Influences of sintering temperature on the electrical conductivity of GDC-50vol%MgO composite ceramics: the role of the
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ORIGINAL PAPER
Influences of sintering temperature on the electrical conductivity of GDC-50vol%MgO composite ceramics: the role of the GDC/MgO heterogeneous interface Qian Zheng 1 & Heng Zhang 1 & Bin Meng 1 & Wenke Liang 1 & Chen Li 1 & Xinyu Ping 1 & Zhidong Xia 1 Received: 28 August 2020 / Revised: 9 October 2020 / Accepted: 11 October 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Magnesium oxide can be added into Gd-doped CeO2 (GDC) as a suitable sintering additive, and the continuous GDC/MgO heterogeneous interface will contribute to the promotion of the oxygen ion transmission. GDC-50vol%MgO composite ceramics were sintered at different temperatures (1350~1500 °C). The phase composition, micromorphology, and electrical conductivity of GDC-50vol%MgO were analyzed by XRD, SEM, TEM, and electrochemical impedance, respectively. There are only GDC and MgO phases in the ceramics sintered at 1350 °C, 1400 °C, 1450 °C, and 1500 °C. As the sintering temperature rises from 1350 to 1500 °C, the average grain size of GDC and MgO increases from 239/274 to 680/651 nm, respectively. The GDC/MgO heterogeneous interface is clear, and many edge dislocations form there. The grain boundary and total conductivities decrease significantly with the rising sintering temperature, and the GDC/MgO heterogeneous interface possesses a higher electrical conductivity than the GDC/GDC homogeneous interface. Keywords Ceria-based composite ceramic . Gd-doped CeO2 . Magnesium oxide . Electrical conductivity . Heterogeneous interface
Introduction Doped CeO 2 –based ceramics are widely employed in intermediate-temperature solid electrolytes, oxygen sensors, and other fields because of their high ionic conductivity and excellent compatibility with electrode materials [1–3]. With the aid of doping with trivalent cations, a high concentration of oxygen vacancies can be introduced into the CeO2 lattice, thereby increasing the concentration of charge carriers [4–8]. It is reported that the Gd- or Sm-doped CeO2 (GDC or SDC) has exhibited the highest electrical conductivity in the doped CeO2–based ceramics [9]. However, the conduction of oxygen ions across the grain boundary is hindered due to the space charge layer effect and impurity blocking effect, resulting in the grain boundary electrical conductivity of
* Bin Meng [email protected] 1
Faculty of Materials Science & Engineering, Kunming University of Science & Technology, Kunming 650093, Yunnan Province, People’s Republic of China
CeO2-based ceramics being 2~3 orders of magnitude lower than that of the grain [10, 11]. Therefore, it has been a focus issue to improve the grain boundary conductivity of CeO2based ceramics. In order to weaken the effects of the space charge layer or impurity segregation on the grain boundary conduction behaviors of CeO2-based ceramics, it is an effective way to add some appropriate second phases into ceria to form composite ceramics. For example, some transition metal oxides (such as TiO2, ZnO, and Fe2O3) and alkaline earth metal oxi
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