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

TL;DR

This study investigates how Yttrium doping affects the electrical conductivity, phase transitions, and polymorphism of LaCoO3 perovskite, revealing enhanced metallic properties and correlations with symmetry.

Contribution

It provides experimental insights into Yttrium's impact on LaCoO3's conductivity, phase behavior, and structural polymorphism, aligning with polaron hopping conduction models.

Findings

Yttrium doping increases metallicity in LaCoO3

Electrical conductivity follows polaron hopping model

Phase transitions and polymorphism are confirmed

Abstract

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 $LaCoO_3$, specifically its temperature dependence when doped with Yttrium (Y). The crystal structure of Lanthanum Yttrium Cobalt oxide $(La_{1-x}Y_x Co O_3)$ adopts a perovskite form, characterized by the general stoichiometry $ABX_3$, 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, $LaCoO_3$ exhibits polaron-type hopping conduction. Our aim was to understand the electrical conductivity at $300$ K and how it varies with temperature when $La^{3+}$ is replaced by $Y^{3+}$. 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 $Y^{3+}$ enhances the metallic properties of $La_{1-x} Y_x Co O_3$, and we found a significant correlation between conductivity and symmetry. Furthermore, the study highlights the material's phase transitions and polymorphic behavior.