The influence of sintering processing on microstructural, optical and electrical properties of zinc oxide ceramics doped with Al3+, B3+, Mg2+

Abstract

Zinc oxide (ZnO) is a versatile functional material, widely employed in industry and technology as varistor ceramics, transparent conducting films, surface acoustic wave resonators etc. ZnO-based conductive ceramics, attractive for various applications, should have low electrical resistivity and good linearity. The n-type conductivity of wide band gap (3.37 eV) ZnO semiconductor could be enhanced by multiple doping with trivalent metals (B3+, Al3+, Ga3+, In3+), as shallow donors. The intrinsic defects, zinc vacancies and interstitial oxygen, exist in the grain boundaries of n-type ZnO ceramics as localized acceptor states. These states attract charge carriers, creating a depletion region around the grain boundaries and energy potential barrier, which hinder the motion of the electrons [1]. In this work, zinc oxide ceramics doped with Al3+, B3+ and Mg2+ was prepared using solid-state reaction technique from ZnO powder obtained in solvothermal synthesis and Al2O3, MgO and B2O3 (H3BO3) commercial powders. Al2O3 was used as a donor dopant to increase the carrier concentration, B2O3 was added to enhance densification and grain growth, and MgO – to decrease the thermal conductivity [2,3]. The pressed ZnO (0.25 % Al2O3, 0.5 % B2O3, 1 % MgO) pellets were sintered by conventional (CS) and spark plasma (SPS) method. The ceramic samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-Vis spectroscopy and current-voltage (I–U) measurements. The correlation between the sintering processing, microstructure and electrical properties of multiple doped ZnO-based ceramics was investigated. The electrical performances of ZnO (0.25 % Al2O3, 0.5 % B2O3, 1 % MgO) ceramics were strongly dependent on composition and microstructure (density, grain size, segregation of secondary phase in grain boundaries). The electrical resistivity of SPS sample was an order of magnitude lower than electrical resistivity of CS sample and it showed almost linear I-U characteristics in temperature range of (25–150) C. 1. T.K. Gupta, W.G. Carlson, J. Mater. Sci., 20 (1985) 3487 2. T. Tian, L. Cheng, J. Xing, L. Zheng, Z. Man, D. Hu, S. Bernik, J. Zeng, J. Yang, Y. Liu, G. Li, Mater. Design, 132 (2017) 479 3. B. Yuksel, T. O. Ozkan, Mater. Sci. – Poland, 33 (2015) 220