<p>This research explored the impact of incorporating tin into commercial nickel paste as the internal electrode material for multilayer ceramic capacitors (MLCCs). By adjusting the tin content and varying reoxidation conditions, the study elucidates the influence of tin addition on the insulation resistance degradation of MLCCs. It was observed that tin addition led to the formation of a minor quantity of Ni₃Sn during the sintering process, which enhanced the continuity of the internal electrodes. This improvement increased the capacitance of the MLCC sample. However, tin diffused into the dielectric layer, replacing titanium sites as divalent ions and creating oxygen vacancies and Ti³⁺, thereby decreasing the resistance and breakdown voltage. Further investigations revealed that tin diffused into BaTiO₃ as divalent ions during reoxidation, substituting titanium sites and creating oxygen vacancies. The external oxygen interacted with free electrons generated by tin oxidation, forming adsorbed oxygen at the electrode interface during reoxidation. This reaction created a Schottky barrier, which inhibited leakage current and mitigated insulation resistance degradation. Additionally, forming a dense tin oxide layer during oxidation curtailed further oxidation of internal tin, maintaining the Schottky barrier height despite increased oxygen flow during reoxidation.</p>