Gallium(III) oxide

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Gallium(III) oxide
Identifiers
CAS number 12024-21-4 YesY
PubChem 5139834
ChemSpider 4313617 YesY
RTECS number LW9650000
Jmol-3D images Image 1
Properties
Molecular formula Ga2O3
Molar mass 187.444 g/mol
Appearance white crystalline powder
Density 6.44 g/cm3, alpha
5.88 g/cm3, beta
Melting point 1900 °C, alpha
1725 °C, beta [1]
Solubility in water insoluble
Solubility soluble in most acids
Hazards
EU classification not listed
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Gallium(III) oxide (Ga2O3) is a chemical compound used in vacuum deposition and as part of the manufacturing of semiconductor devices.[2]

Preparation[edit]

Gallium oxide 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,δ,γ and ε. Of these modifications β-Ga2O3 is the most stable form.[3]

Preparation Methods for the Five Modifications[edit]

  • 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 65kbars and 1100˚C for 1 hour giving a crystalline structure. 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˚C-500˚C. A more crystalline form of this polymorph can be prepared directly from gallium metal by a solvothermal synthesis.[4]
  • δ-Ga2O3 is obtained by heating Ga(NO3)3 at 250˚C.
  • ε-Ga2O3 is prepared by briefly heating δ-Ga2O3 at 550˚C for 30 minutes.[3]

Reactions[edit]

Gallium(III) oxide is amphoteric.[5] reacting 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.[6] and dissolving in strong alkali to form a solution of the gallate ion, Ga(OH)
4
.

With HCl gas under argon it forms gallium trichloride GaCl3.[7]

Ga2O3 + 6 HCl → GaCl3 + H2O

It can be reduced to gallium suboxide, (gallium(I) oxide), Ga2O by H2,[8] or by reaction with gallium metal[9]

Ga2O3 + H2 → Ga2O + H2O
Ga2O3 + 4 Ga → 3 Ga2O

Crystal Structure[edit]

β-Ga2O3, with a melting point of 1740˚C, is the most stable crystalline modification. The oxide ions are in a distorted cubic closest packing arrangement, and the gallium (III) ions are in distorted tetrahedral and octahedral sites, with Ga-O bond distances of 1.83 and 2.00 Å respectively. These distortions are in fact the reasons for the great level of stability of β-Ga2O3.[10]

α-Ga2O3 has the same structure (corundum) as α-Al2O3 where all Ga atoms are 6 coordinate. γ-Ga2O3 has a defect spinel structure similar to that of γ-Al2O3[11]

Applications and Uses[edit]

Gallium(III) oxide is an important functional material. It has been studied in the use of lasers, phosphors and luminescent materials,[12] has been shown to demonstrate catalytic properties and has also been used as an insulating barrier in tight junctions.[13] The stable oxide of gallium, monoclinic β-Ga2O3, has current applications 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.[14]

Nanotechnology[edit]

Nanoribbons and nanosheets of Ga2O3 can be synthesized either by high temperature reaction of Ga0 with water or by evaporation of GaN at high temperature in the presence of oxygen. Analysis of the products of the thermal evaporation reaction is done using X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS). Such analysis showed that the resulting structures were wool-like.

SEM reveals that the products consist of wire-like nanostructures and sheet-type structures. The TEM image shows the ribbon-like structure of Ga2O3. The EDS confirms that the nanostructures obtained are in fact Ga2O3.

The nanoribbon and nanosheets structures of Ga2O3 are pure, structurally uniform, single crystalline and free from dislocation. The structure of nanoribbons and nanosheets, that is, their wave-like and sheet-like shape, also indicates that their growth is as a result of growth kinetics, vapor-liquid-solid (VLS) method and vapor-solid method (VS). VLS and VS are two common growth mechanisms for nanowires. The VLS process, catalytic-assisted in nature, is one in which the metal particle is located at the growth of the wire and acts as the catalytic active site. For the VS process, oxide vapor, which is evaporated from the starting oxide at a higher temperature xone, directly deposits on a substrate at a lower temperature region and grows into ribbon-like nanostructures.[13]

Optical Uses[edit]

It is important to accurately determine the optical functions as these are essential for device simulations and improvement in material preparation. The thin Ga2O3 films are of commercial interest as gas sensitive material and Ga2O3 based glasses are among the best optical materials used in advanced technologies. Ellipsometry is a procedure that can be used to determine optical functions of the β-Ga2O3.[14]

Catalyst[edit]

β-Gallium(III) oxide is also very important in the production of catalysts. It is needed for the preparation of Ga2O3-Al2O3 catalyst. The preparation of this catalyst involves reacting Al2O3 with aqueous solutions of gallium nitrate, followed by evaporation to dryness at 393K, and calcining in air (i.e.thermal decomposition of the compound) for 4 hours at 823K.[15]

See also[edit]

References[edit]

  1. ^ Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0-07-049439-8
  2. ^ "Gallium oxide powder (Ga2O3)". READE Advanced Materials. Retrieved 8 November 2009. 
  3. ^ a b Bailar, J; Emeléus, H; Nyholm, R; Trotman-Dickenson, A. Comprehensive Inorganic Chemistry. 1973, 1, 1091
  4. ^ Playford, H. Y; Hannon, A. C; Barney, E. R; Walton, R. I. Chem. Eur. J. 2013, 19, 2803
  5. ^ General Chemistry, 9th Enhanced edition, Darrell D. Ebbing, Steven D. Gammon, Thomson Brooks/Cole 2010,ISBN 0538497521, ISBN 978-0538497527
  6. ^ The Chemistry of Aluminium, Gallium, Indium and Thallium, Anthony John Downs, 1993, ISBN 075140103X , ISBN 978-0751401035
  7. ^ Inorganic Reactions and Methods, the Formation of Bonds to Halogens (Part 2), J J Zuckerman, Ed: A P Hagen, eBook, 17 September 2009, Wiley-VCH Verlag GmbH, ISBN 9780470145395
  8. ^ 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, HF Koch, LA Girard, DM Roundhill - ATOMIC SPECTROSCOPY, 1999, vol 20, 1, 30
  9. ^ ADVANCES IN INORGANIC CHEMISTRY AND RADIOCHEMISTRY, Volume 5, The chemistry of Gallium, N.N. Greenwood, ED H. J. Emeleus, A. G. Sharpe 1963, Elsevier, Academic Press
  10. ^ King, R; Encyclopedia of Inorganic Chemistry. 1994, 3, 1256
  11. ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 247. ISBN 0080379419. 
  12. ^ Bailar, J; Emeléus, H; Nyholm, R; Trotman-Dickenson, A. Comprehensive Inorganic Chemistry. 1973, 1, 1091.
  13. ^ a b Dai, Z; Pan, Z; Wang, Z. J. Phys. Chem. B. 2002, 106, 902.
  14. ^ a b Rebien, M; Henrion, W; Hong, M; Mannaerts, J; Fleischer, M. Applied Physics Letters. 2002, 81, 250.
  15. ^ Shimizu, K; Takamatsu, M; Nishi, K; Yoshida, H; Satsuma, A; Tanaka, T; Yoshida, S; Hattori, T. J. Phys. Chem. 1999. 103, 1543.