Sintering Behavior and Thermoelectric Properties of Al‐ and Mg‐Doped ZnO: Effect of Grain Boundary Segregation

ABSTRACT This study investigates the influence of isovalent Mg and aliovalent Al dopants on the sintering behavior and thermoelectric properties of ZnO ceramics. ZnO nanopowders synthesized via the coprecipitation method were consolidated using spark plasma sintering across varying dopant concentrations and sintering temperatures. Scanning electron microscopy–energy‐dispersive X‐ray spectroscopy analysis revealed that Al doping induces grainboundary segregation, promoting grain refinement and improved densification, whereas Mg doping results in a more homogeneous distribution of dopant ions within the ZnO matrix. Thermoelectric measurements indicate that increased density and grain growth at elevated sintering temperatures enhance electrical and thermal conductivity proportionally; however, a marked reduction in the Seebeck coefficient leads to diminished zT values under these conditions. Notably, ZnO doped with 1.5 wt.% Al and sintered at 700°C achieves a maximum zT of ∼0.0025 at 300 K. In contrast, 1.5 wt.% Mg‐doped ZnO sintered at 1000°C reaches a zT of ∼0.0013 at 300 K, outperforming Al‐doped samples processed at the same temperature. These results underscore the critical role of porosity and grain growth in governing the thermoelectric performance of doped ZnO ceramics. Overall, the findings offer valuable insights into the interplay between dopant chemistry and microstructural evolution, paving the way for environmentally stable and cost‐effective oxide‐based thermoelectric materials.