Electromechanical properties of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mn>180</mml:mn> <mml:mo>∘</mml:mo> </mml:msup> </mml:math> domain wall in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msu

We analyze the electromechanical response of the <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:msup> <a:mn>180</a:mn> <a:mo>∘</a:mo> </a:msup> </a:math> ferroelectric domain wall in tetragonal <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:msub> <b:mi>PbTiO</b:mi> <b:mn>3</b:mn> </b:msub> </b:math> by combining first-principles calculations with a Landau-Ginzburg-Devonshire (LGD) description. Using regular multidomain structures with varying domain-wall density, we extract polarization profiles and lattice distortions and map them onto the continuum model to determine conventional (homogeneous) and gradient (inhomogeneous) electrostriction. Conventional electrostriction yields only a small negative length change of the sample, whereas gradient electrostriction—arising from the coupling between strain and polarization gradients—produces a positive contribution nearly an order of magnitude larger and localized at the wall core. Our results demonstrate that gradient electrostriction dominates the electromechanical response of <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:msup> <c:mn>180</c:mn> <c:mo>∘</c:mo> </c:msup> </c:math> walls in <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"> <d:msub> <d:mi>PbTiO</d:mi> <d:mn>3</d:mn> </d:msub> </d:math> , supporting its inclusion in LGD models that stabilize Bloch-type domain wall structures.