Pressure effects on Jahn-Teller distortion in perovskites: The roles of local and bulk compressibilities

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The interplay between the Jahn-Teller (JT) effect and octahedron tilting in transition-metal perovskites is investigated as a function of pressure. Our focus is on its effects on the exchange and electron-phonon interactions, both having a strong influence on materials properties. We demonstrate that the JT distortion in Cu${}^{2+}$ and Mn${}^{3+}$ is reduced upon compression and is eventually suppressed at pressures above 20 GPa. X-ray diffraction and x-ray absorption measurements in ${A}_{2}{\text{CuCl}}_{4}$ layer perovskites ($A$: Rb, C${}_{n}$H${}_{2n+1}$NH${}_{3}$; $n=1$--3) show that, although pressure slightly reduces the long Cu-Cl distance in comparison to the Cu-Cu distance in the layer, the JT distortion is stable in the 0--20 GPa range. The difference between lattice (${\ensuremath{\beta}}_{0}^{C}=0.14$ GPa${}^{\ensuremath{-}1}$) and local CuCl${}_{6}$ (${\ensuremath{\beta}}_{0}=0.016$ GPa${}^{\ensuremath{-}1}$) compressibilities, together with the high stability of the JT distortion, lead to ${\mathrm{CuCl}}_{6}$ tilts upon compression. The evolution of the elongated CuCl${}_{6}$ octahedron in ${A}_{2}$CuCl${}_{4}$, as well as MnF${}_{6}$ in CsMnF${}_{4}$ and MnO${}_{6}$ in LaMnO${}_{3}$ and DyMnO${}_{3}$, toward a nearly regular octahedron takes place above 20 GPa, in agreement with experimental results and a model analysis based on the JT energy derived from optical absorption spectroscopy: ${E}_{\mathrm{JT}}=0.25$--0.45 eV/Cu${}^{2+}$, ${E}_{\mathrm{JT}}=0.45$ eV/Mn${}^{3+}$ (CsMnF${}_{4}$), and ${E}_{\mathrm{JT}}=0.25$ eV/Mn${}^{3+}$ (LaMnO${}_{3}$). The proposed model clarifies controversial results about pressure-induced JT quenching in Cu${}^{2+}$ and Mn${}^{3+}$ systems, providing an efficient complementary means to predict pressure behavior in perovskites containing JT transition-metal ions.