Chemical durability and release mechanisms of Sr0.5Zr2(PO4)3–high-entropy (Ln1/n)PO4 monazite dual-phase ceramics for high-level waste immobilization

In this work, Sr 0.5 Zr 2 (PO 4 ) 3 –high-entropy ( Ln 1/ n )PO 4 monazite dual-phase ceramics with n  = 5, 6, and 7 were prepared by microwave-assisted sintering for high-level waste immobilization, where Ln 1/5 = (La, Nd, Sm, Eu, Gd) 1/5 , Ln 1/6 = (La, Nd, Sm, Eu, Gd, Dy) 1/6 , and Ln 1/7 = (La, Nd, Sm, Eu, Gd, Dy, Ho) 1/7 . After 28 days of leaching at pH 4.0, 6.2, and 10.0, the LR Sr and LR Ln-average values for the n  = 5 samples were 10 −4 –10 −3 and ∼10 −6 g·m −2 ·d −1 , respectively. Both phases exhibited optimal chemical durability at pH 6.2, and Sr and Ln release mechanisms were pH-dependent. After 28 days of leaching in deionized water, the LR Sr and LR Ln-average values for the n  = 5, 6, and 7 samples were 10 −4 –10 −3 and 10 −7 –10 −6 g·m −2 ·d −1 , respectively. Increasing configurational entropy in the high-entropy ( Ln 1/ n )PO 4 monazite phase indirectly reduced Sr release through phase-coupled effects, whereas average Ln release remained nearly unchanged.