In chemistry, molybdenum bronze is a generic name for certain mixed oxides of molybdenum with the generic formula A
xMo
yO
z where A may be hydrogen, an alkali metal cation (such as Li+, Na+, K+), and Tl+. These compounds form deeply coloured plate-like crystals with a metallic sheen, hence their name. These bronzes derive their metallic character from partially occupied 4d bands.[1] The oxidation states in K0.28MoO3 are K+1, O2−, and Mo+5.72. MoO3 is an insulator, with an unfilled 4d band.

These compounds have been much studied since the 1980s due to their markedly anisotropic electrical properties, reflecting their layered structure. The electrical resistivity can vary considerably depending on the direction, in some cases by 200:1 or more. They are generally non-stoichiometric compounds. Some are metals and some are semiconductors.

Preparation

The first report of a "molybdenum bronze" was by Alfred Stavenhagen and E. Engels in 1895. They reported that electrolysis of molten Na
2MoO
4 and MoO
3 gave indigo-blue needles with metallic sheen, which they analysed by weight as Na
2Mo
5O
7.[2] The first unambiguous synthesis of alkali molybdenum bronzes was reported only in 1964, by Wold and others.[3] They obtained two potassium bronzes, "red" K
0.26MoO
3 and "blue" K
0.28MoO
3, by electrolysis of molten K
2MoO
4+MoO
3 at 550 °C and 560 °C, respectively. Sodium bronzes were also obtained by the same method. It was observed that at a slightly higher temperature (about 575 °C and above) only MoO
2 is obtained.[3][4]

Another preparation technique involves crystallization from the melt in a temperature gradient. This report also called attention to the marked anisotropic resistivity of the purple lithium bronze Li
0.9Mo
6O
17 and its metal-to-insulator transition at about 24 K.[5]

Hydrogen bronzes H
xMoO
3 were obtained in 1950 by Glemser and Lutz, by ambient-temperature reactions.[6] The hydrogen in these compounds can be replaced by alkali metals by treatment with solutions of the corresponding halides. Reactions are conducted in an autoclave at about 160 °C.[7]

Crystals of K0.28MoO3, also called "potassium-molybdenum blue bronze".

Classification

Molybdenum bronzes are classified in three major families:[4][7]

  • Red bronzes with limiting composition A
    0.33    MoO
    3    , that is, AMo
    3    O
    9    :[7]
    • Lithium molybdenum red bronze Li
      0.33      MoO
      3       Reau and others.[7][8]
    • Potassium molybdenum red bronze K
      0.26      Mo
      1.02      O
      3      [3] or K
      0.3      MoO
      3      [8][9]
    • Cesium molybdenum red bronze Cs
      0.33      MoO
      3      [8]
    • Potassium molybdenum red bronze K
      0.23      Mo
      1.01      O
      3       a semi-conductor.[3]
  • Blue bronzes, with limiting composition A
    0.30    MoO
    3    , that is, A
    3    Mo
    10    O
    30    .[7] Their electronic properties generally do not depend on the metal A.[1]
    • Potassium molybdenum blue bronze K
      0.28      Mo
      1.02      O
      3      [3] or K
      0.3      MoO
      3      [8][9]
    • Rubidium molybdenum blue bronze Rb
      0.3      MoO
      3      [3][9]
    • Thallium molybdenum blue bronze Tl
      0.3      MoO
      3      [10]
  • Purple bronzes, generally with limiting formula A
    0.9    Mo
    6    O
    17    . Their electronic properties depend strongly on the metal A.[1]
    • Lithium molybdenum purple bronze Li
      0.9      Mo
      6      O
      17
    • Sodium molybdenum purple bronze Na
      0.9      Mo
      6      O
      17
    • Potassium molybdenum purple bronze K
      0.9      Mo
      6      O
      17
    • Rubidium molybdenum purple bronze Rb
      0.9      Mo
      6      O
      17
    • Thallium molybdenum purple bronze Cs
      0.9      Mo
      6      O
      17      [11]

The hydrogen molybdenum bronzes have similar appearances but different compositions:

  • Hydrogen molybdenum orthorhombic blue bronze H
    x    MoO
    3    , 0.23 < x < 0.4 [12]
  • Hydrogen molybdenum monoclinic blue bronze H
    x    MoO
    3    , 0.85 < x < 1.4 [12]
  • Hydrogen molybdenum red bronze H
    x    MoO
    3    , 1.55 < x < 1.72 [12]
  • Hydrogen molybdenum green bronze H
    2    MoO
    3     or MoO
    2    .H
    2    O     [6][12]

Other molybdenum bronzes with anomalous electrical properties have been reported, which do not fit in these families. These include

Electrical and thermal properties

See also

References

  1. 1 2 3 Onoda, M.; Toriumi, K.; Matsuda, Y.; Sato, M. (1987). "Crystal structure of lithium molybdenum purple bronze Li0.9Mo6O17". Journal of Solid State Chemistry. Elsevier BV. 66 (1): 163–170. Bibcode:1987JSSCh..66..163O. doi:10.1016/0022-4596(87)90231-3. ISSN 0022-4596.
  2. ↑ Stavenhagen, A.; Engels, E. (1895). "Ueber Molybdänbronzen". Berichte der Deutschen Chemischen Gesellschaft. Wiley. 28 (2): 2280–2281. doi:10.1002/cber.189502802213. ISSN 0365-9496.
  3. 1 2 3 4 5 6 Wold, A.; Kunnmann, W.; Arnott, R. J.; Ferretti, A. (1964). "Preparation and Properties of Sodium and Potassium Molybdenum Bronze Crystals". Inorganic Chemistry. American Chemical Society (ACS). 3 (4): 545–547. doi:10.1021/ic50014a022. ISSN 0020-1669.
  4. 1 2 Martha Greenblatt (1996), "Molybdenum and tungsten bronzes: Low-dimensional metals with unisial properties". In C. Schlenker ed., "Physics and Chemistry of Low-Dimensional Inorganic Conductors" Book, Springer, 481 pages. ISBN 9780306453045
  5. ↑ Greenblatt, M.; McCarroll, W.H.; Neifeld, R.; Croft, M.; Waszczak, J.V. (1984). "Quasi two-dimensional electronic properties of the lithium molybdenum bronze, Li0.9Mo6O17". Solid State Communications. Elsevier BV. 51 (9): 671–674. Bibcode:1984SSCom..51..671G. doi:10.1016/0038-1098(84)90944-x. ISSN 0038-1098.
  6. 1 2 Glemser, Oskar; Lutz, Gertrud (1950). "Über ein Hydroxydhydrid des Molybdäns". Die Naturwissenschaften (in German). Springer Science and Business Media LLC. 37 (23): 539–540. Bibcode:1950NW.....37..539G. doi:10.1007/bf00589341. ISSN 0028-1042. S2CID 46699509.
  7. 1 2 3 4 5 Chin, Kin; Eda, Kazuo; Sotani, Noriyuki; Whittingham, M.Stanley (2002). "Hydrothermal Synthesis of the Blue Potassium Molybdenum Bronze, K0.28MoO3". Journal of Solid State Chemistry. Elsevier BV. 164 (1): 81–87. Bibcode:2002JSSCh.164...81C. doi:10.1006/jssc.2001.9450. ISSN 0022-4596.
  8. 1 2 3 4 Tsai, P.P.; Potenza, J.A.; Greenblatt, M.; Schugar, H.J. (1986). "Crystal structure of Li0.33MoO3, a stoichiometric, triclinic, lithium molybdenum bronze". Journal of Solid State Chemistry. Elsevier BV. 64 (1): 47–56. Bibcode:1986JSSCh..64...47T. doi:10.1016/0022-4596(86)90120-9. ISSN 0022-4596.
  9. 1 2 3 Whangbo, M. H.; Schneemeyer, L. F. (1986). "Band electronic structure of the molybdenum blue bronze A0.30MoO3 (A = K, Rb)". Inorganic Chemistry. American Chemical Society (ACS). 25 (14): 2424–2429. doi:10.1021/ic00234a028. ISSN 0020-1669.
  10. ↑ Collins, B.T.; Ramanujachary, K.V.; Greenblatt, M.; Waszczak, J.V. (1985). "Charge-density wave instability and nonlinear transport in Tl0.3MoO3 a new blue molybdenum oxide bronze". Solid State Communications. Elsevier BV. 56 (12): 1023–1028. Bibcode:1985SSCom..56.1023C. doi:10.1016/0038-1098(85)90863-4. ISSN 0038-1098.
  11. ↑ E. Canadell and M.-H. Wangbo (1996), "Fermi surfaces instabilities in oxides and bronzes". In C. Schlenker ed. (1996), "Physics and Chemistry of Low-Dimensional Inorganic Conductors" Book, Springer, 481 pages. ISBN 9780306453045
  12. 1 2 3 4 Birtill, J.J.; Dickens, P.G. (1979). "Thermochemistry of hydrogen molybdenum bronze phases HxMoO3". Journal of Solid State Chemistry. Elsevier BV. 29 (3): 367–372. Bibcode:1979JSSCh..29..367B. doi:10.1016/0022-4596(79)90193-2. ISSN 0022-4596.
  13. ↑ Ramanujachary, K.V.; Greenblatt, D.M.; Jones, E.B.; McCarroll, W.H. (1993). "Synthesis and Characterization of a New Modification of the Quasi-Low-Dimensional Compound KMo4O6". Journal of Solid State Chemistry. Elsevier BV. 102 (1): 69–78. Bibcode:1993JSSCh.102...69R. doi:10.1006/jssc.1993.1008. ISSN 0022-4596.
  14. ↑ Andrade, Margareth; Maffei, Mariana Lanzoni; Alves, Leandro Marcos Salgado; Santos, Carlos Alberto Moreira dos; Ferreira, Bento; Sartori, Antonio Fernando (2012-10-11). "Microstructure and metal-insulator transition in single crystalline KMo4O6". Materials Research. FapUNIFESP (SciELO). 15 (6): 998–1002. doi:10.1590/s1516-14392012005000132. ISSN 1980-5373.
  15. ↑ Alves, L. M. S.; Damasceno, V. I.; dos Santos, C. A. M.; Bortolozo, A. D.; Suzuki, P. A.; Izario Filho, H. J.; Machado, A. J. S.; Fisk, Z. (2010-05-26). "Unconventional metallic behavior and superconductivity in the K-Mo-O system". Physical Review B. American Physical Society (APS). 81 (17): 174532. Bibcode:2010PhRvB..81q4532A. doi:10.1103/physrevb.81.174532. ISSN 1098-0121. S2CID 123147025.
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