Acta Crystallographica Section B

Structural Science

Volume 64, Part 1 (February 2008)

research papers

Acta Cryst. (2008). B64, 34-41 [ doi:10.1107/S0108768107066402 ]

Crystal chemistry of mimetite, Pb₁₀(AsO₄)₆Cl_1.48O_0.26, and finnemanite, Pb₁₀(AsO₃)₆Cl₂

T. Baikie, C. Ferraris, W. T. Klooster, S. Madhavi, S. S. Pramana, A. Pring, G. Schmidt and T. J. White

Abstract: The crystal chemistries of synthetic mimetite, Pb₁₀(As⁵⁺O₄)₆(Cl_2 - xO_x/2), a neutral apatite, and finnemanite, Pb₁₀(As³⁺O₃)₆Cl₂, a reduced apatite, were characterized using a combination of X-ray powder diffraction, neutron diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. Both phases conform to hexagonal P6₃/m symmetry; however, the temperature-driven transformation of clinomimetite to mimetite described earlier was not confirmed. The average mimetite structure is best described through the introduction of partially occupied oxygen sites. A better understanding of the mixed arsenic speciation in apatites can guide the formulation of waste form ceramics and improve models of long-term durability after landfill disposal.

Keywords: powder diffraction; transmission electron microscropy; photoelectron spectroscopy; ceramics.