Isotope effect on displacive-type ferroelectric-phase-transition temperatures

The isotope effect on the ferroelectric transition temperature ${\mathit{T}}_{\mathit{c}}$ is investigated within the polarizability model. The enhancement of any of the involved sublattice masses always yields an increase in ${\mathit{T}}_{\mathit{c}}$ and its magnitude is a function of ${\mathit{T}}_{\mathit{c}}$. While the increase in the rigid-ion mass only induces a small enhancement of ${\mathit{T}}_{\mathit{c}}$, the replacement of the nonlinearly polarizable unit by its isotope shows large effects for small transition temperatures and is zero for high ${\mathit{T}}_{\mathit{c}}$’s.