Molybdenum bronze

Short description: Generic name for certain mixed oxides of molybdenum

In chemistry, molybdenum bronze is a generic name for certain mixed oxides of molybdenum with the generic formula AxMoyOz 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.

## Contents

* 1 Preparation
* 2 Classification
* 3 Electrical and thermal properties
* 4 See also
* 5 References

## Preparation

The first report of a "molybdenum bronze" was by Alfred Stavenhagen and E. Engels in 1895. They reported that electrolysis of molten Na2MoO4 and MoO3 gave indigo-blue needles with metallic sheen, which they analysed by weight as Na2Mo5O7.[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" K0.26MoO3 and "blue" K0.28MoO3, by electrolysis of molten K2MoO4+MoO3 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 MoO2 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 Li0.9Mo6O17 and its metal-to-insulator transition at about 24 K.[5]

Hydrogen bronzes HxMoO3 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 A0.33MoO3, that is, AMo3O9:[7]
* Lithium molybdenum red bronze Li0.33MoO3 Reau and others.[7][8]
* Potassium molybdenum red bronze K0.26Mo1.02O3[3] or K0.3MoO3[8][9]
* Cesium molybdenum red bronze Cs0.33MoO3[8]
* Potassium molybdenum red bronze K0.23Mo1.01O3 a semi-conductor.[3]
* Blue bronzes, with limiting composition A0.30MoO3, that is, A3Mo10O30.[7] Their electronic properties generally do not depend on the metal A.[1]
* Potassium molybdenum blue bronze K0.28Mo1.02O3[3] or K0.3MoO3[8][9]
* Rubidium molybdenum blue bronze Rb0.3MoO3[3][9]
* Thallium molybdenum blue bronze Tl0.3MoO3[10]
* Purple bronzes, generally with limiting formula A0.9Mo6O17. Their electronic properties depend strongly on the metal A.[1]
* Lithium molybdenum purple bronze Li0.9Mo6O17
* Sodium molybdenum purple bronze Na0.9Mo6O17
* Potassium molybdenum purple bronze K0.9Mo6O17
* Rubidium molybdenum purple bronze Rb0.9Mo6O17
* Thallium molybdenum purple bronze Cs0.9Mo6O17[11]

The hydrogen molybdenum bronzes have similar appearances but different compositions:

* Hydrogen molybdenum orthorhombic blue bronze HxMoO3, 0.23 < x < 0.4 [12]
* Hydrogen molybdenum monoclinic blue bronze HxMoO3, 0.85 < x < 1.4 [12]
* Hydrogen molybdenum red bronze HxMoO3, 1.55 < x < 1.72 [12]
* Hydrogen molybdenum green bronze H2MoO3 or MoO2.H2O [6][12]

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

* Tetragonal KMo4O6[13][14]
* KxMoO2−δ.[15]

## Electrical and thermal properties

## See also

* Chemistry:Sodium tungsten bronze - Chemical intercalation compound

## References

1. ↑ 1.0 1.1 1.2 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. doi:10.1016/0022-4596(87)90231-3. ISSN 0022-4596. Bibcode: 1987JSSCh..66..163O.
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. https://zenodo.org/record/1425802.
3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 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. ↑ 4.0 4.1 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. doi:10.1016/0038-1098(84)90944-x. ISSN 0038-1098. Bibcode: 1984SSCom..51..671G.
6. ↑ 6.0 6.1 Glemser, Oskar; Lutz, Gertrud (1950). "Über ein Hydroxydhydrid des Molybdäns" (in de). Die Naturwissenschaften (Springer Science and Business Media LLC) 37 (23): 539–540. doi:10.1007/bf00589341. ISSN 0028-1042. Bibcode: 1950NW.....37..539G.
7. ↑ 7.0 7.1 7.2 7.3 7.4 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. doi:10.1006/jssc.2001.9450. ISSN 0022-4596. Bibcode: 2002JSSCh.164...81C.
8. ↑ 8.0 8.1 8.2 8.3 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. doi:10.1016/0022-4596(86)90120-9. ISSN 0022-4596. Bibcode: 1986JSSCh..64...47T.
9. ↑ 9.0 9.1 9.2 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. doi:10.1016/0038-1098(85)90863-4. ISSN 0038-1098. Bibcode: 1985SSCom..56.1023C.
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. ↑ 12.0 12.1 12.2 12.3 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. doi:10.1016/0022-4596(79)90193-2. ISSN 0022-4596. Bibcode: 1979JSSCh..29..367B.
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. doi:10.1006/jssc.1993.1008. ISSN 0022-4596. Bibcode: 1993JSSCh.102...69R.
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. doi:10.1103/physrevb.81.174532. ISSN 1098-0121. Bibcode: 2010PhRvB..81q4532A. https://www.escholarship.org/uc/item/9dr030xf.

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