Identifying characteristics of the fibrous cesium titanate Cs₂Ti₅O₁₁

Electron microscopic studies of the fibrous cesium titanate Cs₂Ti₅O₁₁ reveal characteristic features not readily apparent using standard methods of phase analysis (optical microscopy, X-ray diffraction). Its fibrous needle-like laths give characteristic diffuse scattering, complicating the indexing of electron diffraction patterns. The hydrated form Cs₂Ti₅O₁₁ · (1 + x)H₂O (0.5 < x < 1) is typically grossly distorted, resembling pyrolytic graphite. Cs₂Ti₅O₁₁ is unstable when stored under ambient conditions at room temperature for ∼1 year when disproportionation into Cs₂Ti₄O₉ and Cs₂Ti₆O₁₁ · nH₂O occurs. The structure of Cs₂Ti₅O₁₁ and intergrowth defects in the unstable forms have been studied by high-resolution electron microscopy. It is evident that these phases would be undesirable in titanate ceramics such as SYNROC, which are designed for immobilization of radioactive ¹³⁷C_s.