Figure 1

NPD diagrams for ambient temperature and 800 K, fitted to the model described in the text in the I4/mcm space group. Observed (circles), calculated (full line), and difference (down) profiles, with the allowed Bragg reflections as vertical marks.Reuse & Permissions

Figure 2

(i) Temperature dependence of the lattice parameters of LaMnO${}_3$ through the cJT transition temperature $T_{\mathrm{JT}}$ ∼ 750 K from Ref. 24. (ii) Temperature dependence of the primary cell lattice parameters of KCrF${}_3$[24] and KCuF${}_3$ through their expected JT distortions. The error bars are smaller than the symbols. Structural phase transitions are usually preceded by a deviation from the cell parameters trend line, as seen with LaMnO${}_3$;[25] however, no such deviation is observed for KCrF${}_3$ until the lattice parameters collapse to pseudocubic at $T_{\mathrm{JT}}\sim 970$ K. The JT distortion increases with temperature for KCuF${}_3$ through 900 K, with no indication of the occurrence of a structural phase transition before its decomposition.Reuse & Permissions

Figure 3

The pressure and temperature dependence of the bonds in the MnO${}_6$,[25, 28] CrF${}_6$,[24] and CuF${}_6$ octahedra from Ref. 19 and this work. The error bars are smaller than the symbols. LaMnO${}_3$ and KCrF${}_3$ show a collapse of their long, medium and short bonds into degenerate lengths after passing through their $T_{\mathrm{JT}}$ at 750 and 970 K, respectively. KCuF${}_3$ shows no indication of this through the expected Jahn-Teller distortion onset temperature $T_{\mathrm{JT}}$ ∼ 800 K. Under high pressure, the JT distortion of both LaMnO${}_3$ and KCuF${}_3$ is suppressed.Reuse & Permissions

Figure 4

A quarter of the polar plot of the site distortion of KCuF${}_3$, KCrF${}_3$, and LaMnO${}_3$ as a function of temperature, pressure, and dilution by non-JT ions. Data in this plot are from this work and Refs. 19, 26, 25, 29, 27, 24 in the order they appear. Arrows inside the figure point to directions of increasing temperature, pressure, or concentration of non-JT ions in different JT systems.Reuse & Permissions