Exploring fundamental aspects of the structural organization in weberite-type tantalate oxides
Résumé
The design of advanced energy-related materials that are specifically engineered to maintain structural stability in a variety of harsh operating conditions, such as high pressure, temperature, and radiation fields, requires the development of specific experimental techniques and analyses that address the organization of complex materials over length scales that range from the interatomic distances to several hundreds of nanometers. Such structural characterization is important as compositional and structural disorder forms as a consequence of exposure to extremes that impact thermal, mechanical, and chemical properties. Weberite-type tantalate oxides (A3TaO7) are promising candidates for many energy-related applications, but there is only a limited understanding of how their atomic-scale structure changes as a result of exposure to extremes (e.g., high temperature and ion irradiation). We performed state-of-the-art neutron total scattering experiments across a compositional range of weberite-type tantalate oxides and analyzed the real space, short-range pair correlation functions to establish evidence that their local atomic arrangements adopt an organization different from their well-known ‘average’ structure across longer length scales. This finding appears to be a general phenomenon for a range of weberite-type oxides structures, spanning from fully ordered (orthorhombic Pr3TaO7) to fully disordered (cubic Yb3TaO7). Comparing short- and long-range structural behaviors across the compositional series have revealed a complex organization of structural correlations across different length scales: the short-range analysis suggests a strong dependence on the ionic radius of the A-site cation and the distortion of a local structural motif that monotonically increases across the compositional series, while the long-range analysis confirmed the existence of three distinct structure types. This behavior is explained by the incompatibility of tilt systems in the long-range structure due to the increasing local distortions.
Acknowledgment: This work was supported in part by the French Grant ANR-10-LABX-0039-PALM and by the Joint Ph.D. Programme of Université Paris-Saclay as part of the « Investissements d’Avenir » program grant number ANR-11-IDEX-0003.