Date of Award

5-1-2018

Degree Name

Master of Science

Department

Mechanical Engineering

First Advisor

Mondal, Kanchan

Abstract

Developing electrolyte operating at low temperature is crucial for the development of efficient solid oxide fuel cell and also energy device, operating over wide temperature domain. In this study, co-doped ceria, with compositional formula Ce1-x-yZrxYyO2-y/2, is prepared through co-precipitation method. When doped in ceria, yttria being aliovalent dopant induces oxygen vacancies for ionic conduction, while zirconia being isovalent dopant increases mobility of vacancies and also mechanical strength of the material. This study is intended to find the optimal doping level for conductivity, with good mechanical stability and rigidity. Compared to undoped ceria, all compositions showed better conductivity, however density and hardness have been decreased. Maximum conductivity, although, found for the singly doped ceria with aliovalent dopant in almost all levels, structural properties were found to be enhanced with the zirconia doping. Zirconia doping initially caused the reduction of conductivity, in all constant yttria doping levels. Study shows the minimum level of conductivity at around x=y, and then enhancement in the conductivity level was observed. Phenomenon is possibly explained by the vacancy clustering around the cations, defects association, local ordering of vacancies, formation of migration barriers reducing the conductivity at lower zirconia doping level and then the dilution effect of doping increasing the conductivity at higher doping level of zirconia. Among all the studied compositions, x=0 and y=5 proportion of mass fraction showed maximum conductivity, possibly due to the better lattice arrangement, or because of the best doping fraction of yttrium being 1/24th of total ion concentration, But, the composition needs furthermore study to conform the conductivity maxima occurrence. X=0 and x=2 with y=10 also showed high conductivity which is explained by the optimal doping fraction of yttrium being 1/12th of cerium ion concentration, where it is expected to form maximum vacancies with minimum defect association. Density have decreased with the yttrium ion concentration increase and then again increased. Hardness increased with the increasing zirconia addition and decreased with increasing yttria concentration. X-Ray diffraction test revels the pattern with the phase in the material unchanged but with the of additional peaks for the cerium zirconium oxide is observed with zirconia addition. Lattice parameters have changed with changing doping level. SEM of powder have showed the material without any segregation of the particles, while SEM of particles have showed the minute pores in the surface. EDS test shows the presence of the materials used with some impurities.

Available for download on Friday, March 08, 2019

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