Structural commonalities of high-temperature superconductors

It is shown that all of the presently known high-temperature superconductors belong to one structural type with a basic cell of approximate 4/mmm,D _4h symmetry in tetragonal compounds andmmm,D _2h symmetry in orthorhombic compounds. In the Ba(Pb1–xBi _x )O₃ and YBa₂Cu₃O_7– compounds the basic cell is the unit cell and in the (La_1–x Sr _x )₂CuO₄, BiSrCaCuO and TIBaCaCuO compounds it is half the unit cell. The features of more than one copper oxide layer per basic cell, oxygen-free cation layers (e.g., Ca, Y) between CuO₂ layers, and slightly puckered CuO₂ planes seem to favor higher transition temperatures. The feasibility of several proposed or potentially superconducting structures are analyzed by this scheme.