The phase tt':lnsition in cadmium calcium acetate hexahydrate (CCDAH) has been studied in detail with
electron paramagnetic resonance (J;PR) as a function of two different paramagnetic ion concentrations. namely.
Cu:• and Mn:• ions. The change in transition temperature (1:!2-143 Kl with Cuz• ion concentrations is
explained in terms of mean-field theory and a soft vibrational mode of the -Ca-Cd1 _ ,Cu,-Ca- chain along the
c axis of the crystal. While the same theory can also explain our observed transition temperature ( 118-128 K)
as a function of the Mn2• ion concentration in this crystal. it does not explain why the limiting value of the
transition temperature (i.e .• 145 K) of CaCd1 -.,CuzCCH3C00)4 ·6H~O as x tends to zero, is strikingly different
from the limiting value of ( -128..+ K) of CaCd1_.,Mn,(CH3C00)4·6H:O as x tends to zero. The same theory
also successfully c:xplains the absence of any phase transition in isomorphous CaCu(CH 3C00)~·6H 20. The
value of -dT~Id.t is significantly higher with Mn:• than with Cu!• in CCDAH. [50163-1829(97)01329-5
