Chemical and Structural Evolution of Rb 2-2 x K 2 x Ti 2 O 5 Layered Titanates When Exposed to Ambient Air.

In this report, we combine thermogravimetric analysis, X-ray diffraction, and infrared spectroscopy to investigate the chemical and structural evolution upon exposure of alkali titanates Rb 2 Ti 2 O 5 and K 2 Ti 2 O 5 and mixed compound Rb 2-2 x K 2 x Ti 2 O 5 , for which 0 ≤ x ≤ 1, to the ambient atmosphere. We show that a complete solid solution exists between the potassium and rubidium end-members and that mixed compounds exhibit an intermediate behavior. When exposed to the ambient atmosphere, all compounds degrade, with the progressive formation of first hydrates and then bicarbonates and a much quicker degradation of the rubidium titanate than of the potassium titanate. On the contrary, we show that upon hydration in the absence of CO 2 , the crystal structure of K 2 Ti 2 O 5 is more quickly impacted than that of Rb 2 Ti 2 O 5 . These observations should be useful for understanding the evolution of the functional properties of M 2 Ti 2 O 5 alkali titanates upon aging in the ambient atmosphere, as well as for the optimization of their hydration-dependent properties.