Pressure-induced phase transition and phonon softening in h−Lu0.6Sc0.4FeO3

We combine diamond anvil cell techniques, synchrotron-based infrared and Raman scattering spectroscopies, a symmetry analysis, and complementary lattice dynamics calculations to explore the pressure-driven phase transition in multiferroic $h\text{\ensuremath{-}}{\mathrm{Lu}}_{0.6}{\mathrm{Sc}}_{0.4}{\mathrm{FeO}}_{3}$. Comparison of the measured and predicted phonon patterns reveals a $P{6}_{3}cm\ensuremath{\rightarrow}P\overline{3}c1$ structural transition at 15 GPa. Symmetry breaking across the polar $\ensuremath{\rightarrow}$ antipolar transition takes place via changes in the bipyramidal tilting direction and Lu/Sc displacement pattern, analogous to the strain-driven ${K}_{3}$ distortion pathway in $h\text{\ensuremath{-}}{\mathrm{LuFeO}}_{3}$ and temperature-induced transitions in the rare-earth manganites.