Manganese doping in bismuth aluminate

GRANONE L. I.; CURTI M.; GESING TH. M.; MURSHED M.M.; BREDOW T.; MENDIVE C.

Mar del Plata

Congreso; X Reunión de la Asociación Argentina de Cristalografía; 2014

Asociación Argentina de Cristalografía

Mullite-typeO9-compounds with general formula Bi2M4O9 (Figure1) are very interesting materials due to the capability of functioning as photocatalysts upon absorption of visible light. The main motifs of these structures are one-dimensional chains of edge sharing MO6 octahedra, M2O7 double tetrahedral units and BiO6E groups, where E refers to a 6s2 lone electron pair (LEP) interconnecting the octahedral chains along the c-axis [1]. When Bi2Al4O9 is doped with an increasing amount of manganese in some M-sites the optical bandgap shifts thus impacting in the photocatalytic properties of the different doped compounds. The role of the LEPs and the consequent structural changes with different concentrations of transition metals atoms in the lattice are of key importance for the understanding of the photocatalytic properties.Experimental results based on measurements of the unit cell volume showed that aluminum by manganese substitution in Bi2Al4O9 reaches a maximum saturation level. In that case, a final formula Bi2(Al(1-x)Mnx)4O9 with x ≈ 0.25 was obtained. Interestingly, atomic substitutions of manganese by aluminium in the end-member Bi2Mn4O10, a mullite-type O10-compound, are not possible.Theoretical calculations of the doped compounds were done and compared to the respective experimental results, thus complementing the characterization of structural parameters. Periodic calculations for geometry optimizations at all possible doping levels were performed with the crystalline orbital program CRYSTAL09 [2] employing the Hartree Fock-Density Functional Theory (HF-DFT) hybrid method: PW1PW [3].The number and the corresponding volume of both tetrahedral and octahedral sites within the different crystalline compounds were placed in focus in the discussion for the role of the LEPs as a key parameter in the doped structures.[1] R. X. Fischer, H. Schneider, The Mullite-Type Family of Crystal Structures, ed. H. Schneider and S.Komarneni, Mullite Wiley-VCH Weinheim, 2005, vol. 1?46, 128?140. [2] R. Dovesi, V. R. Saunders, C. Roetti, R. Orlando, C. M. Zicovich-Wilson, F.Pascale, B. Civalleri, K. Doll, N. M. Harrison, I. J. Bush, P. DArco and M. Llunell, CRYSTAL09, 2009, CRYSTAL09 User´s Manual. University of Torino, Torino.[3] T. Bredow, A. R. Gerson, Phys. Rev. B,61, 2000, 5194?5201.