Emergence of a Relaxor Phase and Dimensional Tuning in Mixed 2D Hybrid Perovskites

High Resolution Image Download MS PowerPoint Slide Mixing of molecular cations in hybrid lead halide perovskites offers a powerful route to tailor their optoelectronic functionality, structural stability, and phase transition behavior. While such compositional engineering has been extensively studied in three-dimensional perovskites, its impact on low-dimensional analogues remains largely unexplored. Here, we investigate cation mixing in the Ruddlesden–Popper BA 2 MA n -1 Pb n Br 3 n +1 two-dimensional perovskites using a comprehensive multitechnique approach. We show that substituting methylammonium (MA) with dimethylammonium (DMA) transforms the long-range ferroelectric phase into a state characterized by frustrated electric dipoles. Broadband dielectric measurements reveal that this state is a relaxor phase, which was previously unobserved in three-dimensional hybrid perovskites. Remarkably, cation mixing also governs perovskite dimensionality, enabling stabilization of thick-slab members up to n = 5 in single-crystal form. These results establish cation mixing as a versatile tool for controlling both polar order and dimensionality in two-dimensional hybrid perovskites.