Systematics of atomic displacement parameters in perovskite oxides

Atomic displacement parameters (ADPs) determined from crystal structure refinement principally embody atomic thermal vibration, but they can also include the effects of disorder, partial site occupancy, electronic interactions, and other factors. A growing number of consistently determined studies are becoming available from high T neutron powder diffraction instrumentation, making it possible in the near future to explore the systematic behavior of ADPs for chemically diverse and important classes of oxides such as the perovskites. Factors such as coordination number, formal valence, site symmetry, polyhedral volume, bond valence sum, electronegativity, temperature, atomic number, Debye temperature, phonon density of states and atomic size can be tested for significance. Ultimately, empirical rules and parameters to account for the systematic behavior can be developed, and then used as tools for studying new materials and identifying anomalous behavior.