Study of diffuse phase transition and relaxor ferroelectric behavior of Ba0.97Bi0.02Ti0.9Zr0.05Nb0.04O3 ceramic

In the present work, structural and dielectrics properties of polycrystalline sample Ba_0.97Bi_0.02Ti_0.9Zr_0.05Nb_0.04O₃ (BBTZN) prepared by a molten-salt method were investigated. X-ray diffraction analyses revealed the formation of a single-phase pseudocubic structure with a Pm3̄m space group. Unlike the trend observed in classic ferroelectrics, the temperature dependence of the dielectric constants showed the presence of three sequences of structural phase transitions. In fact, the local disorder provides a frequency dependent relaxor like behaviours attributed to the dynamic of polar nanoregions (PNRs). The diffuse phase transition (DPT) analyzed using the modified Curie–Weiss law and Lorenz formula confirms the presence of short-range association between the nanopolar domains. The obtained values of the degree of diffuseness are found to be in the range of 1.58–1.78 due to the existence of different states of polarization and, hence, different relaxation times in different regions. The frequency dependence of temperature at dielectric maxima, which is governed by the production of PNRs at a high temperature, satisfies the Vogel–Fulcher (V–F) law. The temperature dependence of the electric modulus for various frequencies indicating a thermally activated relaxation ascribed to the Maxwell–Wagner (M–W) space charge relaxation phenomenon.

In the present work, structural property of polycrystalline sample Ba_0.97Bi_0.02Ti_0.9Zr_0.05Nb_0.04O₃ (BBTZN) prepared by a molten-salt method were investigated.

Frequency and temperature-dependence of dielectric permittivity and electric modulus studies of the solid solution Ca0.85Er0.1Ti1−xCo4x/3O3 (0 ≤ x ≤ 0.1)

The dielectric properties of Ca_0.85Er_0.1Ti_1−xCo_4x/3O₃ (CETCo_x) (x = 0.00, 0.05 and 0.10), prepared by a sol–gel method, were systematically characterized. The temperature and frequency dependence of the dielectric properties showed a major effect of the grain and grain boundary. The dielectric constant and dielectric loss of CETCo_x decreased sharply with increasing frequency. This is referred to as the Maxwell–Wagner type of polarization in accordance with Koop's theory. As a function of temperature, the dielectric loss and the real part of permittivity decreased with increasing frequency as well as Co rate. Indeed, a classical ferroelectric behavior was observed for x = 0.00. The non-ferroelectric state of the grain boundary and its correlation with structure, however, proved the existence of a relaxor behavior for x = 0.05 and 0.10. The complex electric modulus analysis M*(ω) confirmed that the relaxation process is thermally activated. The normalized imaginary part of the modulus indicated that the relaxation process is dominated by the short range movement of charge carriers.

Frequency dependence of real (ε′) part of permittivity of CETCo_x for x = 0.00, 0.05 and 0.10 for T = 600 K.