Simultaneous segregation of lanthanum to surfaces and grain boundaries in MgAl_2O_4 nanocrystals

摘要

The thermochemical stabilization of interfaces can improve properties of nanocrystalline oxides for applications under severe thermal stresses. This is achieved by using dopants (ionic additives) prone to interfacial segregation, causing local energy decrease and reducing coarsening driving forces. Here, we experimentally demon strate the spontaneous segregation of lanthanum (La) to the interfaces of MgAl2O4 nanocrystals. The segregation is shown to be dependent on interface-type, i.e. surfaces versus grain boundaries (solid-solid interfaces), with distinct energetic effects. By using calorimetric protocols, we demonstrate the surface energy of MgAl2O4 is lowered by the addition of La, with the effect of the dopant being crystallite size-dependent. Grain boundary energies did not show similar size dependency, which can be related to an early saturation of the interface by the dopant.