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

Synchrotron x-ray diffraction studies up to pressures of 30 GPa have been p erformed on both nanostructured gamma -Al2O3 and alpha -Al2O3. The P-V equa tion of state has been calculated from a fit to the diffraction data to obt ain the compressibility for each of the compounds. The bulk modulus B-0 of nanostructured gamma -Al2O3 having grain-size diameters in the range 4 - 8 nm is B-0 =152(8) GPa, appreciably lower than the value B(0 approximate to) 250 GPa of its bulk structural analog. The bulk-modulus of nanophase alpha -Al2O3 of 25 nm average crystallite diameter, which is difficult to stabili ze at smaller dimensions because of thermodynamic considerations, is 252(9) GPa and therefore similar to that of bulk alpha -Al2O3. These studies sugg est that only if the grain-size of alumina is below a critical value of sev eral nanometers can substantial changes be expected in the isothermal bulk modulus compared to that of the isostructural bulk compound. (C) 2001 Ameri can Institute of Physics.