  Metals cannot exhibit ferroelectricity because static internal electric
fields are screened by conduction electrons, but in 1965, Anderson and Blount
predicted the possibility of a ferroelectric metal, in which a
ferroelectric-like structural transition occurs in the metallic state. Up to
now, no clear example of such a material has been identified. Here we report on
a centrosymmetric (R-3c) to non-centrosymmetric (R3c) transition in metallic
LiOsO3 that is structurally equivalent to the ferroelectric transition of
LiNbO3. The transition involves a continuous shift in the mean position of Li+
ions on cooling below 140K. Its discovery realizes the scenario described by
Anderson and Blount, and establishes a new class of materials whose properties
may differ from those of normal metals.
