Tantalum pentoxide

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Tantalum pentoxide

  Ta   O
Names
IUPAC name
Tantalum(V) oxide
Systematic IUPAC name
Ditantalum pentaoxide
Identifiers
3D model (
JSmol
)
ChemSpider
ECHA InfoCard
 100.013.854 Edit this at Wikidata
UNII
  • InChI=1S/5O.2Ta
  • O=[Ta](=O)O[Ta](=O)=O
Properties
Ta2O5
Molar mass 441.893 g/mol
Appearance white, odorless powder
Density β-Ta2O5 = 8.18 g/cm3[1]
α-Ta2O5 = 8.37 g/cm3
Melting point 1,872 °C (3,402 °F; 2,145 K)
negligible
Solubility insoluble in organic solvents and most mineral acids, reacts with HF
Band gap 3.8–5.3 eV
−32.0×10−6 cm3/mol
2.275
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Tantalum pentoxide, also known as

dielectric constant
.

Preparation

Occurrence

Tantalum occurs in the minerals tantalite and columbite (columbium being an archaic name for niobium), which occur in pegmatites, an igneous rock formation. Mixtures of columbite and tantalite are called coltan. Tantalite was discovered by Anders Gustaf Ekeberg[when?] at Ytterby, Sweden, and Kimoto, Finland. The minerals microlite and pyrochlore contain approximately 70% and 10% Ta, respectively.

Refining

Tantalum ores often contain significant amounts of niobium, which is itself a valuable metal. As such, both metals are extracted so that they may be sold. The overall process is one of hydrometallurgy and begins with a leaching step; in which the ore is treated with hydrofluoric acid and sulfuric acid to produce water-soluble hydrogen fluorides, such as the heptafluorotantalate. This allows the metals to be separated from the various non-metallic impurities in the rock.

(FeMn)(NbTa)2O6 + 16 HF → H2[TaF7] + H2[NbOF5] + FeF2 + MnF2 + 6 H2O

The tantalum and niobium hydrogenflorides are then removed from the

organic solvents, such as cyclohexanone or methyl isobutyl ketone. This step allows the simple removal of various metal impurities (e.g. iron and manganese) which remain in the aqueous phase in the form of fluorides. Separation of the tantalum and niobium is then achieved by pH
adjustment. Niobium requires a higher level of acidity to remain soluble in the organic phase and can hence be selectively removed by extraction into less acidic water. The pure tantalum hydrogen fluoride solution is then neutralised with aqueous
hydrated tantalum oxide (Ta2O5(H2O)x), which is calcinated to tantalum pentoxide (Ta2O5) as described in these idealized equations:[3]

H2[TaF7] + 5 H2O + 7 NH3 → 1/2 Ta2O5(H2O)5 + 7 NH4F
Ta2O5(H2O)5 → Ta2O5 + 5 H2O

Natural pure tantalum oxide is known as the mineral tantite, although it is exceedingly rare.[4]

From alkoxides

Tantalum oxide is frequently used in electronics, often in the form of

MOCVD (or related techniques), which involves the hydrolysis of its volatile halides or alkoxides
:

Ta2(OEt)10 + 5 H2O → Ta2O5 + 10 EtOH
2
TaCl5
+ 5 H2O → Ta2O5 + 10 HCl

Structure and properties

The crystal structure of tantalum pentoxide has been the matter of some debate. The bulk material is

Xray crystallography has largely been limited to powder diffraction
, which provides less structural information.

At least 2

orthorhombic in both cases, with the space group of β-Ta2O5 being identified as Pna2 by single crystal X-ray diffraction.[8]
A high pressure form (Z-Ta2O5) has also been reported, in which the Ta atoms adopt a 7 coordinate geometry to give a
monoclinic structure (space group C2).[9]

Purely amorphous tantalum pentoxide has a similar local structure to the crystalline polymorphs, built from TaO6 and TaO7 polyhedra, while the molten liquid phase has a distinct structure based on lower coordination polyhedra, mainly TaO5 and TaO6.[10]

The difficulty in forming material with a uniform structure has led to variations in its reported properties. Like many metal oxides Ta2O5 is an

amorphous
the material the greater its observed band gap. These observed values are significantly higher than those predicted by computational chemistry (2.3 - 3.8 eV).[14][15][16]

Its

high-k dielectric
material.

Reactions

Ta2O5 does not react appreciably with either HCl or HBr, however it will dissolve in hydrofluoric acid, and reacts with potassium bifluoride and HF according to the following equation:[19][20]

Ta2O5 + 4 KHF2 + 6 HF → 2 K2[TaF7] + 5 H2O

Ta2O5 can be reduced to metallic Ta via the use of metallic reductants such as calcium and aluminium.

Ta2O5 + 5 Ca → 2 Ta + 5 CaO
Several 10 μF × 30 V DC rated tantalum capacitors, solid-bodied epoxy-dipped type. Polarity is explicitly marked.

Uses

In electronics

Owing to its high

DRAM capacitor applications.[21][22]

It is used in on-chip metal-insulator-metal capacitors for high frequency CMOS integrated circuits. Tantalum oxide may have applications as the charge trapping layer for non-volatile memories.[23][24] There are applications of tantalum oxide in resistive switching memories.[25]

In optics

Due to its high

photographic lenses.[2][26]
It can also be deposited as an optical coating with typical applications being antireflection and multilayer filter coatings in near UV to near infrared. [27]

Ta2O5 has also been found to have a high nonlinear refractive index,[28][29] on the order of three times that of silicon nitiride, which has led to interest in the utilization of Ta2O5 in photonic integrated circuits. Ta2O5 has been recently utilized as the material platform for the generation of supercontinuum[30][31] and Kerr frequency combs[29] in waveguides and optical ring resonators. Through the addition of rare-earth dopants in the deposition process, Ta2O5 waveguide lasers have been presented for a variety of applications, such as remote sensing and LiDAR.[32][33][34]

References

  1. doi:10.1021/ja01599a003
    .
  2. ^
    ISBN 978-0-444-40205-9
    .
  3. ISBN 9780080529028
    .
  4. ^ "Tantite: Tantite mineral information and data". Mindat.org. Retrieved 2016-03-03.
  5. ^
    doi:10.1016/j.jssc.2003.07.003
    .
  6. doi:10.1107/S056774087100342X
    .
  7. ^ Wells, A.F. (1947). Structural Inorganic Chemistry. Oxford: Clarendon Press.
  8. doi:10.1524/zkri.1969.129.5-6.365
    .
  9. S2CID 22330435
    .
  10. doi:10.1103/PhysRevMaterials.2.043602
    .
  11. doi:10.1016/0040-6090(94)06388-5
    .
  12. doi:10.1063/1.373747
    .
  13. S2CID 97813703
    .
  14. doi:10.1063/1.1615700
    .
  15. doi:10.1063/1.370831
    .
  16. PMID 23243661
    .
  17. doi:10.1016/0368-1874(84)83577-7
    .
  18. doi:10.1063/1.1509861
    .
  19. doi:10.1016/S0022-1139(03)00190-8
    .
  20. ISBN 978-0-12-395591-3
    .
  21. ^ Ezhilvalavan, S.; Tseng, T. Y. (1999). "Preparation and properties of tantalum pentoxide (Ta2O5) thin films for ultra large scale integrated circuits (ULSIs) application - a review". Journal of Materials Science: Materials in Electronics. 10 (1): 9–31.
    S2CID 55644772
    .
  22. ^ Chaneliere, C; Autran, J L; Devine, R A B; Balland, B (1998). "Tantalum pentoxide (Ta2O5) thin films for advanced dielectric applications". Materials Science and Engineering: R. 22 (6): 269–322.
    doi:10.1016/S0927-796X(97)00023-5
    .
  23. ^ Wang, X; et al. (2004). "A Novel MONOS-Type Nonvolatile Memory Using High-κ Dielectrics for Improved Data Retention and Programming Speed". IEEE Transactions on Electron Devices. 51 (4): 597–602.
    doi:10.1109/TED.2004.824684
    .
  24. ^ Zhu, H; et al. (2013). "Design and Fabrication of Ta2O5 Stacks for Discrete Multibit Memory Application". IEEE Transactions on Nanotechnology. 12 (6): 1151–1157.
    S2CID 44045227
    .
  25. ^ Lee, M-.J; et al. (2011). "A fast, high-endurance and scalable non-volatile memory device made from asymmetric Ta2O5−x/TaO2−x bilayer structures".
    PMID 21743450
    .
  26. ISBN 978-0-8247-7309-0
    .
  27. ^ "Tantalum Oxide for Optical Coating Applications". Materion. Retrieved April 1, 2021.
  28. PMID 19484065
    .
  29. ^
    S2CID 220793938
    .
  30. PMID 33115180
    .
  31. PMID 33846403
    .
  32. ISSN 2159-3930
    .
  33. ISSN 1742-6596
    .
  34. S2CID 28849615
    .
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