Emergent ferroelectric order in strained KTaO 3 by anharmonic and machine learned force fields methods

Ferroelectric materials are a class of dielectrics that exhibit spontaneous polarization which can be reversed under an external electric field. The emergence of ferroelectric order in incipient ferroelectrics is a topic of considerable interest from both fundamental and applied perspectives. Despite evidence from first-principles calculations that strain triggers ferroelectricity in <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:msub> <a:mi>KTaO</a:mi> <a:mn>3</a:mn> </a:msub> </a:math> , conventional methods cannot reliably characterize the soft-mode dynamics that govern its ferroelectric behavior. In this study, we investigate the impact of in-plane uniaxial and biaxial strain, ranging from 0 to 1%, on pristine <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:msub> <b:mi>KTaO</b:mi> <b:mn>3</b:mn> </b:msub> </b:math> to explore its potential for ferroelectricity induction via inversion symmetry breaking. By integrating density-functional theory calculations with the stochastic self-consistent harmonic approximation assisted by on-the-fly machine learned force fields, we obtain accurate structural information and dynamical properties under varying strain conditions while incorporating higher-order anharmonic effects. Employing the Berry-phase method, we obtained the ferroelectric polarization of the strained structures over the entire temperature range up to 300 K. Our findings provide valuable insights into the role of strain in stabilizing ferroelectricity in <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:msub> <c:mi>KTaO</c:mi> <c:mn>3</c:mn> </c:msub> </c:math> , offering guidance for future experimental and theoretical studies on strain-engineered ferroelectric materials.