Chemical and structural evolution of alkali titanate oxides A2TinO2n+1 (2 ≤ n ≤ 6)

Alkali titanate oxides with the general formula A₂Ti_nO_2n+1 (where A is an alkali element) have been the subject of extensive research for energy storage applications, due to their remarkable electrical and electrochemical properties, particularly when hydrated.

Initially, we focused on the A₂Ti_nO₅ family (with A = K or Rb), as these compounds are promising candidates as solid electrolytes for supercapacitors [1]. Indeed, they exhibit very high dielectric constants at low frequencies as well as particularly encouraging ionic conductivities, on the order of 10^-3 S·cm^-1 for Rb₂Ti₂O₅, for example [2, 3]. These properties vary significantly depending on the hydration level, with a marked difference between hydrated and dehydrated materials; the latter showing much lower conductivities [3], highlighting the central role of water in ionic conduction mechanisms. In this context, this research aims to gain a better understanding of these conduction mechanisms. To this end, we investigated the structural and physicochemical evolution of these materials in the presence of water and CO₂ [4]. We thereby highlight a degradation mechanism linked to a carbonation process, studied using a multi-technique experimental approach including X-ray and neutron diffraction, thermogravimetric analysis (TGA), and infrared (IR) spectroscopy.

In this presentation, I will present the results obtained from our study on A₂Ti₂O₅ compounds. We will then establish the relationship between crystal structure and stability by extending the degradation study to A₂Ti₄O₉ and A₂Ti₆O₁₃ compounds under ambient conditions. More specifically, we show that there is a direct correlation between structural degradation and crystallographic features related to the coordination environment of titanium. These results enable a deeper understanding of the most appropriate conditions for the application of these materials in the field of energy applications.

[1] Federicci, R.; Hole, S.; Demery, V.; Leridon, B. J. Appl. Phys. 2018, 124 (15), 152104.

[2] Federicci, R.; Hole, S.; Popa, A. F.; Brohan, L.; Baptiste, B.; Mercone, S.; Leridon, B.. Phys. Rev. Mater. 2017, 1 (3), 032001.

[3] de Sousa Coutinho, S.; Bérardan, D.; Lang, G.; Federicci, R.; Giura, P.; Beneut, K.; Dragoe, N.; Holé, S.; Leridon, B. Solid State Ionics 2021, 364, 115630.

[4] Meziani, N.; Parent, M.; Rousse, G.; Leridon, B.; Berardan, D.; Giura, P. Inorg. Chem. 2024, 63 (38), 17513–17524.