Molecular dynamics calculation of thermal expansion coefficient of a series of rare-earth zirconates

To develop more reliable and stable thermal barrier coatings, low thermal conductivity materials with higher thermal expansion coefficients (TECs), like rare-earth zirconates (A₂Zr₂O₇, A = La, Nd, Sm, Eu, Gd, Er, Yb and Lu), have been the focus of a great deal of attention in recent years. But the mechanisms underlying the values of TECs are still poorly understood. In this paper, the TECs of a series of rare-earth zirconates are calculated using molecular dynamics. Two typical crystal structures, pyrochlore and fluorite, are considered. By investigating the potential functions and the equilibrium-location deviations between the atoms, it is found that the Zr-O bond is the most important factor that determines the overall TECs, and the A-O bond plays a secondary role. However, O-O has little effect on the TECs. In addition, the fluorite structure has a relatively higher TEC due to a weaker Zr-O bond. Calculated values are consistent with the experimental observations. Using the method presented in this study, two doped zirconates (Gd_0.4Sm_0.5Yb_0.1)₂Zr₂O₇ and Sm₂(Ce_0.3Zr_0.7)₂O₇ are designed and compared. As expected, both of them have higher TECs than undoped Sm₂Zr₂O₇, and doping at the A-site is more efficient than doping at the Zr-site.