Effects of partial Cu-doping on the structural, electrical, and dielectric properties of Ca2Fe2 − xCuxO5 (x = 0 and 0.05) brownmillerite oxides.

New compounds of the brownmillerite class Ca₂Fe_{2 − x}Cu_xO₅ (x = 0 and 0.05) have been prepared by a sol–gel process. Two new compounds have a main phase consisting of a "Pcmn space group" orthorhombic structure. According to microstructural analyses, the grains have a random geometrical morphology. The prepared samples presented a non-Debye relaxation phenomenon based on measurements of the electric modulus and impedance. The activation energy related to ac conductivity is close to the activation energy deduced from the electric modulus. This is an affirmation that the conduction and relaxation phenomena are managed by the same type of charge. Three types of conducting mechanisms can describe the process of conduction in our samples. An impressive influence of grain and grain boundaries on the dielectric properties was detected by the frequency and temperature dependence of dielectric permittivity and impedance measurements. The modelling of the Nyquist data was performed using the real and imaginary parts of the impedance, which were well adapted to equivalent electric circuits. [ABSTRACT FROM AUTHOR]