Practical Electron Microscopy and Database

In some TM (transition metal) cases, the filling of orbitals with electrons may affect the local structure and thus induce geometrical distortion around the TM ion. The Jahn–Teller effect, also called Jahn–Teller distortion, describes this type of distortions. A typical Jahn-Teller ion is Mn³⁺ as shown in Figure 3133. The ion in the high-spin configuration contains a single electron in the upper e_g state when it is placed in an octahedral LF (ligand field). A tetragonal distortion can lower the energy of the system. The lowering in total energy is due to the lowering of one of the e_g orbitals by lengthening the bond along the z axis. Note that the overall energy of the system is not further lowered by splitting the t_2g state because the center of gravity is retained.