Spray Solution Combustion Synthesis of In-Doped ZnO: The Fuel Effect on Microstructure and Thermoelectric Properties

ZnO is an earth abundant, safe, environmentally friendly, and relatively inexpensive resource for the application in the manufacturing of thermoelectric materials. In this work hollow spherical particles of Zn_0.995In_0.005O produced by the spray solution combustion synthesis (SSCS) with the stochiometric (φ₁) and excessive (φ₃) amount of glycine fuel were sintered at 900°C by the spark plasma sintering technique and thermoelectric properties of sintered Sφ₁ and Sφ₃ materials was measured. The best thermoelectric figure of merit zT ∼ 0.08 at 1050 K obtained for the materials produced at stoichiometric amount of fuel (φ₁). It was shown that lower amount of fuel (φ₁) used during the synthesis favors formation of porous and less textured structure which exhibits better thermoelectrical properties. The Lotgering factor (LF) calculated from the intensities of XRD (002) peaks was 0.65 for Sφ₃ sample, whereas for Sφ₁ sample LF (002) = 0.08. The average pore size of sintered Sφ₁ and Sφ₃ materials was around 200 nm. The total porosity was about 5–8% for Sφ₁ and 2–3% for Sφ₃ material.