Synthesis, structure, and photocatalysis in a new structural variant of the aurivillius phase: LiBi₄M₃O₁₄ (M = Nb, Ta)

Abstract

Two new compounds, LiBi₄Nb₃O₁₄ and LiBi₄Ta₃O₁₄, have been synthesized by the solid-state method, using Li₂CO₃, Bi₂O₃, and M₂O₅ (M = Nb, Ta) in stoichiometric quantities. These compounds crystallize in the monoclinic C2/c space group with a = 13.035(3) Å, b = 7.647(2) Å, c = 12.217(3) Å, β = 101.512(4)°, V = 1193.4(5) ų , and Z = 4 and a = 13.016(2) Å, b = 7.583(1) Å, c = 12.226(2) Å, β = 101.477(3)°, V = 1182.6(5) ų, and Z = 4, respectively. These are isostructural and the structure along the b axis consists of layers of [Bi₂O₂]²⁺ units separated by layers of LiO₄ tetrahedra and NbO₆ octahedra hence depicting an unusual variation in the Aurivillius phase isolated for the first time. The presence of lithium has been confirmed by ⁷Li NMR studies. ac impedance measurements and variable temperature ⁷Li NMR studies indicate oxygen ion conductivity in these materials. The UV-visible spectra suggest a band gap of 3.0 eV for LiBi₄Nb₃O₁₄ and 3.5 eV for LiBi₄Ta₃O₁₄, respectively, and the associated studies on degradation of dyes and phenols render these materials suitable for photocatalysis.