Molybdenum bronze explained

In chemistry, molybdenum bronze is a generic name for certain mixed oxides of molybdenum with the generic formula 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. The oxidation states in K_0.28MoO₃ 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 and gave indigo-blue needles with metallic sheen, which they analysed by weight as . The first unambiguous synthesis of alkali molybdenum bronzes was reported only in 1964, by Wold and others. They obtained two potassium bronzes, "red" and "blue", by electrolysis of molten + 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 is obtained.

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 and its metal-to-insulator transition at about 24 K.

Hydrogen bronzes were obtained in 1950 by Glemser and Lutz, by ambient-temperature reactions. 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.

Classification

Molybdenum bronzes are classified in three major families:

• Red bronzes with limiting composition, that is, :
  • Lithium molybdenum red bronze Reau and others.
  • Potassium molybdenum red bronze or
    • • Cesium molybdenum red bronze Potassium molybdenum red bronze a semi-conductor.
• Blue bronzes, with limiting composition, that is, . Their electronic properties generally do not depend on the metal A.
  • Potassium molybdenum blue bronze or
    • • • Rubidium molybdenum blue bronze Thallium molybdenum blue bronze Purple bronzes, generally with limiting formula . Their electronic properties depend strongly on the metal A.

The hydrogen molybdenum bronzes have similar appearances but different compositions:

• Hydrogen molybdenum orthorhombic blue bronze, 0.23 < x < 0.4
• Hydrogen molybdenum monoclinic blue bronze, 0.85 < x < 1.4
• Hydrogen molybdenum red bronze, 1.55 < x < 1.72
• Hydrogen molybdenum green bronze or .

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

• • Tetragonal .

References

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Notes and References

1. Glemser . Oskar . Lutz . Gertrud . Über ein Hydroxydhydrid des Molybdäns . Die Naturwissenschaften . Springer Science and Business Media LLC . 37 . 23 . 1950 . 0028-1042 . 10.1007/bf00589341 . 539–540 . 1950NW.....37..539G . 46699509 . de.
2. 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.
3. Collins . B.T. . Ramanujachary . K.V. . Greenblatt . M. . Waszczak . J.V. . Charge-density wave instability and nonlinear transport in Tl_0.3MoO₃ a new blue molybdenum oxide bronze . Solid State Communications . Elsevier BV . 56 . 12 . 1985 . 0038-1098 . 10.1016/0038-1098(85)90863-4 . 1023–1028. 1985SSCom..56.1023C .
4. Wold . A. . Kunnmann . W. . Arnott . R. J. . Ferretti . A. . Preparation and Properties of Sodium and Potassium Molybdenum Bronze Crystals . Inorganic Chemistry . American Chemical Society (ACS) . 3 . 4 . 1964 . 0020-1669 . 10.1021/ic50014a022 . 545–547.
5. Andrade . Margareth . Maffei . Mariana Lanzoni . Alves . Leandro Marcos Salgado . Santos . Carlos Alberto Moreira dos . Ferreira . Bento . Sartori . Antonio Fernando . Microstructure and metal-insulator transition in single crystalline KMo₄O₆ . Materials Research . FapUNIFESP (SciELO) . 15 . 6 . 2012-10-11 . 1980-5373 . 10.1590/s1516-14392012005000132 . 998–1002. free .
6. 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. . Unconventional metallic behavior and superconductivity in the K-Mo-O system . Physical Review B . American Physical Society (APS) . 81 . 17 . 2010-05-26 . 1098-0121 . 10.1103/physrevb.81.174532 . 174532. 2010PhRvB..81q4532A . 123147025 .
7. Ramanujachary . K.V. . Greenblatt . D.M. . Jones . E.B. . McCarroll . W.H. . Synthesis and Characterization of a New Modification of the Quasi-Low-Dimensional Compound KMo₄O₆ . Journal of Solid State Chemistry . Elsevier BV . 102 . 1 . 1993 . 0022-4596 . 10.1006/jssc.1993.1008 . 69–78. 1993JSSCh.102...69R .
8. Greenblatt . M. . McCarroll . W.H. . Neifeld . R. . Croft . M. . Waszczak . J.V. . Quasi two-dimensional electronic properties of the lithium molybdenum bronze, Li_0.9Mo₆O₁₇ . Solid State Communications . Elsevier BV . 51 . 9 . 1984 . 0038-1098 . 10.1016/0038-1098(84)90944-x . 671–674. 1984SSCom..51..671G .
9. Onoda . M. . Toriumi . K. . Matsuda . Y. . Sato . M. . Crystal structure of lithium molybdenum purple bronze Li_0.9Mo₆O₁₇ . Journal of Solid State Chemistry . Elsevier BV . 66 . 1 . 1987 . 0022-4596 . 10.1016/0022-4596(87)90231-3 . 163–170. 1987JSSCh..66..163O .
10. Chin . Kin . Eda . Kazuo . Sotani . Noriyuki . Whittingham . M.Stanley . Hydrothermal Synthesis of the Blue Potassium Molybdenum Bronze, K_0.28MoO₃ . Journal of Solid State Chemistry . Elsevier BV . 164 . 1 . 2002 . 0022-4596 . 10.1006/jssc.2001.9450 . 81–87. 2002JSSCh.164...81C .
11. Tsai . P.P. . Potenza . J.A. . Greenblatt . M. . Schugar . H.J. . Crystal structure of Li_0.33MoO₃, a stoichiometric, triclinic, lithium molybdenum bronze . Journal of Solid State Chemistry . Elsevier BV . 64 . 1 . 1986 . 0022-4596 . 10.1016/0022-4596(86)90120-9 . 47–56. 1986JSSCh..64...47T .
12. 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.
13. Stavenhagen . A. . Engels . E. . Ueber Molybdänbronzen . Berichte der Deutschen Chemischen Gesellschaft . Wiley . 28 . 2 . 1895 . 0365-9496 . 10.1002/cber.189502802213 . 2280–2281.
14. Birtill . J.J. . Dickens . P.G. . Thermochemistry of hydrogen molybdenum bronze phases H_xMoO₃ . Journal of Solid State Chemistry . Elsevier BV . 29 . 3 . 1979 . 0022-4596 . 10.1016/0022-4596(79)90193-2 . 367–372. 1979JSSCh..29..367B .
15. Whangbo . M. H. . Schneemeyer . L. F. . Band electronic structure of the molybdenum blue bronze A_0.30MoO₃ (A = K, Rb) . Inorganic Chemistry . American Chemical Society (ACS) . 25 . 14 . 1986 . 0020-1669 . 10.1021/ic00234a028 . 2424–2429.