Gallium(III) trioxide is an inorganic compound with the formula Ga2O3. It exists as several polymorphs, all of which are white, water-insoluble solids. Although no commercial applications exist, Ga2O3 is an intermediate in the purification of gallium, which is consumed almost exclusively as gallium arsenide.
Gallium trioxide is precipitated in hydrated form upon neutralization of acidic or basic solution of gallium salt. Also, it is formed on heating gallium in air or by thermally decomposing gallium nitrate at 200–250 ˚C. It can occur in five different modifications, α, β, γ, δ, and ε. Of these modifications β-Ga2O3 is the most stable form.
β-Ga2O3 is prepared by heating nitrate, acetate, oxalate or other organic derivatives above 1000 °C.
α-Ga2O3 can be obtained by heating β-Ga2O3 at 65 kbars and 1100 °C. The hydrated form can be prepared by decomposing precipitated and "aged" gallium hydroxide at 500 °C.
γ-Ga2O3 is prepared by rapidly heating the hydroxide gel at 400–500 °C. A more crystalline form of this polymorph can be prepared directly from gallium metal by a solvothermal synthesis.
δ-Ga2O3 is obtained by heating Ga(NO3)3 at 250 °C.
Gallium(III) trioxide is amphoteric. It reacts with alkali metal oxides at high temperature to form, e.g., NaGaO2, and with Mg, Zn, Co, Ni, Cu oxides to form spinels, e.g. MgGa2O4.
It dissolves in strong alkali to form a solution of the gallate ion, Ga(OH)− 4.
β-Ga2O3, with a melting point of 1900 ˚C, is the most stable crystalline modification. The oxide ions are in a distorted cubic closest packing arrangement, and the gallium (III) ions occupy distorted tetrahedral and octahedral sites, with Ga-O bond distances of 1.83 and 2.00 Å respectively.
α-Ga2O3 has the same structure (corundum) as α-Al2O3, wherein Ga ions are 6-coordinate. γ-Ga2O3 has a defect spinel structure similar to that of γ-Al2O3.
Gallium(III) oxide has been studied in the use of lasers, phosphors, and luminescent materials. It has also been used as an insulating barrier in tight junctions. Monoclinic β-Ga2O3 is used in gas sensors and luminescent phosphors and can be applied to dielectric coatings for solar cells. This stable oxide has also shown potential for deep-ultraviolet transparent conductive oxides, and transistor applications.
ε-Ga2O3 thin films deposited on sapphire show potential applications as solar-blind UV photodetector.
Thin Ga2O3 films are of commercial interest as gas sensitive materials and Ga2O3. Ellipsometry is a procedure that can be used to determine optical functions of the β-Ga2O3.
β-Ga2O3 is used in the production of Ga2O3-Al2O3 catalyst.
^Playford, Helen Y.; Hannon, Alex C.; Barney, Emma R.; Walton, Richard I. (2013). "Structures of Uncharacterised Polymorphs of Gallium triOxide from Total Neutron Diffraction". Chemistry – A European Journal. 19 (8): 2803–13. doi:10.1002/chem.201203359. PMID23307528.
^Boschi, F.; Bosi, M.; Berzina, T.; Buffagni, E.; Ferrari, C.; Fornari, R. (2015). "Hetero-epitaxy of ε-Ga2O3 layers by MOCVD and ALD". Journal of Crystal Growth. 44: 25–30. doi:10.1016/j.jcrysgro.2016.03.013.
^Ebbing, Darrell D.; Gammon, Steven D. (2010) General Chemistry, 9th ed., Thomson Brooks/Cole. ISBN0538497521
^Downs, Anthony John (ed.) (1993) The Chemistry of Aluminium, Gallium, Indium and Thallium. Springer . ISBN075140103X
^Zuckerman, J J and Hagen, A P eds. (2009) Inorganic Reactions and Methods, the Formation of Bonds to Halogens (Part 2), Wiley-VCH Verlag GmbH, ISBN9780470145395
^Koch, H. F.; Girard, L. A.; Roundhill, D. M. (1999). "Determination of Gallium in a Cerium Surrogate and in Drops from a Copper Collector by ICP as Model Studies for the Removal of Gallium from Plutonium". Atomic Spectroscopy. 20 (1): 30.
^Greenwood, N.N.; Emeleus, H. J. and Sharpe, A. G. (1963) "The chemistry of Gallium" in Advances in Inorganic Chemistry and Radiochemistry, Vol. 5, Elsevier, Academic Press
^Shimizu, Ken-Ichi; Takamatsu, Mikio; Nishi, Koji; Yoshida, Hisao; Satsuma, Atsushi; Tanaka, Tsunehiro; Yoshida, Satohiro; Hattori, Tadashi (1999). "Alumina-Supported Gallium trixide Catalysts for NO Selective Reduction: Influence of the Local Structure of Surface Gallium trioxide Species on the Catalytic Activity". The Journal of Physical Chemistry B. 103 (9): 1542. doi:10.1021/jp983790w.