A predictive bond order model connects covalent superconductivity,   including cuprates, oxypnictides or HfN based materials
  A phenomenological bond order model predicting doping curves [Tc vs doped charge, c] of cuprates is found to have wider applicability. In this model Tc is dependent on the density of electronic pair crystals [EC] in a covalently bonding layer structure and on a layer Isolation factor, f [ECI model]. Characteristic doping curve events such as optima are correlated with a select number of EC with pair repeats corresponding to multiples of lattice parameters such as c=2/3x4=0.167, where 3x4 represent pair periodicity of 3a0 and 4b0. At these EC all doped charge is converted into pairs according to c=2np. For Tc prediction one writes Tc=2npfTe, where Te=600K and 300K as empirical constants for hole and electron doping. Doping curves for YBa2Cu3Oy with their sharp optima or kinks, separated by near linear ranges, or Tc plateaus on different preparations, can express the stability of special EC. Examples are c=0.22=2/32 for the sharp optimum or the Tc=90K plateau, and c= 0.17 for the 60K plateau, the latter depicting also the optimum for other systems such as La2-wSrwCuO4. For oxypnictides R[O1-xFx]FeAs one writes Tc=300x and expects EC with optimal dopings at x=0.11 and 0.17, as corroborated experimentally. Other examples include HfN derivatives such as Li0.17HfNCl. 
H. Oesterreicher