EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Multicomponent equiatomic oxides (MEOs), also named high entropy oxides (HEOs), have attracted great interest in recent years. Analogous to high entropy alloys (HEAs), they consist of five or more different cations on one or more cation sublattice in approximately same amount. , This leads to a big variety of compositions with adjustable material properties and promising versatile characteristics like reversible lithium storage, ionic conductivity, catalytic activity and dielectric and magnetic properties. The high configurational entropy obtained by equimolar mixing of the cations results in improved phase stability at high temperatures according to the Gibbs-Helmholtz equation and low thermal conductivity due to increased phonon scattering caused by different cation size, mass and valency state. Therefore, MEOs are proposed as promising materials for future thermal barrier coatings (TBCs). However, development of new TBC materials requires a systematic examination of promising candidates, from synthesis to thermophysical and thermochemical characterization and investigation of mechanical properties.

In this work, multicomponent pyrochlore oxides with the general formula A2Zr2O7 and 5 different cations on the A-site have been synthesized. The composition has been varied systematically regarding ion size and valency to evaluate its influence on crystal structure, phase stability and material properties. For A, transition metals such as La, Nd, Sm, Gd, Y and Zr were used. Samples have been synthesized using reverse co precipitation and solid-state sintering. The chemical and structural characterization was performed using X-ray diffraction, scanning electron microscopy, Raman spectroscopy and electron microprobe. Thermal analysis and long-term annealing experiments were conducted to assess the thermal stability as well as thermodynamic and thermophysical characterization of the compounds. The results of this work represent the foundation for the development of novel MEO-based TBCs.