Phase Transformation and Lattice Parameter Changes of Non-trivalent Rare Earth-Doped YSZ as a Function of Temperature

Abstract

To examine the effect of doping/co-doping on high-temperature phase compositions of YSZ, stand-alone YSZ and CeO₂ and Nb₂O₅ co-doped YSZ samples were prepared using mechanical alloy and high-temperature sintering. XRD analysis was performed on these samples from room temperature to 1100 °C. The results show that the structure for the co-doped samples tends to be thermally stable when the test temperature is higher than a critical value. Monoclinic phase was dominant in Nb₂O₅ co-doped YSZ at temperatures lower than 600 °C, while for the YSZ and CeO₂ co-doped YSZ, cubic/tetragonal phase was dominant in the whole test temperature range. The lattice parameters for all the samples increase with increasing test temperature generally. The lattice parameters for the two non-trivalent rare earth oxides co-doped YSZ show that the lattice parameter a for the cubic phase of the Ce⁴⁺ co-doped YSZ is consistently greater than that of 7YSZ which is related to the presence of larger radius of Ce⁴⁺ in the matrix. The lattice parameters a, b, c for the monoclinic phase of Ce⁴⁺ co-doped YSZ are much closer to each other than that of the Nb⁵⁺ co-doped YSZ, indicating the former has better tendency to form cubic/tetragonal phase, which is desired for vast engineering applications.