Colossal permittivity in titanium dioxide ceramics modified by tantalum and trivalent elements

Grain size effects on the dielectric properties of CaCu3Ti4O12 ceramics for supercapacitor applications

We have presented the dielectric/impedance spectroscopy of La1−xPbxFeO3 (x=0.15 and 0.25) polycrystalline samples in a wide temperature and frequency range. They exhibited colossal dielectric permittivity and multiple relaxations. Temperature and field dependent magnetization study showed enhancement of magnetization upon Pb doping which has been ascribed to the defect driven magnetization phenomenon. Overall we have emphasized the formation of various kinds of defects and their influence on dielectric and magnetic properties in the system.

Role of defects and oxygen vacancies on dielectric and magnetic properties of Pb2+ ion doped LaFeO3 polycrystalline ceramics

LuFe2O4 often is considered as a prototypical multiferroic with polar order arising from the electronic degrees of freedom only (“electronic ferroelectricity”). In the present work, we check the intrinsic nature of the dielectric response of this material by performing dielectric measurements of polycrystalline samples with different types of contact materials and with different grain sizes. In addition, frequency-dependent measurements of the electric-field dependent polarization are provided. The obtained results unequivocally prove that the reported colossal dielectric constants in LuFe2O4, which were interpreted in terms of electronic ferroelectricity, are of non-intrinsic surface-related origin. The intrinsic dielectric properties of this material show no indications of any ferroelectric order and, thus, LuFe2O4 is not multiferroic. Its intrinsic dielectric constant is close to 20 and its dielectric loss is dominated by charge transport via variable range hopping.

Absence of polar order in LuFe2O4

We report structural, magnetic, and dielectric properties of oxygen deficient hexagonal BaFeO3−δ. A large dielectric permittivity comparable to that of other semiconducting oxides is observed in BaFeO3−δ. Magnetization measurements indicate magnetic inhomogeneity and the system shows a paramagnetic to antiferromagnetic transition at ∼160 K. Remarkably, the temperature, at which paramagnetic to antiferromagnetic transition occurs, around this temperature, a huge drop in the dissipation factor takes place and resistivity shoots up; this indicates the possible correlation among magnetic and dielectric properties. First principle simulations reveal that some of these behaviors may be explained in terms of many body electron correlation effect in the presence of oxygen vacancy present in BaFeO3−δ indicating its importance in both fundamental science as well as in applications.

Large dielectric permittivity and possible correlation between magnetic and dielectric properties in bulk BaFeO3−δ

We report the detailed study on the colossal dielectric constant and magnetocapacitance of LuFe2O4. The experimental results indicate that the large dielectric constant of LuFe2O4 is originated from two sources, (1) Maxwell Wagner-type contributions of depletion layers at grain boundaries and the interfaces between sample and contacts, (2) AC response of the constant phase element in the bulk. A detailed equivalent circuit analysis indicates that the conductivity variation can be responsible for the observed “magnetocapacitance.”

C. H. A. Huan

Papers

Origin of the colossal dielectric permittivity and magnetocapacitance in LuFe2O4