Maximized cation size disorder driven phonon engineering in high-entropy pyrochlores of La2(Zr,Ce,Hf,Sn,Ti)2O7

Abstract

It is crucial to develop low thermal conductivity(k) materials for thermal barrier coatings of next-generation aero-engines. Through a size disorder oriented approach, novel B-site non-equalmolar high-entropy pyrochlores of La₂(Zr,Ce,Hf,Sn,Ti)₂O₇ have been designed and successfully synthesized, which exhibits a combination of desirable thermophysical properties, i.e. thermal conductivities reaching 1.46 W·m^-1·K^-1, approximately 33% lower than those of La₂Zr₂O₇. The phonon scattering prediction and fitting model under point defect influence along with thermal radiation effects were systematically investigated, elucidating the phonon scattering mechanisms and the critical roles of cation size disorder (δ_B) in thermal conductivity reduction. Furthermore, an improved model has been developed to accurately depict the full-temperature-range thermal conductivity, revealing the detailed thermal transport processes and characteristics in the high-entropy ceramic La₂(Zr,Ce,Hf,Sn,Ti)₂O₇ across the entire temperature range.