Ceramics in the system (Bi0.5K0.5)TiO3-BiFeO3 have good electromechanical properties and temperature stability. However, the high conductivity inherent in BiFeO3-based ceramics complicates measurement of the ferroelectric properties. In the present work, doping with niobium (Nb) is carried out to reduce the conductivity of (Bi0.5K0.5)TiO3-BiFeO3. Powders of composition 0.4(K0.5Bi0.5)Ti1−xNbxO3-0.6BiFe1−xNbxO3 (x = 0, 0.01 and 0.03) are prepared by the mixed oxide method and sintered at 1050 °C for 1 h. The effect of Nb doping on the structure is examined by X-ray diffraction. The microstructure is examined by scanning electron microscopy. The variation in relative permittivity with temperature is measured using an impedance analyzer. Ferroelectric properties are measured at room temperature using a Sawyer Tower circuit. Piezoelectric properties are measured using a d33 meter and a contact type displacement sensor. All the samples have high density, a rhombohedral unit cell and equiaxed, micron-sized grains. All the samples show relaxor-like behavior. Nb doping causes a reduction in conductivity by one to two orders of magnitude at 200 °C. The samples have narrow P-E loops reminiscent of a linear dielectric. The samples all possess bipolar butterfly S-E loops characteristic of a classic ferroelectric material. Nb doping causes a decrease in d33 and Smax/Emax.
Motivated by the recent work on β -alumina polycrystalline ceramics, we revisit the frequency dispersion behavior of AgI. Series of admittance and capacitance Bode plots at different temperatures revealed the presence of well-defined parallel capacitance effects and powerlaw frequency dependencies. Non-trivial bulk dispersion is thus successfully described by the bulk conductance with activation energy of 0.262 eV in parallel connection to several capacitive effects: (i) a mobile-charge contribution, universally observed in many solid electrolytes, approximated by a Cole-Davidson model with C ∼ = 28, γ C ∼ =0.388, and (τ C ) −1 thermally activated by 0.237 eV, (ii) a dipolar and vibratory contribution represented by another Cole-Davidson model of the dielectric strength of D ∼ = 9.0 with γ D ∼ =0.110, τ D ∼ =0.003 s, corresponding to Nearly-Constant-Loss behavior, and (iii) high frequency limit capacitance corresponding to the dielectric constant S ∼ =6.4. Electrode effects are described by an ideal Warburg response and the coefficient activated by 0.165 eV, which is connected in parallel to the bulk capacitive elements (i) to (iii). The modeling allows a simulation of ac behavior of AgI as a function of temperature as well as frequencies, addressing all of the universally observed dispersive responses.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.