Size-Dependent Amorphization of Nanoscale ${\mathbf{Y}}_2{\mathbf{O}}_3$ at High Pressure

${\mathrm{Y}}_2{\mathrm{O}}_3$ with particle sizes ranging from 5 nm to $1\mu \mathrm{m}$ were studied at high pressure using x-ray diffraction and Raman spectroscopy techniques. Nanometer-sized ${\mathrm{Y}}_2{\mathrm{O}}_3$ particles are shown to be more stable than their bulk counterparts, and a grain size-dependent crystalline-amorphous transition was discovered in these materials. High-energy atomic pair distribution function measurements reveal that the amorphization is associated with the breakdown of the long-rang order of the ${\mathrm{YO}}_6$ octahedra, while the nearest-neighbor edge-shared octahedral linkages are preserved.

Figure 1

(a) Powder x-ray diffraction structure refinement of 16 nm-sized ${\mathrm{Y}}_2{\mathrm{O}}_3$; (cross: measured pattern; line: calculated pattern; black tick: position of peaks; line below tick: difference between calculated and measured patterns). (b) Dark field TEM image of ${\mathrm{Y}}_2{\mathrm{O}}_3$ with average particle size of 16 nm. (c) Lattice parameter as a function of particle size.

Figure 2

(a) X-ray diffraction patterns of 16 nm ${\mathrm{Y}}_2{\mathrm{O}}_3$ as a function of pressure, $\lambda =0.3691\acute{\AA }$. A broad peak at $2\theta \sim 7.7°$ and the gradual disappearance of the other diffraction peaks begin at $\sim 24\mathrm{GPa}$ and disappear by 32.7 GPa. (b) Patterns for 21 nm-sized ${\mathrm{Y}}_2{\mathrm{O}}_3$, $\lambda =0.3875\acute{\AA }$. The new peaks at $2\theta$ of 6.82° and 7.85° are indicated by red arrows.

Figure 3

(a) XRD patterns of 16 and 21 nm material in different pressure media under compression. (b) Raman spectra of pristine and pressure-released 16 nm ${\mathrm{Y}}_2{\mathrm{O}}_3$. The excitation laser wavelength was 514.5 nm.

Figure 4

(a) Pair distribution function (PDF) of 16 nm-sized ${\mathrm{Y}}_2{\mathrm{O}}_3$ at different pressures. The x-ray energy was 39.995 keV. Dashed lines are guides for the eye. (b) The structure model for the cubic structure of ${\mathrm{Y}}_2{\mathrm{O}}_3$. The distances between different atoms are shown with arrows, which correspond to each peak shown in (a). (c) Connections between the nearest octahedra. There is an unoccupied space among the six octahedra (inner and outer ones are not shown).