4 research outputs found
Relaxation phenomenon in composite materials
Dielectric measurement characteristics such as the dissipation factor, relative permittivity and conductivity as a function of temperature and frequency have been achieved on composite materials based on different epoxy resins filled with alumina inclusions. The analysis of the results show the presence of porosity and inhomogeneity in these materials. The study of the dissipation factor, as a function of temperature at high frequencies, has shown an unexpected absorption phenomenon in materials designed to be utilized as electrical insulators. The identification of the entities responsible for this relaxation shows that the entities result from one of the components of the material. These results can also confirm the inhomogeneity of the material
Dielectric and structural properties of diffuse ferroelectric phase transition in Pb
We studied the structural and dielectric properties of new Tetragonal
Tungsten Bronze (TTB) ceramics
Pb1.85K1.15Li0.15Nb5O15 that was synthesized by
solid-state reaction. We pay a special attention to the diffuse phase
transition (DPT) that occurs close to 425 °C. Using dielectric
measurements in a frequency range of 10 Hz–1 MHz and in the temperature range
30–560 °C, we have shown that the real permittivity close to DPT is well
described by Santos-Eiras phenomenological model. Space-charge
polarization, relaxation phenomena and free charges conductivity have been
analyzed using dielectric spectroscopy impedance and modulus
characterization. Cole-Cole plots show a non-Debye (polydispersive) type
relaxation. In paraelectric phase the Arrhenius activation energy was
determined as EÏ„ = 0.72Â eV. We demonstrated that frequency
dependence of ac conductivity at different temperatures obeys the
Jonscher's universal law: σac = σdc + A(ω)n