Effects of Sc doping on phase stability of Zr1 – xScxO2 and phase transition mechanism: First-principles calculations and Rietveld refinement

Abstract

Scandia doped zirconia (ScSZ) is a promising electrolyte candidate for Solid Oxide Fuel Cells (SOFCs). However, the cubic-tetragonal phase transition of ScSZ is a serious problem that blocks its extensive application. A systematic study of tetragonal and cubic phase stability of Zr1–xScxO2 as a function of x is carried out using density functional theory (DFT) calculations. The optimized atomic structures and total energies are obtained. The cubic phase becomes stable when x>0.18. The largest tetragonal and cubic phase's total energy difference appears at x=0.2188, which indicates that the cubic phase is most stable at this doping level. Furthermore, experiments have been carried out to verify the calculation reliability. The calculation results match well with our Rietveld refinement and Raman scattering observations. The relative phase transition mechanism has been analyzed systematically according to the calculated results and optimized atomic configuration. The phase structure transformation is shown to be closely correlated with cell volume difference, coordinated situation and oxygen displacement.