Structure of two new borates YCa3(A1O)3(BO3)4 and YCa3(GaO)3(BO3)4

By replacing Mn in YCa3(MnO)(3)(BO3)(4) with trivalent Al and Ga, two new borates with the compositions of YCa3(MO)(3)(BO3)(4) (M = Al, Ga) were prepared by solid-state reaction. Structure refinements from X-ray powder diffraction data revealed that both of them are isostructural to gaudefroyite with a hexagonal space group P6(3)/m. Cell parameters of a = 10.38775(13)angstrom, c = 5.69198(10)angstrom for the Al-containing compound and a = 10.5167(3)angstrom, c = 5.8146(2)angstrom for the Ga analog were obtained from the refinements. The structure is constituted of AlO6 or GaO6 octahedral chains interconnected by BO3 groups in the ab plane to form a Kagome-type lattice, leaving trigonal and apatite-like tunnels. It is found that most rare-earth and Cr, Mn ions can be substituted into the Y3+ and M3+ sites, respectively, and the preference of rare-earth ions to locate in the trigonal tunnel is correlated to the sizes of the M3+ ions. (C) 2005 Elsevier Inc. All rights reserved.