Lattice Expansion in Metal Oxide Nanoparticles: MgO, Co 3 O 4 , & Fe 3 O 4

Uniform sets of mono‐crystalline nanoparticles ranging from 6 nm to over 100 nm were prepared for the MgO, Co 3 O 4 , and Fe 3 O 4 oxide systems. The nanoparticles were characterized by transmission electron microscopy ( TEM ) and x‐ray diffraction ( XRD ). A careful analysis shows increased lattice parameter for smaller nanoparticles of each oxide system: 0.47% expansion from bulk for 7 nm MgO crystallites, 0.15% expansion from bulk for 9 nm Co 3 O 4 crystallites, and 0.13% expansion from bulk for 6 nm Fe 3 O 4 crystallites. The compressive surface stresses and expansion energies against hydrostatic pressure for each oxide system were calculated, respectively, to be 4.13 N/m and 1.8 meV/formula unit for MgO, 3.09 N/m and 0.87 meV/formula unit for Co 3 O 4 , and 1.26 N/m and 0.67 meV/formula unit for Fe 3 O 4 . The fundamental understanding of oxide nanoparticle mechanics as presented here will facilitate integration of these materials into technological applications in a rationally designed manner.