  A novel stable crystallographic structure is discovered in a variety of ABO3,
ABF3 and A2O3 compounds (including materials of geological relevance,
prototypes of multiferroics, exhibiting strong spin-orbit effects, etc...), via
the use of first principles. This novel structure appears under hydrostatic
pressure, and is the first "post-post-perovskite" phase to be found. It
provides a successful solution to experimental puzzles in important systems,
and is characterized by one-dimensional chains linked by group of two via
edge-sharing oxygen/fluorine octahedra. Such unprecedented organization
automatically results in anisotropic elastic properties and new magnetic
arrangements. Depending on the system of choice, this post-post-perovskite
structure also possesses electronic band gaps ranging from zero to ~ 10 eV
being direct or indirect in nature, which emphasizes its "universality" and its
potential to have striking, e.g., electrical or transport phenomena.
