Separation and Purification Technology 73 (2010) 13–19 Contents lists available at ScienceDirect Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur Molecular dynamics simulation of the complex dopant effect on the super-ionic conduction and microstructure of zirconia-based solid electrolytes Kuo-Lun Tung ∗ , Kai-Shiun Chang, Chi-Chung Hsiung, Yen-Cheng Chiang, Yu-Ling Li R&D Center of Membrane Technology and Department of Chemical Engineering, Chung Yuan Christian University, Chung-Li, Taoyuan 320, Taiwan article info Keywords: SOFC Solid electrolyte Ionic conductivity Molecular dynamics MSD abstract The complex dopant effect on the super-ionic conduction and structural stability of zirconia-based solid electrolyte for solid oxide fuel cell (SOFC) applications was investigated using the molecular dynamics (MD) technique. Various components of Sc 2 O 3(x) –Y 2 O 3(1-x) were added to the cubic zirconia cell to build a scandia–yttria-stabilized zirconia (Sc–Y–SZ) model. The oxygen ion diffusion mechanism and ionic conductivity obtained by MD simulation were examined to gain insight into how the performance was improved by adding different Sc 2 O 3 concentrations. The radial distribution function (RDF) of the O–O pair was determined to analyze the oxygen ion mobility using microstructure analysis. The mean-square displacement (MSD) of the cations and RDF of the Zr–Zr pair were investigated to determine how the structural stability was affected by the concentration of doped Sc 2 O 3 . The simulated results were in agreement with the experimental data reported in the literature, suggesting that MD simulation is a feasible technique for use in the material design and development of SOFC applications. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Zirconia-based solid electrolyte doped with 8–10 mol% dopant is regarded as an effective ionic transport medium for high perfor- mance solid oxide fuel cells (SOFCs) applications [1]. However, the reduced ionic conductivity at the decreased operation temperature and various limitations in the high temperature region constrain the development of the SOFCs technology [2,3]. Therefore, it is desirable to improve the performance of the solid electrolytes in the intermediate-temperature range for commercial applications. To optimize the trade-off between performance and durability, many studies attempted to dope with a multi-component additive to improve the ionic conductivity at intermediate temperatures [2–6]. For instance, the effect of yttria doped in the Sc 2 O 3 –ZrO 2 system on cubic fluorite structure stability and the effect of scan- dia doped in the Y 2 O 3 –ZrO 2 system on ionic conductivity have been discussed [7]. In the Sc 2 O 3 -rich Sc–Y–SZ system, the ionic conductivity showed obvious deterioration at 1000 ◦ C due to the tetrahedron phase transformed from the cubic phase that was unfa- vorable for ion diffusion [8,9]. Moreover, the addition of BiO 2 in the ScSZ system may also help inhibit the phase transformation from cubic to rhombohedral by reducing the sintering temperature to maintain the structural stability [10]. The zirconia-based solid elec- trolyte with excellent ionic conductivity reached 0.16–0.18 S/cm at ∗ Corresponding author. Tel.: +886 3 2654129; fax: +886 3 2654199. E-mail address: kuolun@cycu.edu.tw (K.-L. Tung). 1273 K and was also successfully formed by doped complex dopant [3,4]. Hence, the doping of the electrolytes with complex additives is a superior way to develop super-conducted solid electrolytes at intermediate temperatures. However, the mechanism underlying the enhancement of ionic conductivity in the solid electrolyte upon doping the complex dopant was not fully understood. Insight at the molecular level to reveal the microstructure of complex dopant doped solid elec- trolyte and its performance of ionic conduction would be helpful for further in-depth study. In the past decade, it was discovered that molecular dynamics (MD) simulation is a feasible tool for micro- scale analyses [11–16]. Sawaguchi and Ogawa [12] found that the thermal motion of oxygen ions was mainly attributed to the “jump motion” at high working temperatures. The increased activation energy resulting from dopant addition was considered to be the major barrier for ionic conduction. Kilo et al. [13] compared the dif- fusion coefficient of oxygen ions inside the YSZ structure obtained from simulated and experimental work. The radial distribution function (RDF) of O–O, O–Zr and O–Y pairs was used to analyze the ion mobility in the YSZ structure. Devanathan et al. [14] analyzed the favored positions of oxygen vacancies inside the YSZ structure using the analysis of the coordination number of Zr +4 and Y +3 near the oxygen ions. The formation of a neutral Y ′ Zr –V O •• –Y ′ Zr cluster might be an important reason for the conductivity degradation of YSZ. Chen et al. [15] analyzed the interaction between neighboring oxygen ions using a density functional method to investigate the stability of a single and mixed doped cubic-ZrO 2 system. Ogawa et al. [16] discussed the high temperature deformation of ceram- 1383-5866/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.seppur.2009.07.026