Dependence of temperature variation of the Jahn-Teller
potential well splitting and phase transition temperature
in CuxZn1-xTiF6.6H2O crystals on Cu2+ ion
concentration, x
The energy Eo by which one of the three Jahn-Teller potential wells becomes lower than the other two
in Cu2+:ZnTiF6.6H2O single crystal at phase transition temperature, Tcl are determined at temperatures
below Tcl for different Cu2+ concentrations from the electron paramagnetic resonance (EPR) spectra.
As the sample is cooled, it is found that for high Cu2+ concentration, Eo increases below Tcl at a rate
much slower than that for low concentration and over a much broader temperature range. With the
increase of Cu2+ concentration, Tcl is found to decrease significantly. These findings appear to have a
bearing on the monoclinic distortion that proceeds in this system below Tcl. Qualitative explanation of
the decrease of Tcl with Cu2+ impurity concentration is presented. Eo is negligibly small for Cu2+
concentrations above certain limits means that the barrier height is also vanishing for such Cu2+
concentrations that is, phase transition of host lattice ceases. This is likely the reason for nonexistence
of phase transition in some compounds like CuTiF6.6H2O and ZnSiF6.6H2O belonging to the
same class with ZnTiF6.6H2O
