Precise measurement of equation-of-state and elastic properties for GaN up to 16 GPa

To determine the bulk modulus (B0) and its pressure derivative (B′0) of wurtzite-type GaN, the room temperature pressure (P)–volume (V) equation-of-state (EOS) is precisely measured up to 16 GPa by quasihydrostatic compression experiments with in situ energy-dispersive X-ray diffraction. In the present experiments we especially pay attention to the hydrostaticity of pressure conditions since previous studies implied that it largely affected to B0 and B′0. Nonhydrostatic effect is eliminated by enough annealing at each pressure. We find B0=202.4 GPa and B′0=4.5 by fitting to the third-order Birch–Murnaghan EOS. Though being different from the earlier experimental results using diamond-anvil cells, these values are quite concordant with recent data from Brillouin spectroscopies and ab initio calculations. Furthermore, we confirm that linear compressibilities (β) along a and c directions are almost same in GaN as βa=1.481×10−3 and βc=1.402×10−3, differing from other wurtzite-type group III nitrides. This corresponds to a small pressure dependence of the axial ratio c/a and the high ideality of the GaN lattice not only at ambient pressure but also under high pressures.