The conductivity and elastic modulus Of (CeO2)(1 - x)(YO1.5)(x) for x values of 0.10, 0.15, 0.20, 0.30, and 0.40 were investigated by experiments and molecular dynamics simulations. The calculated conductivity exhibited a maximum value at approximately 15 mol% Y2O3: this trend agreed with that of the experimental results. In order to clarify the reason for the occurrence of the maximum conductivity. the paths for the transfer of oxygen vacancies were counted. The numerical result revealed that as the content Of Y2O3 dopant increases, the number of paths for the transfer of oxygen vacancies decreases, whereas the number of oxygen vacancies for conductivity increases. Thus, the trade-off between the increase in the number of vacancy sites and the decrease in the vacancy transfer was considered to be the reason for the maximum conductivity occurring at the Y2O3 dopant content of approximately 15 mol%. The calculated elastic modulus also exhibited a minimum value at approximately 20 mol% Y2O3, which also agreed with the experimental results. It was shown that the Y-O-Y bonding energy increased with the increasing content of Y2O3 dopant. Thus, the trade-off between the increase in the number of vacancy sites and that in the Y-O-Y bonding energy was considered to be the reason for the minimum elastic modulus occurring at the Y2O3 dopant content of approximately 20 mol%. (C) 2009 Elsevier B.V. All rights reserved.