Incipient geometric lattice instability of cubic fluoroperovskites

Metal halide perovskites are promising materials for modern technologies with unique physical properties. In particular, search and investigation for ferroelectricity and multiferroicity in them are very active research topics. Here, the authors study the lattice dynamics of cubic fluoroperovskites $A\phantom{\rule{0}{0ex}}M$F${}_{3}$, and show that these materials exhibit affinity to incipient ferroelectrics, which manifests itself in the softening of polar phonons. The value of this softening correlates with the perovskite tolerance factor $t$, which speaks for the geometric origin of the observed effect.