Site Disorder as a Predictor for Compositionally Complex 5RE(2)Zr(2)O(7) Ceramic Phase Stability

Phase formation and stability of five component compositionally complex rare earth zirconates (5RE(2)Zr(2)O(7)) 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 & DEG;C and 2000 & DEG;C by the solid-state method to investigate the effect of A-site site disorder (& delta;(A)) on phase stability. Increased site disorder results from mixed cation occupancy with localized crystallographic strain and bond disorder. Compositions LaNdSmEuDy (& delta;(A) = 4.6) and LaNdSmEuYb (& delta;(A) = 6.0) produced a single pyrochlore phase and compositions SmDyYHoErYb (& delta;(A) = 2.8), LaYHoErYb (& delta;(A) = 6.2), and DyYHoErYb (& delta;(A) = 1.7) produced a single fluorite phase. High & delta;(A) compositions LaNdEuErYb (& delta;(A) = 6.9) and LaNdDyErYb (& delta;(A) = 7.2) produced a pyrochlore and fluorite phase mixture at 1700 & DEG;C. Single phase was obtained for the latter composition at 2000 & DEG;C. Of the single phase compositions calcined at 1700 & DEG;C, LaNdSmEuYb and LaYHoErYb (both with largest & delta;(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 & delta;(A) for phase stability, and compositions near it are expected to be entropy stabilized.