Solving Zeolite Structures Using Electron Crystallography

Recently we have performed a systematic quantitative analysis of crystal structure distortion for ~1300 ABX3 perovskites in terms of Ato B-site polyhedra volume ratios VA/VB [1].The analysis identified a number of compositions close to the boundary of perovskite type stability which we have studied experimentally by in situ highpressure synchrotron X-ray powder diffraction.Here we will present the results of these experiments for several materials studied under pressure for the first time and will discuss our theoretical and experimental findings focusing on the following aspects of perovskite (pv) and post-perovskite CaIrO3 (ppv) structure types: (1) interplay between geometry and symmetry in distorted perovskites (is there any intermediate phase between pv and ppv?); (2) topological and geometrical constraints for ABX3 stoichiometry (what might be the structure of hypothetical structure types denser than ppv?); and (3) the effect of vacancies in ABX3 and pressure-induced amorphization as an alternative to pv-ppv transition.