Influence of zinc incorporation on the structure and conductivity of lanthanum ferrite

LaFe1−xZnxO3−δ (x=0, 0.1, 0.15 and 0.2) compounds were successfully synthesized using the polymerisable complex method. Their structural and electrical properties were investigated. The X-ray diffraction and infrared analyses revealed the formation of single perovskite phases for x=0, 0.1 and 0.15. The orthorhombic structure of the parent oxide was preserved for the substituted compounds. The electrical properties of lanthanum ferrites were investigated using complex impedance spectroscopy. For all the studied compositions, results reveal a semi-conducting behavior between 350 and 800 °C. Conductivity of the Zn2+ substituted compounds is significantly improved. At 800 °C, its value for the LaFe0.85Zn0.15O3−δ oxide is five times higher than that of LaFeO3. Furthermore, anomalies in the Arrhenius plots are observed around the Neel temperature TN. They are associated with the second order magnetic transition of lanthanum ferrite. TN decreases from 440 °C for LaFeO3 to 428 °C for LaFe0.85Zn0.15O3−δ. Such decrease is attributed to the increased distortion of the perovskite lattice. In the frequency range of 5 Hz to 13 MHz, the alternating current conductivity fits to a simple power law behavior σac(ω)=σdc+AωS. At fixed temperature, σac increases with Zn content.