Raman spectroscopic study of the tellurite minerals: graemite CuTeO3·H2O and teineite CuTeO3·2H2O

Tellurites may be subdivided according to formula and structure. There are five groups based upon the formulae (a) A(XO₃), (b) A(XO₃)·xH₂O, (c) A₂(XO₃)₃·xH₂O, (d) A₂(X₂O₅) and (e) A(X₃O₈). Raman spectroscopy has been used to study the tellurite minerals teineite and graemite; both contain water as an essential element of their stability. The tellurite ion should show a maximum of six bands. The free tellurite ion will have C_3v symmetry and four modes, 2A₁ and 2 E. Raman bands for teineite at 739 and 778 cm^?1 and for graemite at 768 and 793 cm^?1 are assigned to the ν₁ (TeO₃)^2? symmetric stretching mode while bands at 667 and 701 cm^?1 for teineite and 676 and 708 cm^?1 for graemite are attributed to the ν₃ (TeO₃)^2? antisymmetric stretching mode. The intense Raman band at 509 cm^?1 for both teineite and graemite is assigned to the water librational mode. Raman bands for teineite at 318 and 347 cm^?1 are assigned to the (TeO₃)^2?ν₂(A₁) bending mode and the two bands for teineite at 384 and 458 cm^?1 may be assigned to the (TeO₃)^2?ν₄(E) bending mode. Prominent Raman bands, observed at 2286, 2854, 3040 and 3495 cm^?1, are attributed to OH stretching vibrations. The values for these OH stretching vibrations provide hydrogen bond distances of 2.550(6) Å (2341 cm^?1), 2.610(3) Å (2796 cm^?1) and 2.623(2) Å (2870 cm^?1) which are comparatively short for secondary minerals. Copyright © 2008 John Wiley & Sons, Ltd.