Probing the short-range order and dynamics of phase transitions using neutron powder diffraction

We report evidence that the local structure of the perovskite based material, La2-xBaxCuO4, is disordered. The disorder takes the form of inhomogeneous octahedral tilts. The average crystal structure is a superposition of the local tilting environments. The local symmetry is different from the average, long-range order, and local bond lengths deviate from those obtained from the crystallographic coordinates. This has implications for band structure calculations based on the crystallographic coordinates. We discuss the implications of the local structure for understanding the microscopic origin for the phase transitions in this material. The evidence presented is from neutron powder diffraction data analyzed using the pair distribution function method. We describe this method and mention possible extensions to this method For extracting local dynamics at phase transitions.