The measurement of internal strain in core-shell Ni3Si(Al)-SiOx nanoparticles

Internal defects and strain in nanoparticles can influence their properties and therefore measuring these values is relevant. Powder diffraction techniques (neutron and synchrotron) are successfully used to characterize internal strain in the core-shell Ni3Si(Al)-SiOx nanoparticles having mean diameters of ∼80 nm. The nanoparticles, which are strain-free after extraction from the bulk alloys, develop internal strain on heating. Both micro- and macro-strains can be measured from the analysis of Bragg peak shift and broadening. It is identified that differences in thermal expansion coefficient of the metallic core and the amorphous shell of the nanoparticles, as well as partial disordering of the L12 ordered core phase, are the main causes of strain evolution. Synchrotron measurements also detected partial crystallization of the amorphous silica shell.