. These materials can rapidly transform, presumably in a series of infinitely adaptable ladder structures, to more V contracted orthorhombics at lower T and constant y=6.5. The transformation rates (of order h) can be slowed by partial Ni substitutions. A Tc∝50 K plateau extends from V=173.0 to 174.8 A3, is followed by Tc collapse, but Tc can reappear with roughly doubled values (extrapolated) for the highest V (>176 A3) obtained by a different method. The cell volume expanded varieties suggest a new paradigm for massive selfdoping involving Cu+ and O-. This massive selfdoping is held responsible for Tc plateaus and also for strong Tc of complex cuprates such as Bi2Sr2Can-1CunO2n+4 or HgBa2CuO4. The new concepts have far ranging implications for existing literature on physical properties or questions of doping, charge transfer or lattice gas calculations. They support a subperoxide-metal adduct state model for superconductivity. (orig.)