Electrochemical properties of Iron-Containing Bismuth Titanates with the Layered Perovskite Structure

Solid solutions of Bi4Ti3-x Fe (x) O12-0.5x with the perovskite structure in which a part of titanium atoms are replaced by iron atoms and the total amount of iron and titanium remains constant are studied. The structural transformations of compounds in the temperature interval of 25-850 degrees C are examined by the X-ray diffraction method. It is shown that depending on the iron content, the crystal structure with the number (m) of octahedral layers in perovskite blocks equal to 3 or 4 can be formed. Compounds Bi4Ti1.3Fe1.7O11.15 (m = 4) and Bi4Ti2.6Fe0.4O11.8 (m = 3) are studied in detail by the impedance spectroscopy method. The ionic component of conductivity manifests itself after the treatment at 600 degrees C for the former compound and at 450-500 degrees C for the latter. This is accompanied by minor deformations of the solid solution structure. A strong effect of the constant potential on the impedance spectra of samples is observed as well as the appearance of negative capacitance in the frequency range below 1 Hz. Based on the results of studies, the electronic-ionic conduction of Bi4Ti3-x Fe (x) O12-0.5x is inferred.