Effect of morphology on the thermoelectric properties of pure nanostructured zinc oxide

Abstract

This article investigates the effect of morphology on the thermoelectric properties of nanostructured zinc oxide. Three different samples of nanostructured zinc oxide, named ZnO, ZnO triethanol amine (TEA) and ZnO Calc., were synthesized. ZnO and ZnO TEA samples were synthesized by the chemical precipitation method, while ZnO Calc. sample was prepared by the direct calcination method. The FESEM analysis revealed that ZnO and ZnO Calc. samples have flakes and nanorod-like morphology, respectively, while ZnO TEA has a mixed hexagonal and irregularly shaped morphology. The Rietveld refinement of X-ray diffraction data confirmed that all the prepared samples have a hexagonal wurtzite phase of ZnO with space group P6₃mc. The energy-dispersive X-ray spectroscopy confirmed the presence of zinc and oxygen in all the synthesized samples. The electrical resistivity and Seebeck coefficient were recorded in the temperature range of 300–950 K. The negative values of the Seebeck coefficient revealed the n-type nature of all the samples. The increase in electrical resistivity with the increase in temperature confirmed that all three prepared ZnO samples show metallic behaviour. The highest Seebeck coefficient of –245 μV K^–1 was attained by ZnO nanorods at 950 K, while the lowest Seebeck coefficient of –212 μV K^–1 was obtained for ZnO TEA at 950 K. The highest thermoelectric power factor of 2.11 \(\times \, {10}^{-3}\) W m^–1 K^–2 was attained by the ZnO Calc. sample at 950 K. The results indicate that the synthesized ZnO Calc. sample with nanorod-like morphology has better thermoelectric performance as compared to flakes and platelets-like morphology.