Detection of the prototype symmetry of ferroelastic WO3 domain walls by angle-resolved polarized Raman spectroscopy

The symmetry of a domain wall in ferroelastic ${\mathrm{WO}}₃$ is analyzed by angle-resolved polarized Raman spectroscopy. We find that a low-energy Raman mode at $46\phantom{\rule{0.28em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1}$ is largely enhanced within the confined region of the domain wall, whose width is presumed to be $\ensuremath{\sim}25\phantom{\rule{0.28em}{0ex}}\mathrm{nm}$ from diffusive x-ray scattering. The wall effect on the enhancement of the Raman signal per unit area is estimated to be three times larger than the contribution of the domains. The light-polarization-dependent Raman intensity at the wall is characterized by the symmetric ${A}_1g$ Raman tensor that is attributed to the prototypic quasitetragonal phase imposed by the ferroelastic compatibility relationship.