Active learning driven materials discovery for low thermal conductivity rare-earth pyrochlore for thermal barrier coatings

High-Entropy/multicomponent rare-earth oxides (HECs and MCCs) show promise as alternative materials for thermal barrier coatings (TBC) with the ability to tailor properties based on the combination of rare-earth elements present. By enabling the substitution of scarce or supply-risk rare-earths with more readily available alternatives while maintaining comparable material performance, HECs and MCCs offer a valuable path towards alternative TBC material design. However, navigating this search space of compositionally complex materials is both time and resource intensive. In this study, an active learning (AL) framework was employed to identify HEC/MCC materials with a pyrochlore structure, with acceptable thermal conductivity (TC) for TBC applications. The AL framework was applied through a Bayesian optimisation (BO) strategy, coupled with a random forest surrogate model. TC was selected as the optimisation criterion as that is the most fundamental requirement of TBC materials. Over two iterations of the AL cycle, four compositions were generated and synthesised in the lab for experimental evaluation. The first iteration yielded two single-phase pyrochlores, ( La 0 . 29 Nd 0 . 36 Gd 0 . 36 ) 2 Zr 2 O 7 and ( La 0 . 333 Nd 0 . 26 Gd 0 . 15 Ho 0 . 15 Yb 0 . 111 ) 2 Zr 2 O 7 , with measured thermal conductivities of 2.03 and 1.90 W/mK, respectively. The surrogate model predicted a TC of 2.009 W/mK for both compositions, demonstrating its accuracy for completely new compositions. The second iteration compositions showed dual-phase when synthesised, highlighting the need to take into account phase formation in the AL framework.