Isotopes in neutron diffraction: Detailed structural analysis at the metal-insulator transition in SmNiO3

The use of isotopically enriched materials on high intensity neutron powder diffractometers allows the derivation of much higher quality structural information than has hitherto been possible. The technique can be applied to materials such as ferroelectrics, superconductors and oxides exhibiting colossal magneto-resistance, where small structural changes associated with phase transitions need to be characterised. Three isotopically pure samples of samarium nickelate have been studied around the metal-insulator transition at 403 K. Simultaneous multi-histogram refinements permit extraction of very high quality structural information that shows smooth variations in bond lengths and angles with all nickel oxygen distances decreasing as the electrons localise.