X-ray Photoelectron spectroscopic and Raman spectroscopic study of bayldonite from Wheal Carpenter, Cornwall, UK

Abstract

Bayldonite [Cu3Pb(AsO4)2(OH)2], Wheal Carpenter (Cornwall, UK) was studied by X-ray Photoelectron Spectroscopy and Raman Microscopy. X-ray Photoelectron Spectroscopy revealed single copper, lead and arsenic positions in the crystal structure. Two oxygen bands with a 1:4 ratio were associated oxygen positions in arsenate- and hydroxyl-groups, excluding the presence of acidic arsenate groups. The relatively large difference in binding energy for the two oxygen bands was interpreted as being due to the dynamic Jahn-Teller distortion of the copper octahedral in the bayldonite crystal structure. Raman microscopy showed bands at 804 and 837 cm−1 assigned to arsenate antisymmetric stretching mode and the symmetric stretching mode. Supported by the X-ray Photoelectron Spectroscopic results the bands at 726, 761, 822 and 886 cm−1 were assigned to copper-hydroxyl modes. Bands around 497 cm−1 were assigned to the arsenate antisymmetric bending modes and around 427 cm−1 to the symmetric bending modes. The 539 cm−1 band was associated with a copper-hydroxyl stretching mode or another υ4. The region 250–400 cm−1 showed sharp bands at 313 and 328 cm−1 with weaker bands at 298 and 342 cm−1 assigned to copper-oxygen and/or lead-oxygen stretching modes.