Dielectric relaxation processes in Cd2Nb2O7 compound

This article reports a study on the dielectric relaxation processes of Cd2Nb2O7 compound. Three dielectric relaxation modes I, II, and III were reexamined. By using the Cole-Cole equation fitting of the frequency dependence of dielectric constant and loss, we obtained more precise relaxation time data, compared to the data reported in the literature. The results indicate that the relaxation time for mode I follows the Arrhenius law with one slope rather than two slopes as reported in the literature in the frequency range of 10(2)-10(5) Hz. However, the parameters obtained from the Arrhenius law fit are not physically reasonable. More physically reasonable parameters can be obtained by fitting the relaxation time to the empirical Vogel [Z. Phys. 22, 645 (1921)]-Fulcher [J. Am. Ceram. Soc. 8, 339 (1925)] relation with essentially the same fitting quality. A comparison of Cd2Nb2O7 with well known triglycine sulphate (TGS) is made. The similarity between the dielectric response of Cd2Nb2O7 and TGS is emphasized. The physical mechanism of the relaxation modes is briefly discussed. With increasing dc bias, the three relaxation modes were suppressed and eventually eliminated. This indicates that the dielectric responses of Cd2Nb2O7 at zero dc bias are the sum effect of several dielectric modes with relaxation polarization superimposed on the ferroelectric-paraelectric phase transition. (C) 2000 American Institute of Physics.