  The empirical relation of T_co(K)=2740/<q>_c^4 between the transition
temperature of optimum doped superconductors T_co and the mean cationic charge
<q>_c, a physical paradox, can be recast to strongly support fractal theories
of high-T_c superconductors, thereby applying the finding that the optimum hole
concentration of h^+ = 0.229 can be linked with the universal fractal constant
delta_1 = 8.72109... of the renormalized Henon map. The transition temperature
obviously increases steeply with a domain structure of ever narrower size,
characterized by Fibonacci numbers. With this backing superconductivity above
room temperature can be conceived for synthetic sandwich structures of <q>_c
less than 2+. For instance, composites of tenorite and cuprite respectively
tenorite and CuI (CuBr, CuCl) onto AuCu alloys are proposed. This specification
is suggested by previously described filamentary superconductivity of 'bulk'
CuO_1-x samples. In addition, cesium substitution in the Tl-1223 compound is an
option. A low mean cationic charge allows the development of a frustrated
nano-sized fractal structure of possible ferroelastic nature delivering
nano-channels for the very fast charge transport, in common for both high-T_c
superconductors and organic inorganic halide perovskite solar materials.
