Gallium(III) oxide Gallium trioxide is an inorganic compound with the formula Ga2 O3 . It exists as several polymorphs , all of which are white, water-insoluble solids. Although no commercial applications exist, Ga2 O3 is an intermediate in the purification of gallium, which is consumed almost exclusively as gallium arsenide .Preparation 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-Ga2 O3 is the most stable form. β-Ga2 O3 is prepared by heating nitrate, acetate, oxalate or other organic derivatives above 1000 °C. α-Ga2 O3 can be obtained by heating β-Ga2 O3 at 65 kbars and 1100 °C. The hydrated form can be prepared by decomposing precipitated and "aged" gallium hydroxide at 500 °C. γ-Ga2 O3 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-Ga2 O3 is obtained by heating Ga3 at 250 °C. ε-Ga2 O3 is prepared by heating δ-Ga2 O3 at 550 °C. Thin films of ε-Ga2 O3 are deposited by means of Metalorganic vapour phase epitaxy using Trimethylgallium and water on sapphire substrates at temperatures between 550 and 650 °CReactions Gallium 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. MgGa2 O4 . It dissolves in strong alkali to form a solution of the gallate ion,. With HCl, it forms gallium trichloride GaCl3 . It can be reduced to gallium suboxide Ga2 O by H2 . or by reaction with gallium metal:Structure β-Ga2 O3 , 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 ions occupy distorted tetrahedral and octahedral sites, with Ga-O bond distances of 1.83 and 2.00 Å respectively. α-Ga2 O3 has the same structure as α-Al2 O3 , wherein Ga ions are 6-coordinate. γ-Ga2 O3 has a defect spinel structure similar to that of γ-Al2 O3 . ε-Ga2 O3 films deposited by metalorganic vapour phase epitaxy show a columnar structure with orthorhombic crystal symmetry . Macroscopically, this structure is seen by X-ray crystallography as hexagonal close packed .Potential applications Gallium 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-Ga2 O3 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-Ga2 O3 thin films deposited on sapphire show potential applications as solar-blind UV photodetector . Thin Ga2 O3 films are of commercial interest as gas sensitive materials and Ga2 O3 . Ellipsometry is a procedure that can be used to determine optical functions of the β-Ga2 O3 . β-Ga2 O3 is used in the production of Ga2 O3 -Al2 O3 catalyst.
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