Compressibility of nanostructured alumina phases determined from synchrotron x-ray diffraction studies at high pressure

Abstract

Synchrotron x-ray diffraction studies up to pressures of 30 GPa have been performed on both nanostructured γ-Al2O3 and α-Al2O3. The P-V equation of state has been calculated from a fit to the diffraction data to obtain the compressibility for each of the compounds. The bulk modulus B0 of nanostructured γ-Al2O3 having grain-size diameters in the range 4 – 8 nm is B0 =152(8) GPa, appreciably lower than the value B0≈250 GPa of its bulk structural analog. The bulk-modulus of nanophase α-Al2O3 of 25 nm average crystallite diameter, which is difficult to stabilize at smaller dimensions because of thermodynamic considerations, is 252(9) GPa and therefore similar to that of bulk α-Al2O3. These studies suggest that only if the grain-size of alumina is below a critical value of several nanometers can substantial changes be expected in the isothermal bulk modulus compared to that of the isostructural bulk compound.

Effect of nanostructuration on compressibility of cubic BN

“…Our result confirms recent experimental [14,15] and theoretical [16][17][18] [19] and 34.5% [20], respectively). This can be attributed to the presence in nanocrystalline materials of a significant volume fraction of grain boundaries and triple junctions, which are more compressible than the crystalline grains.…”

Photoluminescence and transformation of dense Al2O3:Cr3+ condensates synthesized by laser-ablation route

“…The Birch-Murnaghan EOS of undoped g-Al 2 O 3 with specified size, i.e. B 0 ¼ 152 GPa for 4-8 nm [29], 172 GPa for 37 nm [30], and 250 GPa for bulk [29] assuming B 0 0 ¼ 4 for all cases, were then used for the residual stress calculation assuming negligible effect of minor Cr dopant on the EOS. The residual compressive stress turned out to be 2-3 GPa for the as-formed g-Al 2 O 3 :Cr 3+ condensates.…”

Particle-size effect on the compressibility of nanocrystalline alumina

“…25 Using x-ray diffraction, 20 nm particles of ␥ alumina have been studied up to 3.8 GPa, and 6 nm particles have been studied up to 30 GPa. 26,27 No new phases were observed and equations of state were obtained for both sizes of particles. In the present article, we report on x-ray diffraction experiments performed up to a pressure of 60 GPa to measure the compressibility of nanocrystalline ␥-Al 2 O 3 as a function of particle size.…”