An Abnormal Decrease in Curie Temperature in Pseudohalide Rare-Earth Double Perovskite Ferroelastics Driven by Lanthanide Contraction

Hybrid rare-earth double perovskites (HREDPs) have received increasing attention due to their structural tunability and multifunctionality. However, the impact of lanthanide contraction on the properties of HREDPs remains to be investigated. Herein, we synthesized a series of isostructural HREDP ferroelastics, (DMSOX)(2)LnCs(NO3)(6) (DMSOX = dimethylsulfoximine and Ln = La3+, Ce3+, Pr3+, Nd3+, Sm3+, and Eu3+). The results demonstrate that decreasing the rare-earth ionic radius modulates the Curie temperature (T-C), exhibiting a monotonic decrease from 411.1 to 395.8 K across the lanthanide series. Structural analysis reveals that the shrinkage of the ionic radius weakens hydrogen bonding interactions, which is the primary origin of the lowered T-C. Among them, Eu-based (DMSOX)(2)EuCs(NO3)(6) possesses an orange-red luminescence behavior with a lifetime of 4.87 ms and a quantum yield of 44%. This work provides a distinct strategy for fine-tuning multifunctional HREDP materials.