EPR studies of the effect of Zn2+ ion impurities in phase transition of CaCd(CH3COO)4•6H2O crystals -: art. no. 174414

The effect of Zn2+ ion impurities on the phase transition temperature of single crystals of calcium cadmium acetate hexahydrate (CCDAH) has been studied using the electron-paramagnetic-resonance technique. The lowering of the phase transition temperature as a function of increasing Zn2+ impurity ion concentration in the crystals has been observed to be quite different from that found in our earlier studies of Cu2+ and Mn2+ ion doped crystals. Though the observed lowering of phase transition temperature with atomic fraction x of the Zn2+ impurity ion can be explained fairly well in terms of mean-field theory and a soft mode arising out of the harmonic vibration of the Ca-Cd(1-x)Znx-Ca chain along the c axis of the crystal, contrary to expectation, values of constants (such as the ratio of the square of the soft-mode frequency before transition, the mean-field constant, and the phase transition temperature, etc. of the pure crystal) are quite different from that obtained by fitting the phase transition temperatures in the Cu2+ ion only impurity doped crystals. The temperature variation of the spin-Hamiltonian parameters of the Cu2+ ion probe in the Zn2+-doped crystal of CCDAH is somewhat different from that in the Cu2+ ion only doped crystal. Deviation from mean-field theory is then considered in the Zn2+ impurity driven modification of phase transition of the crystal and good agreement between the observed and computed values of phase transition temperature as a function of the Zn2+ atomic fraction has been obtained using the same values of the said constants as obtained for Cu2+ ion only impurity doped crystals.