<p>This study investigates the structural and electrical evolution of cerium dioxide (CeO₂) nanoparticles synthesized via an <i>Aloe vera</i>-mediated green route. The impact of post-synthesis thermal processing was evaluated by comparing samples sintered in ambient air (CAM) versus vacuum (CAV). While x-ray diffraction and Rietveld refinement confirmed a single-phase cubic fluorite structure for all samples, vacuum sintering significantly modified the electronic landscape. The CAV sample exhibited superior AC conductivity (−1.809 S cm⁻¹) compared to the CAM sample (−2.004 S cm⁻¹) at 400°C. X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations attribute this enhancement to reduced oxygen partial pressure, which promotes the formation of oxygen vacancies (<InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(V_{o}^{ \bullet \bullet }\)</EquationSource> <EquationSource Format="MATHML"><math> <msubsup> <mi>V</mi> <mrow> <mi>o</mi> </mrow> <mrow> <mo>∙</mo> <mo>∙</mo> </mrow> </msubsup> </math></EquationSource> </InlineEquation>) and Ce³⁺ polarons. Charge transport analysis indicates a transition from small polaron tunneling (SPT) to correlated barrier hopping (CBH) above 150°C. The electric modulus formalism also showed that the relaxation process is thermally activated and follows the time–temperature superposition principle (TTSP). These findings demonstrate that vacuum sintering is a critical lever for optimizing charge-carrier density in eco-friendly CeO₂, making it a viable candidate for IT-SOFCs and sensor applications.</p>