Selection of low and ultra-low thermal conductivity materials for insulating layers of TBC systems in the context of computational materials science opportunities—a review

This article concerns the direction of development of ceramic materials with ultra-low thermal conductivity and minimum thermal conductivity as the basis for selection as insulating layers of thermal barrier coatings (TBC). Firstly, information on the requirements for ceramic materials dedicated to TBCs was reviewed, and the influence of fundamental factors on phonon scattering mechanisms was described. The role of oxygen vacancies and doped atoms of different masses and cation radii was determined. The second part reviews the most frequently researched materials for TBC systems. Zirconia-based compounds modified with yttrium, hafnium, cerium oxides, rare earth oxides, and other groups of materials, including high-entropy materials, are described. The minimum thermal conductivity value was used as the primary parameter characterizing these materials. The next part of the article presents the results of calculations of this parameter based on data from density functional theory (DFT) simulations, machine learning (ML) procedures, and the descriptor method. The last part presents the diffusivity/thermal conductivity experiment results for selected zirconates (using a laser flash (LFA) method). On their basis, the minimum value of thermal conductivity was estimated, which corresponded to the range of the so-called glass-like thermal conductivity. The obtained experimental results were compared with the calculated data.