Electrical and Photocatalytic Characterizations of Rare Earth Modified Layered Ferroelectric SrBi2Ta2O9 Ceramics

Abstract

Aurivillius compound SrBi2Ta2O9 (SBT) is a futuristic material with applications mainly in ferroelectric memory devices. This is due to their excellent fatigue resistance and other electrical properties. Besides, these materials can be synthesized by a relatively easy preparation process. Most importantly, all the constituents of parent material and/or by modifications, as a whole are environmentally safe. In the present thesis various physical properties such as structural, surface morphology, electrical and photocatalytic analysis of SBT and its substitutions (Ce4+, Dy3+ and Y3+) are studied. X-Ray diffraction patterns reveal a single phase orthorhombic (A21am) structure for SBT and its compositions. Secondary phases are obtained for higher concentration in all the compositions which proves the presence of solubility limit. Scanning electron microscopic figures are identified with highly densed and well defined anisotropic grains in all the compositions. Substitutions at A-site and Bi-layer with rare earth elements (Dy3+, Y3+ and Ce4+) effectively modifies the electrical properties as well as photocatalytic analysis. The temperature dependence dielectric study shows the nature of ferroelectric phase transition in these materials. Trivalent elemental substitutions at A-site induce cation vacancies to satisfy the charge neutrality, which significantly improve the ferroelectric property. Hysteresis measurement confirms the perfect ferroelectricity and fatigue property of the samples. The enhanced dielectric and ferroelectric properties are identified upto solubility in all the compositions. The electrical relaxation mechanism is studied by the impedance spectroscopy analysis. The Cole–Cole plots are analyzed with the suitable equivalent circuits and the parameters are extracted. The Kohlrausch–Williams–Watts function is used to explain the modulus analysis to suppress the space charge polarization and to confirm whether the grain and grain boundary effects are present. The ac and dc conductivity behavior of these materials are examined by Joncher’s power law, and Arrhenius law. All these results confirm the defect induced mechanism responsible for observed conductivities. The determined activation energies give an idea about the reduction of a vacancy clusters due to the neutralization of oppositely charge vacancies. Finally, the photocatalytic activities for water splitting are investigated under UV-light irradiation. It is observed that the photogenerated electrons and holes are separated spontaneously by ferroelectric domains to enhance the H2/O2 evolution. For better understanding of ferroelectric as a photocatalyst, the relation between electrical and photocatalytic properties are correlated.