Since conduction electrons of a metal effectively screen the local electric dipole moments, it was widely believed that the ferroelectric- (FE-) like distortion cannot occur in metals. Recently, metallic ${\mathrm{LiOsO}}_3$ was discovered to be the first clear-cut example of an Anderson-Blount “ferroelectric” metal, which at 140 K undergoes a ferroelectriclike structural transition similar to insulating ${\mathrm{LiNbO}}_3$. This is very surprising because the mechanisms for structural phase transitions are usually quite distinct in metals and insulators. Through performing first-principles calculations, here we reveal that the local polar distortion in ${\mathrm{LiOsO}}_3$ is solely due to the instability of the $A$-site Li atom, in contrast to the ${\mathrm{LiNbO}}_3$ case where the second-order Jahn-Teller effect of the $B$-site Nb ion also plays an additional role. More importantly, the ferroelectriclike long-range order of the local polar distortion is found to be due to the predominantly ferroelectric short-range pair interactions between the local polar modes, which are not screened by conduction electrons. Furthermore, we predict that ${\mathrm{LiNbO}}_3$-type ${\mathrm{MgReO}}_3$ is also a ferroelectric metal but with a much higher structural transition temperature by 391 K than ${\mathrm{LiOsO}}_3$. Our paper not only unravels the origin of FE-like distortion in ${\mathrm{LiNbO}}_3$-type ferroelectric metals, but also provides a clue for designing other multifunctional ferroelectric metals.

• Received 21 March 2014
• Revised 22 August 2014

DOI:https://doi.org/10.1103/PhysRevB.90.094108