Compressibility and structural stability of nanoparticulate goethite

Synchrotron high-pressure X-ray diffraction was used to study the compressibility and structural stability of synthetic 17 nm nanoparticulate goethite at pressures up to ∼30 GPa. The lattice parameters and the unit cell volume were determined. We observed much higher contraction along c than a and b (Pnma space group), which we attribute to relatively weak hydrogen bonding along the c axis. In the hydrostatic pressure regime (pressures up to ∼10 GPa) the bulk modulus, K₀, of 17 nm goethite was determined to be 109.4 ± 2.2 GPa. The compressibility of the 17 nm goethite is comparable to that of the bulk goethite. Amorphization of the nano-goethite began at ∼17 GPa, an effect not observed in bulk goethite, even at much higher pressures. The findings indicate that for 17 nm particles, the size-dependence of goethite compressibility is small at low to moderate pressures, but at very high pressure, surface effects on nanoparticle structure become very significant.