Location of Cs ions in a hollandite-related superstructure

The techniques of electron diffraction, high-resolution electron microscopy, and energy dispersive analysis of X-rays are applied simultaneously to preparations of mixed (Cs,Ba)-titanates. It is shown that Cs does not substitute randomly for Ba in the hollandite-related phase Ba₂Ti₉O₂₀ but instead forms a Cs-titanate having probable stoichiometry Cs₂Ti₄O₉. For some sample preparation conditions (≦ 1200°C) lamellae of a Cs-titanate phase were observed to coherently intergrow with Ba₂Ti₉O₂₀. However, such intergrowths are probably metastable since for preparation temperatures ≧ 1350°C two distinct phases occurred, being essentially pure Ba₂Ti₉O₂₀ and Cs₂Ti₄O₉. The Cs-titanate phase appears to have structure different than previously reported, since neither single crystal electron diffraction patterns nor X-ray powder patterns could be indexed using unit cell parameters reported previously for Cs₂Ti₄O₉.