Compositions in YBa2Cu3Oy for 3-D bond order superconductors
  Self-doping in YBa2Cu3Oy starts to switch from a charge balancing of chain metal reduction and plane oxidation to one of chain ligand oxidation (O-) and plane reduction on quenching from >600K. Amongst the responses are plane expansions and types of unusually strong superconductivity such as elevated temperature superconductivity (ETS), observed through laser pulsing (Tc=552K*) and upon shot quenching (Tc=200K*). We ascribe ETS to limited 3-D superconductivity due to a correlated system of bond ordering within chain-plane sandwiches and propose how to stabilize it. Accordingly, plane expanding n-doping arises from self-doping charge equilibration with local chain Cu of two-fold O coordination (2). The dumbbell type bonds of both apical O- are a result of high-energy environment and comparable in their metric with electron pairs on the plane. Following empirical Tc=%(2)x11 we suggest increasing %(2) to cause the observed retrograde rise in Tc (photo-induced reflectivity edge) to a theoretical limit of Tc=1100K* at 100%(2). We propose compositions and heat treatments based on charge-lattice commensurability. Paired charge concentrations on planes, determined by bond ordering based on magic number counts, suggest several promising candidates such as c=0.22=2/3a0x3b0, c=0.17=2/3x4 or c=0.080=2/5x5. The latter could be achieved with 32%(2) and display Tc=352K* not only in laser pulsed but in shot quenched materials. 
H. Oesterreicher (Department of Chemistry, UCSD)
cond-mat.mtrl-sci