Publications Details

Site Disorder as a Predictor for Compositionally Complex 5RE₂Zr₂O₇ Ceramic Phase Stability

Lowry, Daniel R.; Boro, Joseph R.; Foulk, James W.; Valdez, Nichole R.; Bishop, Sean R.

Here, phase formation and stability of five component compositionally complex rare earth zirconates (5RE₂Zr₂O₇) were investigated by X-ray diffraction and electron microprobe analysis. Zirconates with different rare earth compositions (LaNdSmEuDy, LaNdSmEuYb, LaNdEuErYb, LaNdDyErYb, SmEuDyYHo, LaYHoErYb, and DyYHoErYb) were synthesized at 1700°C and 2000°C by the solid-state method to investigate the effect of A-site site disorder (δ_A) on phase stability. Increased site disorder results from mixed cation occupancy with localized crystallographic strain and bond disorder. Compositions LaNdSmEuDy (δ_A = 4.6) and LaNdSmEuYb (δ_A = 6.0) produced a single pyrochlore phase and compositions SmDyYHoErYb (δ_A = 2.8), LaYHoErYb (δ_A = 6.2), and DyYHoErYb (δ_A = 1.7) produced a single fluorite phase. High δ_A compositions LaNdEuErYb (δ_A = 6.9) and LaNdDyErYb (δ_A = 7.2) produced a pyrochlore and fluorite phase mixture at 1700°C. Single phase was obtained for the latter composition at 2000°C. Of the single phase compositions calcined at 1700°C, LaNdSmEuYb and LaYHoErYb (both with largest δ_A) showed decomposition to mixed fluorite and pyrochlore phases during lower temperature anneals, indicating entropic stabilization. Comparison with prior work shows a temperature dependence of the critical δ_A for phase stability, and compositions near it are expected to be entropy stabilized.