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Raman spectroscopic study of azurite and malachite at 298 and 77 K

Frost, Ray L., Martens, Wayde N., Rintoul, Llew, Mahmutagic, Emir, & Kloprogge, J. Theo (2002) Raman spectroscopic study of azurite and malachite at 298 and 77 K. Journal of Raman Spectroscopy, 33(4), pp. 252-259.

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Abstract

Azurite {Cu2+3(CO3)2(OH)2} and malachite {Cu2+2(CO3)(OH)2} are both monoclinic hydroxy carbonates of copper. The Raman spectra of these two minerals have been collected at both 298 and 77 K together with the single crystal Raman spectra of azurite at 298 K. The spectra of both azurite and malachite contain modes of three separate vibrational groups: OH, CO3 and Cu-O. Accordingly, for azurite the bands at 3453 and 3427 cm-1 have been assigned as the O-H stretching mode with the O-H bending modes found at 1035 and 952 cm-1. Malachite displays two hydroxyl stretching bands at 3474 and 3404 cm-1 at 298 K which shift to 3470 and 3400 cm-1 at 77 K while O-H out-of-plane bending modes are found at 1045 and 875 cm-1. For the carbonate group, bands are observed at 1090 cm-1 (ν1), 837 and 817 cm-1 (ν2), 1490 and 1415 cm-1 (ν 3), and 769 and 747 cm-1 (ν 4). The effect of collecting the spectra at 77 K results in considerable band narrowing. The Raman spectra of the single crystals of azurite show the orientation dependence of the vibrational modes. A mechanism for ν2 splitting is proposed whereby vertical carbonate ions couple to form an in-phase and out of phase bending modes. Combination of these vibrational modes such as ν 1 + ν 3, ν 1 + ν3, ν1 + ν4 and 2ν2 are found at 2530, 2414, 1860, and 1670 cm-1, respectively. IR bands for the Cu-O stretching modes are observed at 495 and 400 cm-1, while Cu-O bending modes occur at 455 and 345 cm-1. Bands at 305 and 240 cm-1 are assigned to the O-Cu-OH bending modes. The Raman out-of-plane bending modes are found at 194 and 170 cm-1. For the carbonate group, infrared bands are observed at 1095 cm-1 (ν1), 834 and 816 cm-1(ν2), 1430 and 1419 cm-1 (ν3) and 764 and 739 cm-1 (ν 4). Combination of the CO3 vibrational modes ν1 + ν4 is observed at 1860 cm-1. IR bands for Cu-O stretching modes are observed at 580, 570 and 505 cm-1.

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ID Code: 1329
Item Type: Journal Article
DOI: 10.1002/jrs.848
ISSN: 0377-0486
Subjects: Australian and New Zealand Standard Research Classification > CHEMICAL SCIENCE (030000) > INORGANIC CHEMISTRY (030200)
Divisions: Past > QUT Faculties & Divisions > Faculty of Science and Technology
Past > Schools > School of Physical & Chemical Sciences
Copyright Owner: Copyright 2002 John Wiley & Sons
Copyright Statement: The definite version is available on publication at www3.interscience.wiley.com
Deposited On: 20 Jul 2006
Last Modified: 25 Feb 2013 13:55

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