Phase formation capability and compositional design of β-phase multiple rare-earth principal component disilicates.

A key strategy to design environmental barrier coatings focuses on doping multiple rare-earth principal components into β-type rare-earth disilicates (RE 2 Si 2 O 7 ) to achieve versatile property optimization. However, controlling the phase formation capability of (nRE xi ) 2 Si 2 O 7 remains a crucial challenge, due to the complex polymorphic phase competitions and evolutions led by different RE 3+ combination. Herein, by fabricating twenty-one model (RE I 0.25 RE II 0.25 RE III 0.25 RE IV 0.25 ) 2 Si 2 O 7 compounds, we find that their formation capability can be evaluated by the ability to accommodate configurational randomness of multiple RE 3+ cations in β-type lattice while preventing the β-to-γ polymorphic transformation. The phase formation and stabilization are controlled by the average RE 3+ radius and the deviations of different RE 3+ combinations. Subsequently, based on high-throughput density-functional-theory calculations, we propose that the configurational entropy of mixing is a reliable descriptor to predict the phase formation of β-type (nRE xi ) 2 Si 2 O 7 . The results may accelerate the design of (nRE xi ) 2 Si 2 O 7 materials with tailored compositions and controlled polymorphic phases.