Suppression of the cooperative Jahn-Teller distortion and its effect on the Raman octahedra-rotation modes of TbMn1−xFexO3

This work reports the changes in structure and lattice dynamics induced by substituting the Jahn-Teller-active $\mathrm{M}{\mathrm{n}}³⁺$ ion by the Jahn-Teller-inactive $\mathrm{F}{\mathrm{e}}³⁺$ in $\mathrm{TbM}{\mathrm{n}}_{1\text{\ensuremath{-}}x}\mathrm{F}{\mathrm{e}}_x{\mathrm{O}}₃$ over the full composition range. The structural analysis reveals that the amplitude of the cooperative Jahn-Teller distortion decreases linearly from $x=0$ (pure $\mathrm{TbMn}{\mathrm{O}}₃)$ to $x=0.5$, where it is completely suppressed. We then correlate this evolution with the behavior of the Raman modes across the solid solution. In particular, we show that the Raman modes associated with the rotation of octahedra, whose wave number is commonly considered to scale linearly with the tilt angles in orthorhombic Pnma perovskites, are also sensitive to the amplitude of the Jahn-Teller distortion.