Ferroelectric domains and the condensed soft mode in gadolinium molybdate

Results of lattice dynamical calculations of the high temperature phase of gadolinium molybdate (GMO) support the view that the phase transition in GMO arises from a softening of a doubly degenerate zone edge mode. We find a close correlation between the displacements associated with these soft modes and the difference in the structure of the two phases, suggesting that, at the transition one or other set of soft mode displacements is ‘condensed’, or ‘frozen in’ to the structure. On this basis we can explain the ferroelectric switching.