It has been demonstrated that electron microscope images obtained at about 3A resolution for Pr/sub 7/O/sub 12/ are in agreement with calculated images based upon known structures. This establishes the efficacy of crystal structure image interpretation in structural terms, including the defect structure and mechanism of phase reactions, for these types of related phases whose structures are as yet beyond conventional means to determine. Further work on the epsilon (Pr/sub 10/O/sub 18/) phase is reported both utilizing electron optical methods and single crystal X-ray techniques. The ternary ceramic system HfO/sub 2/.xEr/sub 2/O/sub 3/ is being examined using electron optical techniques and ordering not hitherto reported is being observed. An interactive crystal structure image calculation system is being developed which will permit the immediate comparison of enhanced images synthesized from trial structures (including defects) and displayed in juxtaposition on a graphics unit. 22 fig. (auth)