High-temperature structural evolution of caesium and rubidium triiodoplumbates

Abstract CsPbI 3 and RbPbI 3 were investigated by in situ powder diffraction within temperature ranges of 298–687 K and 298–714 K, respectively. Both compounds crystallize in orthorhombic Pnma symmetry and expand isotropically upon a heating, revealing almost the same relative change of the lattice parameters. A pronounced difference in the structural evolution close to 600 K was observed, namely, CsPbI 3 undergoes first-order reversible phase transformation Pnma ⟷ 563 K Pnma + Pm 3¯ m ⟷ 602 K Pm 3¯ m , whereas no transitions (except of the sample's melting) in RbPbI 3 were detected. An attempt to clarify the relation between the existence/absence of a phase transition and bulging out of the iodine environment around alkaline ions was undertaken.