A family
of rubidium-containing mixed-metal titanates, Rb
x
M
y
Ti8‑y
O16 (M = Mg, Mn, Fe, Ni, and Cu) was prepared
as high-quality single crystals employing a molten RbCl-RbF flux at
850 °C. This is the first report of rubidium-based mixed-metal
titanium hollandite materials grown as single crystals. All compounds
crystallize in the tetragonal space group I4/m in the hollandite structure type featuring a three-dimensional
framework, composed of mixed Ti/M octahedra, containing square, 2
× 2 tunnels occupied by the Rb cations. Herein, we report on
the molten salt-flux crystal growth and solid state synthesis of the
phases, the structures of the flux grown crystals, and the magnetic
and optical properties of these materials. Magnetization versus temperature
measurements for the Fe, Ni, and Cu analogues indicate that all compositions
are Curie paramagnets with effective magnetic moments consistent with
their respective d-electron count. First-principles calculations in
the form of density functional theory were performed to calculate
the relative stability, adsorption indexes, and the density of states
for select compositions, all of which exhibit stability at 0 K with
the computed optical band gaps consistent with the observations.