Microstructural and thermodynamic study of γ-Ga₂O₃

Diffusion-driven and size-dependent phase changes of gallium oxide nanocrystals in a glassy host

“…25,26 g-Ga 2 O 3 irreversibly transforms into b-Ga 2 O 3 via a two step phase change involving an intermediate reversible change into a g 0 -Ga 2 O 3 phase. 27 d-Ga 2 O 3 was first observed as a result of heating of evaporated gallium nitrate solution at 470-520 K. 28 It was identified as a distinct polymorph with C-type rare earth sesquioxides, 28 but new recent data suggest that d-Ga 2 O 3 is probably a nanocrystalline form of e-Ga 2 O 3 and not a distinct polymorph. 19 This metastable phase in fact transforms into orthorhombic e-Ga 2 O 3 after heating above 770 K. Heating of e-Ga 2 O 3 above 1140 K eventually leads to stable b-Ga 2 O 3 .…”

Epitaxial growth of β-Ga2O3 nanocolumns on MgO substrate

“…The metastable g form grows epitaxially in order to reduce the misfit between the MgO substrate and Ga 2 O 3 . The g-Ga 2 O 3 crystal is metastable and the crystal sizes prepared by calcination process are very small [6,7]. However, a large single crystal film can be obtained on the MgO substrate.…”

“…The a form is metastable and has a hexagonal corundum structure with the lattice constant a ¼ 0:498 and c ¼ 1:343 nm, and the space group is R3c. The g-Ga 2 O 3 is isomorphic to g-Al 2 O 3 and has a cubic spinel structure (MgAl 2 O 4 -type) with the lattice constant a ¼ 0:822 nm, and the space group is Fd3m [5][6][7]. The metastable forms transform into the stable b form at 650 1C [7].…”

Thermodynamic assessment of the ternary systems Ga–Mg–O, Ga–Ni–O, Mg–Ni–O and extrapolation to the Ga–Mg–Ni–O phase diagram

“…The Gibbs energy function of ␥-Ga 2 O 3 ( • G GVV ) has recently been determined experimentally [8] and is used here without modification.…”

“…Lattice stabilities of the metastable ␣-, ␦-Ga 2 O 3 [7] and ␥-Ga 2 O 3 [8] were also assessed. At high temperatures, Ga-rich liquid reacts with ␤-Ga 2 O 3 to form Ga 2 O gas.…”