Synthesis and crystal structure of novel hollandite compounds A(x)Mg(x)/2Sn(8-x/2)O(16) (A = K, Rb, and Cs)

We have prepared novel hollandite compounds A(x)Mg(x)/2Sn8-x/2O16 (A = K, R b, and Cs) by solid state reaction, using A(2)CO(3) (A = K, Rb, and Cs), Mg (NO3)(2). 6H(2)O and SnO2 in the molar ratio 1 : 1 : 3, at 1500 degrees C f or 5 hours in air. All compounds crystallize in the monoclinic space group C2/m. Their crystal structures and compositions were determined by the Riet veld analysis using X-ray powder diffraction data. K2MgSn7O16: a = 14.837(3 ) Angstrom, b = 3.1667(1) Angstrom, c = 10.490(2) Angstrom, beta = 134.919( 8) Angstrom, and Z = 1, R-I = 7.32%. Rb2MgSn7O16: a = 14.890(4) Angstrom, b = 3.1706(1) Angstrom, c = 10.514(3) Angstrom, beta = 134.989(13) Angstrom, and Z = 1, R-B = 8.97%. Cs1.26Mg0.63Sn7.37O16: a = 15.015(3) Angstrom, b = 3.1656(1) Angstrom, c = 10.621(3) Angstrom, beta = 135.061(11) Angstrom, a nd Z = 1, R-I = 9.24%. Sn and Mg octahedra form the hollandite framework, a nd alkali ions are located in the hollandite tunnels. The Cs ion only parti ally occupies the tunnel, because the length of b-axis is shorter than Cs i on size. As a result, Cs hollandite only has the non-stoichiometric composi tion.