Jahn-Teller ordering

The 1-D antiferromagnetic properties of KCuF3, although unexpected at first sight from a crystallographic point of view, can nonetheless be easily explained on the basis of Jahn-Teller ordering (Sect. 3.1.1). 

Fig. 52. Deformation stabilization of a tetragonal interstice, (a) Spin-orbit ordering given one h0 electron or Jahn-Teller ordering given two Ug electrons, (b) Jahn-Teller ordering given one ti0 electron or spin-orbit ordering given two tig electrons.

Fig. 53. Tetrahedral-site distortions due to ordering of a single electron. (Ordering of a single hole gives distortions of opposite sign.) (a) Jahn-Teller ordering into a drv orbital, (b) Spin-orbit ordering into the (dyz db idtx) orbitals.

Jahn-Teller ordering at Cu2+ distorts antiferromagnetic CuF2 similarly to CrF2 (70a). The unpaired dxt-y electron spins are presumably coupled via the shorter 135° cation-anion-cation links. 

Jahn-Teller effect above TV, there is no large exchange striction at TV. Note that the sign of the distortions (c/a < 1 vs. c/a > 1) to be associated with Jahn-Teller ordering of eg electrons depends upon second-order effects, which may explain why MnAu sometimes has c/a > 1. 

Figure 28 (a) Cs2NaAl3Fi2 type. Large spheres Cs, small spheres Na (b) Jahn-Teller ordering in A2A Mn3pi2 compounds... 

The lowest curve corresponds to the lowest temperature T = 0.1 (the magnetic field is much smaller than the Jahn-Teller ordering molecular field). If the molecular field is much smaller than Zeeman interaction the metamagnetoelastic jump disappears. 

How will the distorted octahedra arrange with respect to each other in a crystal stmcture of a certain symmetry, and vdiich are the most common geometric patterns of cooperative Jahn-Teller ordering ... 

Experimental data with respect to cooperative Jahn-Teller ordering in perovskite and elpasolite compounds as well as in lattices with isolated octahedra are collected in Table 2 for transition metal ions with electronic Eg ground states. The most inter-Chaps. II and III can be summarized as follows ... 

Table 2. Structural and spectroscopic data of representative examples with different types of Jahn-Teller ordering [abbreviations f fenodistortive, af = antifenodistortlve, af > disturbed antifeiiodistortive, d = dynamic, d = partially or planar dynamic].

Table 3. Stiuctuial and spectroscopic data of nitiocomplexes a m T (N02)6 (abbreviations for the type of Jahn-Teller order as in Table 2)...

Flgi 17. Cooperative Jahn-Teller ordering in complexes A2PbCu(N02)g (a) Antiferrodistortive order of elongated CuNg octahedra (small o-rhombic component) in 7-modifications [(001) planes, z = 0 z = 1/2 rotation of (z = 0) plane around [001 ] by 90° " )j (b) Incommensurate p-phase of K complex [from )] (c) Antiferrodistortive order in 7-phase and spatial disorder in p nodification of K complex ). 

Fig. 18. Antiferrodistortive Jahn-Teller ordering with disorder in one sublattice [from...

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