In the EPR spectra of the Cs2Zn(ZrF6)(2).6H(2)O crystal doped with the Cu-63(2+) isotope the feature of plasticity, inherent to the Jahn-Teller (JT) effect, is observed directly enabling its deeper understanding. The Q- and X-band EPR shows the temperature- and pressure-induced transformations of the shape of the doped Cu(H2O)(6) complex resulting in the interchange of the elongation directions. These transformations are explained as being due to the action of the ferroelastic spontaneous strain. The room temperature direction of the JT complex deformation differs from that expected from the shape of the host complex leading the conclusion that is determined by the various competing interactions. (C) 2003 Elsevier B.V. All rights reserved.