EPR STUDIES OF PHASE TRANSITIONS IN CADMIUM CALCIUM ACETATE HEXAHYDRATE AS A FUNCTION OF DIFFERENT PARAMAGNETIC IMPURITY-ION CONCENTRATIONS

摘要

The phase transition in cadmium calcium acetate hexahydrate (CCDAH) has been studied in detail with electron paramagnetic resonance (EPR) as a function of two different paramagnetic ion concentrations, namely, Cu2+ and Mn2+ ions. The change in transition temperature (122-143 K) with Cu2+ ion concentrations is explained in terms of mean-field theory and a soft vibrational mode of the -Ca-Cd1-xCux-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-xCux(CH3COO)(4) . 6H(2)O as x tends to zero, is strikingly different from the limiting value of (similar to 128.4 K) of CaCd1-xMnx(CH3COO)(4) . 6H(2)O as x tends to zero. The same theory also successfully explains the absence of any phase transition in isomorphous CaCu(CH3COO)(4) . 6H(2)O. The value of -dT(c)/dx is significant higher with Mn2+ than with Cu2+ in CCDAH. [References: 36]