Ferroelectricity in the Dion-Jacobson (DJ) family of layered perovskites arises from a 'trilinear coupling', whereby two non-polar lattice modes interact in such a way to cooperate with a 3rd, polar mode. These systems are gaining in interest as the predicted (and now observed) polariations are typically larger than those in the related families of layered perovskites. In a previous VT HRPD study (RB1520003) we carried out detaled measurements of the structural evolution of two members of this family, CsLaNb2O7 and CsBi0.6La0.4Nb2O7, at sub-ambient and above-ambient, respectively. The aim of the present proposal is to complete our analysis of this system by collecting data on the two end-member compositions CsLaNb2O7 and CsBiNb2O7 above RT, and through the ferroelectric-paraelectric transition. The results are urgently required as a comparision to a recent synchrotron study of CsLaNb2O7