Search for new superconducting systems related to the infinite-layer family compounds: Normal pressure synthesis and the role of doping

The usual scheme of two different block layer intergrowth in order to describe high-Tc superconducting ceramics as modified to a three block layer scheme is reviewed. Based on this model, we remind the influence of bond mismatches, as the chemical causes for stress in the materials, on structural phase transition. From such a point of view, we discuss the result of ion insertion into the layers at ambient pressure and their consequence on p- or n-type superconductivity, or the absence of any superconducting phase. The role of the apical oxygen for charge-transfer through stress relief is pointed out as the likely chemical key ingredient for p-type superconductivity.