Preparation and crystal structure of layered niobium oxides: Rb(Mg0.34Nb1.66)O5 and K(Fe0.43Nb1.57)O5

Single crystals of layered niobium oxides, Rb(Mg0.34Nb1.66)O5 and K(Fe0.43Nb1.57)O5, were prepared at 1200°C. The niobium oxides crystallized in the KTiNbO5-type structure and have the orthorhombic space group Pnma with Z = 4 and the lattice parameters are a = 6.571(1), b = 3.858(1), and c = 19.077(1) إ for Rb(Mg0.34Nb1.66)O5, and a = 6.533(1), b = 3.820(2), and c = 18.682(2) إ for K(Fe0.43Nb1.57)O5. The single-crystal structure refinements led to R = 0.032 and Rw = 0.031 for Rb(Mg0.34Nb1.66)O5 and to R = 0.049 and Rw = 0.064 for K(Fe0.43Nb1.57)O5. The niobium and iron/magnesium atoms are statistically distributed in a unit of doubled octahedra sharing edges. Alkaline ions in the interlayer were ion exchanged with protons to yield hydrated protonated compounds, H(M,Nb)2O5·nH2O (M = Mg,Fe).