Aluminum-Doped Zinc Oxide Ceramics with Improved Thermoelectric Properties via a Simple Pechini Based Sol Gel Method

Abstract In this study, zinc oxide (ZnO) ceramics were synthesized by a modified Pechini sol-gel method, replacing conventional zinc nitrate with zinc acetate to provide a distinct chemical environment and avoid toxic emissions during heat treatment. To the best of our knowledge, this work represents the first time this acetate-based Pechini route is investigated from a thermoelectric perspective. This approach offers a scalable, inexpensive, and non-toxic route with precise compositional control. To enhance thermoelectric performance, the powders were doped with 2% aluminum and subjected to optimized mechanical milling before sintering. Structural and microstructural characterizations confirmed the formation of a pure ZnO wurtzite phase with well-distributed dopants and refined grain morphology. Thermoelectric measurements revealed that aluminum doping significantly increases electrical conductivity. The best results were obtained for milled ZnO-2%Al powders sintered at 1400 °C for 6 h, yielding a Seebeck coefficient of -150 µV. K − 1 and a power factor of 138 µW.m − 1 . K − 2 at 700 °C. The corresponding ZT value reaches 0.012, demonstrating that this protocol provides a highly effective and industrially scalable alternative to more complex, capital-intensive methods such as Spark Plasma Sintering (SPS). An original analysis based on an effective medium approach (EMA) is presented to decouple the competing effects of porosity and doping. We demonstrate that while the system is highly sensitive to connectivity losses induced by porosity, the electronic gain from aluminum doping significantly overshadows these structural penalties. These results confirm the potential of the acetate-based Pechini method, combined with controlled doping and milling, as a simple, cost-effective, and processing-flexible route, paving the way for both bulk ceramics and easy-to-deposit thick or thin film geometries for the industrial-scale development of oxide-based thermoelectric materials.