Cooperative Jahn‐Teller Orbital Ordering in KCuF 3 and K 2 CuF 4 Crystals

Two mechanisms of Cu 2+ orbital ordering in KCuF 3 and K 2 CuF 4 are considered: the Jahn‐Teller and the exchange mechanisms with account of the crystal elastic energy. The Jahn‐Teller coupling constants and exchange parameters necessary for the evaluation of angles characterizing the orbital and crystal structures of crystals are estimated. It is shown that the exchange mechanism alone cannot explain the experimentally observed values of orbital structure angles. Within the frames of the Jahn‐Teller mechanism both, orbital and magnetic structures of KCuF 3 and K 2 CuF 4 are explained and the connection between the orbital structure angles of these crystals is established and also a qualitative explanation of the orbital structure angle values experimentally observed in MnF 3 and KCrF 3 is given. [Russian Text Ignored]