We are examining various perovskite solid solutions based on NaNbO3 or BiFeO3 that havepromising ferroelectric or multiferroic properties. All of these solid solutions show subtle phase boundaries as a function of composition, typically between phases which are very 'pseudo-cubic' but differ in important details (eg. lower symmetry and/or polarity) which dictate their ferroic properties. Unravelling these complexities requires neutron powder diffraction data of the highest resolution: our lab based PXRD data are not adequate to provide definitive structural models. The aim of this modest proposal is to analyse, in detail, selected compositions at and around these phase boundaries, in order toprovide a firm crystallographic basis for the understanding of the physical properties of these solid solutions