Hard antiphase domain boundaries in strontium titanate: A comparison of Landau-Ginzburg-Devonshire and ab initio results

Recently, the emergence of polarity of so-called hard antiphase boundaries in strontium titanate was investigated using atomistic simulations based on machine-learned force fields. Comparing the resulting order parameter (OP) and polarization profiles to those obtained from numerical solutions based on a well-established Landau-Ginzburg-Devonshire (LGD) parametrization produces good agreement of the structural OP amplitudes but fails dramatically in reproducing the shape and pressure behavior of the domain wall (DW) polarization. While the atomistic simulations yield a nonzero DW polarization up to at least 120 kbar, LGD theory would predict a sharp transition to zero at a pressure as low as 4.6 kbar. A semiquantitative agreement can be restored by adding so-called rotopolar couplings to the LGD potential and by considering the effects of nuclear quantum fluctuations. Additional evidence for the correctness of our extensions of the LGD approach is provided by comparing the temperature dependence of the DW polarization to recent experimental depolarization pyrocurrent measurements. Our results illustrate the importance of accounting for nuclear quantum effects beyond standard atomistic approaches in the investigation of DW properties.

Automated summary

This study investigates the emergence of polarity in so-called hard antiphase boundaries in strontium titanate using atomistic simulations and numerical solutions. Traditional numerical solutions fail to reproduce the shape and pressure behavior of the domain wall polarization, but adding rotopolar couplings and considering nuclear quantum fluctuations can restore semiquantitative agreement.