Dielectric and piezoelectric properties of modified lead-free NaNbO3–KNbO3/PVDF composite ceramics

This work presents the results of study of the electrophysical properties of composite polymer ceramics (1[Formula: see text][KNN-LTSN]–[Formula: see text]PVDF at [Formula: see text] = 25 vol.% and [Formula: see text]= 50 vol.% in the temperature range of [Formula: see text] = 20–160[Formula: see text]C and frequency range of [Formula: see text] = 2 × 101–2 × 106 Hz. The concentration dependence of piezomodules of the studied materials has been analyzed as a function of temperature. X-ray measurements have also been carried out. A model of description of revealed dielectric parameters dispersion in the material is presented. The nonclassical modified Havriliak–Negami model written for complex electrical conductivity has been used to describe the temperature–frequency properties. It is shown that the dielectric spectra of the studied composites include three relaxation processes in the temperature ranges of 40–80[Formula: see text]C, 80–120[Formula: see text]C and 120–150 [Formula: see text]C, which were confirmed by the dynamics of changes in the dependences of [Formula: see text], tg[Formula: see text], [Formula: see text], [Formula: see text]([Formula: see text]) and [Formula: see text]([Formula: see text]. All three processes are almost exactly described by this model and well correlated with the studies by other researchers of the composites based on PVDF. The results of this work show that the use of such experimental model is suitable for describing the complex dielectric spectra of any nonlinear dielectrics including composite materials.

Studying of dielectric spectra of YCu0.15Mn0.85O3 solid solution with the use of complex conductivity

This work presents the results of studying the electrophysical properties of the YCu[Formula: see text]Mn[Formula: see text]O3 solid solution in the range of temperatures of [Formula: see text] = 26–400[Formula: see text]C and frequency range of [Formula: see text] = 102–105 Hz. A model description of the revealed dispersion of dielectric parameters in the material is made. The nonclassical modified Havriliak–Negami model written for complex electrical conductivity was used as an approximation model. It is shown that the application of this model almost exactly describes the frequency behavior of the dielectric constant [Formula: see text]/[Formula: see text], the dielectric loss tangent tg[Formula: see text] as well as the real and imaginary parts of complex conductivity [Formula: see text] and [Formula: see text]. The results of this work are an important step in identifying the opportunities and understanding the applications of this model.

Complex dielectric permittivity, electric modulus and electrical conductivity analysis of Au/Si3N4/p-GaAs (MOS) capacitor

RF magnetron sputtering was used to grow silicon nitride (Si3N4) thin film on GaAs substrate to form metal–oxide–semiconductor (MOS) capacitor. Complex dielectric permittivity (ε*), complex electric modulus (M*) and complex electrical conductivity (σ*) of the prepared Au/Si3N4/p-GaAs (MOS) capacitor were studied in detail. These parameters were calculated using admittance measurements performed in the range of 150 K-350 K and 50 kHz-1 MHz. It is found that the dielectric constant (ε′) and dielectric loss (ε″) value decrease with increasing frequency. However, as the temperature increases, the ε′ and ε″ increased. Ac conductivity (σac) was increased with increasing both temperature and frequency. The activation energy (Ea) was determined by Arrhenius equation. Besides, the frequency dependence of σac was analyzed by Jonscher’s universal power law (σac = Aωs). Thus, the value of the frequency exponent (s) were determined.

Complex Electrical Conductivity of Biotite and Muscovite Micas at Elevated Temperatures: A Comparative Study

The unique physicochemical, electrical, mechanical, and thermal properties of micas make them suitable for a wide range of industrial applications, and thus, the interest for these kind of hydrous aluminosilicate minerals is still persistent, not only from a practical but also from a scientific point of view. In the present work, complex impedance spectroscopy measurements were carried out in muscovite and biotite micas, perpendicular to their cleavage planes, over a broad range of frequencies (10−2 Hz to 106 Hz) and temperatures (473–1173 K) that have not been measured so far. Different formalisms of data representation were used, namely, Cole-Cole plots of complex impedance, complex electrical conductivity and electric modulus to analyze the electrical behavior of micas and the electrical signatures of the dehydration/dehydroxylation processes. Our results suggest that ac-conductivity is affected by the structural hydroxyls and the different concentrations of transition metals (Fe, Ti and Mg) in biotite and muscovite micas. The estimated activation energies, i.e., 0.33–0.83 eV for biotite and 0.69–1.92 eV for muscovite, were attributed to proton and small polaron conduction, due to the bound water and different oxidation states of Fe.

Parameter of dielectric loss distribution in the new model for complex conductivity based on Havriliak–Negami formula

This paper is focused on the comparison of the results of various approximation models describing the frequency dependences of the dielectric constant [Formula: see text] and [Formula: see text], the tangent of the loss angle tg[Formula: see text] and the electrical conductivity [Formula: see text] and [Formula: see text] of nonlinear dielectrics. The classic ferroelectric material of the PZT system with [Formula: see text] was chosen as the object of study. Based on the analysis of temperature-frequency dependences of the “empirical” parameters [Formula: see text] and [Formula: see text], a regularity has been revealed that allows them to be calculated. A new relationship has been established through the parameter [Formula: see text], which allows to relate the temperature and frequency dependences of the complex electrical conductivity as [Formula: see text] and as [Formula: see text] in the Havriliak–Negami approximation models and in the new model for the description of the complex electrical conductivity [Formula: see text]. It is shown that [Formula: see text] is a parameter of the temperature-frequency distribution of dielectric losses. Using the obtained expressions, a new theoretical description of experimental spectra having a relaxation character was proposed. It has been proven that the use of the new model makes it possible to accurately describe the set of studied spectra, including the high and low frequencies, in the frequency range from [Formula: see text] to 108[Formula: see text]Hz.