Rietveld refinement of the coronadite structure

Rietveld refinements using X-ray powder-diffraction data of coronadite samples from Morocco (Pb (sub 1.06) Ba (sub 0.10) Mn (sub 7.7) V (sub 0.20) Al (sub 0.08) O (sub 16) ) and Australia (Pb (sub 1.40) Mn (sub 7.9) Al (sub 0.05) Zn (sub 0.05) O (sub 16) .1.55H (sub 2) O) in space group I2/m, a 9.938(2), b 2.8678(5), c 9.834(2) Angstrom, beta 90.39(2) degrees (Morocco) and a 9.913(1), b 2.8652(4), c 9.843(1) Angstrom, beta 90.20(1) degrees (Australia) confirm the basic hollandite structure. The Pb displaced approx 0.60 Angstrom along the tunnels from the special position at (0, 0, 0). This displacement increases inter-cation distances in the tunnels, allowing up to two-thirds of the tunnel sites to be occupied by Pb cations. [Authors' abstract]