Influence of Yttrium(Y) on properties of Lanthanum Cobalt Oxides

Many materials exhibit various types of phase transitions at different temperatures, with many also demonstrating polymorphism. Doping materials can significantly alter their conductivity. In light of this, we have investigated the electrical conductivity of LaCoO₃, specifically its temperature dependence when doped with Yttrium (Y). The crystal structure of Lanthanum Yttrium Cobalt oxide (La₁₋ₓYₓ Co O₃) adopts a perovskite form, characterized by the general stoichiometry ABX₃, where A and B are cations, and X is an anion. This material undergoes a magnetic phase transition between $50-100$ K, a structural phase transition between $100-300$ K, and an insulator-to-metal transition at $500$ K. At room temperature, LaCoO₃ exhibits polaron-type hopping conduction. Our aim was to understand the electrical conductivity at $300$ K and how it varies with temperature when La³⁺ is replaced by Y³⁺. The electrical properties of the perovskite crystal are consistent with small polaron hopping conduction, which theoretically follows Mott's variable range hopping model, where conductivity obeys an exponential law, and resistivity follows an inverse exponential pattern. In this work, we compare the experimental resistivity graph with the theoretical inverse of the conductivity graph, showing that our experimental results align with the polaron hopping conduction model within a certain range. Additionally, the experiment confirms polymorphism in various cases. We observed that increasing the concentration of Y³⁺ enhances the metallic properties of La₁₋ₓ Yₓ Co O₃, and we found a significant correlation between conductivity and symmetry. Furthermore, the study highlights the material's phase transitions and polymorphic behavior.