High-temperature structural evolution of caesium and rubidium triiodoplumbates

CsPbl(3) and RbPbl(3) were investigated by in situ powder diffraction within temperature ranges of 298-687K and 298-714K, 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 600K was observed namely, CsPbl(3) undergoes first-order reversible phase transformation Pnma <->(563K) Pnma+Pm (3) over barm <->(602K) Pm (3) over barm, whereas no transitions (except of the sample's melting) in RbPbl(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. (C) 2008 Elsevier Ltd. All rights reserved.