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.

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Critical currents of YBaCuO ceramics were measured at 77 K by transport measurements in an applied magnetic field H. A hysteretic behavior between 10 and 10 000 G was observed. For decreasing fields, the critical current Jc obeys a power law H−n with n ranging between 0.6 and 2.8. The exponent n is correlated with the microstructure and the average grain size of the ceramic. This power law behavior is discussed in terms of modified flux creep and flux flow regimes related to the microstructure.

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