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

Area of Science:

• Materials Science
• Ceramics
• Coatings Technology

Background:

• Environmental barrier coatings (EBCs) are crucial for protecting materials in high-temperature applications.
• Rare-earth disilicates (RE2Si2O7) are promising EBC candidates, but optimizing their properties through doping with multiple rare-earth elements (RE) is challenging.
• Controlling the phase formation of complex (nRExi)2Si2O7 compositions is vital for predictable performance.

Purpose of the Study:

• To investigate the factors controlling phase formation in multi-rare-earth doped β-type rare-earth disilicates.
• To identify reliable descriptors for predicting the formation of desired β-type phases in (nRExi)2Si2O7 systems.
• To provide a foundation for accelerated design of EBCs with tailored compositions and controlled polymorphic phases.

Main Methods:

• Fabrication and characterization of twenty-one model (RE^I_0.25RE^II_0.25RE^III_0.25RE^IV_0.25)2Si2O7 compounds.
• Analysis of phase formation capability based on the accommodation of configurational randomness and prevention of polymorphic transformation.
• High-throughput density-functional-theory (DFT) calculations to evaluate configurational entropy of mixing as a predictive descriptor.

Main Results:

• The formation capability of (nRExi)2Si2O7 is linked to the lattice's ability to accommodate configurational randomness of multiple RE3+ cations while avoiding the β-to-γ transformation.
• Phase formation and stabilization are governed by the average RE3+ radius and the specific combinations of RE3+ ions.
• Configurational entropy of mixing emerged as a reliable descriptor for predicting the formation of β-type (nRExi)2Si2O7 phases.

Conclusions:

• The study establishes a framework for understanding and controlling phase formation in complex rare-earth disilicates.
• Configurational entropy of mixing is proposed as a key predictive tool for designing novel EBC materials.
• These findings can accelerate the development of advanced environmental barrier coatings with optimized properties.