Continuous crossover between insulating ferroelectrics and polar metals: extit{Ab initio} calculation of structural phase transitions of Li$B$O$_3$ ($B$ = Nb, Ta, W, Re, Os)*

We investigate the polar-nonpolar structural phase transition of LiBO3 with B = Nb, Ta, W, Re, Os from first principles. We calculate the temperature dependence of the crystal structures using the structural optimization based on the self-consistent phonon (SCPH) theory[1,2], which accurately reproduces the chemical trend of the transition temperatures. Combining with the calculations of the electronic structures and harmonic phonon dispersions, we predict that LiWO3 is a polar metal yet to be tested experimentally.

Upon doping electrons to the insulating LiTaO3, the predicted transition temperature is quickly suppressed and approaches those of the polar metals. Thus, there is a continuous crossover between insulating ferroelectrics and polar metals through doped ferroelectrics. Looking into the detailed structures of the interatomic force constants, we find clear evidence that the suppression of the transition temperatures in the polar metals can be ascribed to the screening of the long-range Coulomb interaction, which is caused by the presence of the itinerant electrons [3].

 

[1] D. J. Hooton, Phil. Mag. 3, 49 (1958). 

[1] R. Masuki, T. Nomoto, R. Arita, T. Tadano, Phys. Rev. B 106, 224104 (2022).

[2] R. Masuki, T. Nomoto, R. Arita, T. Tadano, in preparation.