New Lead‐free Hybrid Layered Double Perovskite Halides: Synthesis, Structural Transition and Ultralow Thermal Conductivity

Hybrid layered double perovskites (HLDPs), representing the two-dimensional manifestation of halide double perovskites, have elicited considerable interest owing to their intricate chemical bonding hierarchy and structural diversity. This intensified interest stems from the diverse options available for selecting alternating octahedral coordinated trivalent M(III) and monovalent metal centers M(I), along with the distinctive nature of the cationic organic amine located between the layers. Here, we have synthesized three new compounds with general formula (R'/R'')