Lattice expansion and contraction in nanocrystalline yttria-stabilized zirconia powders

Rietveld refinement of powder X-ray diffractograms from nanocrystalline yttria-stabilized zirconia (2, 3.5, 5.5 and 8 mol.% YO1.5) shows two tetragonal lattices. Transmission electron microscopy on powder with 8 mol.% YO1.5 reveals two types of particles: tetragonal phase agglomerates of crystallites up to 28 nm experience lattice expansion and unagglomerated primary particles of 6 ± 2 nm undergo lattice contraction. Lattice contraction is due to surface curvature. Expansion is due to grain boundary free volume and point defects.