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https://doi.org/10.1007/s11664-020-08449-4  2020 The Minerals, Metals & Materials Society

Impedance Spectroscopic Studies of B2O3-Substituted CeO2-Gd2O3 Systems N.S. CHITRA PRIYA,1,2,3 K. SANDHYA,1 and DEEPTHI N. RAJENDRAN1 1.—Department of Physics, Government College for Women, University of Kerala, Thiruvananthapuram, Kerala, India. 2.—Sree Chitra Thirunal Engineering College, Pappanamcode, Thiruvananthapuram, Kerala, India. 3.—e-mail: [email protected]

In this paper, the change in the conduction mechanism due to B2O3 addition in a ceria-based nanoceramic system is understood by studying the nature of conductivity and the variation of electric modulus function with frequency at different temperatures. The studies revealed that oxide ion conduction in the prepared system is prominent only after 500C. The activation energy for electrical conduction and oxide ion hopping in the system is found to be 0.26 eV and 0.85 eV, respectively. The discrepancy in the values of the activation energies itself is evidence of a different mechanism other than oxide ion hopping occurring in the present sample. The electric modulus function shows two relaxation peaks at lower temperatures corresponding to short-range and long-range relaxation for the charge carriers. Relaxation energies for the processes are found to be 0.27 eV and 0.95 eV. This is evidence of the occurrence of Maxwell–Wagner relaxation phenomena in the ceramic system. Explicitly, thermally activated oxide ion migration, along with the relaxation of electrons at the site of the bound pair (B–Vo)Æ is observed in the prepared nanocrystalline system. Key words: Solid oxide fuel cell, ceria, ionic conduction, hopping, activation energy, Maxwell–Wagner dielectric relaxation

INTRODUCTION Research on solid electrolytes has recently drawn much attention due to its application in solid oxide fuel cells (SOFCs), which convert the chemical energy of fuels directly into electrical energy with high efficiency. SOFC systems operate at high temperatures (800–1000C) with yttria-stabilized zirconia (YSZ) as the electrolyte material. The higher operating temperature offers advantages such as increased conductivity, faster electrode reactions without any expensive catalysts, fuel flexibility due to internal reforming and cogeneration possibility due to the high temperature of the expelled heat from the cell. But such high-temperature operation also has disadvantages like

(Received March 26, 2020; accepted August 25, 2020)

mechanical and chemical compatibilities, stability issues of the materials used, long start-up times and high cost of the materials and processing methods. Therefore, research on electrolyte materials suitable for lower operating temperatures (300C to 800C) is in high demand.1,2 Ceria-based ceramic systems are used as promising electrolytes in the intermediate-temperature region because of their higher ionic conductivity than YSZ. The nature of ceria electrolytes with respect to different dopants and dopant concentrations has been extensively investi