title: A vibrational spectroscopic study of the phosphate mineral Wardite NaAl₃(PO₄)₂(OH)₄·2(H₂O).
abstract: Three wardite mineral samples from different origins have been analysed by vibrational spectroscopy. The mineral is unusual in that it belongs to a unique symmetry class, namely the tetragonal-trapezohedral group. The structure of wardite contains layers of corner-linked OH bridged MO(6) octahedra stacked along the tetragonal C-axis in a four-layer sequence and linked by PO(4) groups. Consequentially not all phosphate units are identical. Thus, two intense Raman bands observed at 995 and 1051 cm(-1) are assigned to the ν(1) PO(4)(3-) symmetric stretching mode. Intense Raman bands are observed at 605 and 618 cm(-1) with shoulders at 578 and 589 cm(-1) are assigned to the ν(4) out of plane bending modes of the PO(4)(3-). The observation of multiple bands supports the concept of non-equivalent phosphate units in the structure. Sharp infrared bands are observed at 3544 and 3611 cm(-1) are attributed to the OH stretching vibrations of the hydroxyl units. Vibrational spectroscopy enables subtle details of the molecular structure of wardite to be determined.
authors.affiliation: School of Chemistry, Physics and Mechanical Engineering, Science and Engineering Faculty, Queensland University of Technology, GPO Box 2434, Brisbane, Queensland 4001, Australia. r.frost@qut.edu.au
authors.forename: Ray L
authors.initials: RL
authors.lastname: Frost
authors.forename: Yunfei
authors.initials: Y
authors.lastname: Xi
mesh_terms: D017665:Hydroxyl Radical / Q000737:chemistry; D008903:Minerals / Q000737:chemistry*; D010710:Phosphates / Q000737:chemistry*; D013055:Spectrophotometry, Infrared; D013059:Spectrum Analysis, Raman
chemical_list: D008903:Minerals; D010710:Phosphates; D017665:Hydroxyl Radical