perovskites and its effect on electronic properties*

The para-X phases (X=elastic, magnetic, and electric) of ABO₃ perovskites represent spatial configurations of microscopic degree-of-freedoms (m-DOFs), i.e., local dipole/magnetic-moment/distortion. In their simple representations, these m-DOFs are assumed to be zero and are allowed to be non-zero only due to thermal agitation. Here, by minimizing internal energy in a cubically shaped supercell, we find that a distribution of intrinsic m-DOFs exists even before temperature sets in, being a polymorphous network and forming a precursor of para-phase. In contrast, many cubic compounds are never polymorphous, being stable without symmetry breaking as in BaZrO₃. The formation of such distribution of m-DOFs leads to a change of electronic properties, such as mass-enhancement in paramagnetic SrVO₃, piezoelectricity in paraelectric BaTiO₃, and band gap opening in paraelastic BaBiO₃. Interestingly, these effects are obtained in symmetry-broken DFT without explicit strong correlation. Our findings provide a theoretical interpretation of spontaneous symmetry-breaking in cubic para-phases. We also find cases where multiple m-DOFs coexist in a single system, leading to a significant change of electronic properties as in NaNbO₃.