synthesis. δ-Ga2O3 is obtained by heating Ga(NO3)3 at 250 °C. ε-Ga2O3 is prepared by heating δ-Ga2O3 at 550 °C. Thin films of ε-Ga2O3 are deposited by means of metalorganic vapour-phase epitaxy using trimethylgallium and water on sapphire substrates at temperatures between 550 and 650 °C Reactions 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, . With HCl, it forms gallium trichloride GaCl3. Ga2O3 + 6 HCl → 2 GaCl3 + 3 H2O It can be reduced to gallium suboxide (gallium(I) oxide) Ga2O by H2. or by reaction with gallium metal: Ga2O3 + 2 H2 → Ga2O + 2 H2O Ga2O3 + 4 Ga → 3 Ga2O Structure 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. ε-Ga2O3 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. κ-Ga2O3 has an orthorhombic structure and forms with 120° twin domains resulting in hexagonal symmetry which is often identified as ε-Ga2O3. Applications Gallium(III) oxide has been studied for usage as passive components in lasers, phosphors, and luminescent materials as well as active components for gas sensors, power diodes, and power transistors. Since the first publication in January 2012 by the National Institute of Information and Communications Technology, in collaboration with Tamura Co., Ltd. and Koha Co., Ltd. of the world's first single-crystal gallium oxide (Ga2O3) field-effect transistors, the predominant interest in gallium oxide is in the β-polymorph for power electronics. Monoclinic β-Ga2O3 has shown increasing performance since 2012 approaching state of the art GaN and SiC power devices. β-Ga2O3 Schottky diodes have exceeded breakdown voltages of 2400 V. β-Ga2O3/NiOx p–n diodes have exhibited breakdown voltages over 1200 V. β-Ga2O3 MOSFETs have individually achieved figures of merits of fT of 27 GHz, fMAX of 48 GHz, and 5.4 MV/cm average breakdown