Role of molecular disorder in the loss of Ge long-range order

Determine whether increasing molecular disorder contributes to the abrupt loss of long-range Ge off-centering order in MAGeI3 and Ge-rich MAGe1−xSnxI3 compositions.

Background

The study finds that Ge-rich MAGe1−xSnxI3 exhibits strong long-range polar Ge off-centering, while methylammonium (MA) orientational order weakens progressively with increasing temperature. At the cubic transition, the long-range Ge displacement order drops abruptly and the Ge sublattice enters a dynamically disordered off-centering state. The observed correlation between the inorganic displacement pattern and MA orientations raises the unresolved question of whether the increasing molecular disorder actively drives or otherwise contributes to the loss of Ge long-range order, rather than merely occurring concurrently with it.