Pressure-Induced Structural Phase Transformation and Yield Strength of AlN

Abstract

Aluminum nitride, a significant ceramic material used in electronic technological applications, was investigated by in situ synchrotron radiation X-ray diffraction in a diamond anvil cell at ambient temperature. The starting sample of AlN powder with a 1–2 μm average grain size was compressed to 36.9 GPa under the hydrostatic condition and 36.2 GPa under the nonhydrostatic condition, respectively. The phase transformation from hexagonal wurtzite to cubic rock salt (B4-to-B1) for the hydrostatic condition 20.5 and 20.4 GPa for the nonhydrostatic condition. We found that the phase transition was irreversible and that pure cubic phase AlN was obtained after pressure relief to reestablish ambient pressure. The experimental results reveal that the bulk modulus of hexagonal AlN is B0 = 287.1 GPa at a fixed B0′ = 4 under hydrostatic compression. For the recompressed pure cubic sample in the diamond anvil, the equation of state (EOS) of cubic AlN is B0 = 357.0 GPa when fit from ambient pressure to 39.5 GPa. The h...