Thermophysical Property Tuning in Compositionally Complex Rare Earth Titanate and Zirconate Families

In multicomponent ceramics there are a variety of factors that determine phase selection and stability such as the configurational entropy of the system, the ionic radii of the constituent cations, and the propensity for vacancies, anti-site defects, and other types of crystalline disorder. The influence of these factors varies with the structural and chemical complexity of the crystal system, potentially giving rise to an expanded degree of physical property tuning in compositionally complex variants. We explore structure-property trends in two compositionally complex oxide families, titanate pyrochlores (RE₂Ti₂O₇) and zirconate fluorites (RE_0.5Zr_0.5O_2-x), taking advantage of the large diversity of ionic radii available in the Lanthanide series (RE=La to Lu, large to small). We present thermal conductivity and thermal expansion coefficient trends across the series, and we examine corresponding average and local atomic structures using X-ray and neutron diffraction and pair distribution function analysis. Various mechanochemistry and sintering pathways are shown to influence cation chemical short-range order and grain size control in compositions with promising property combinations. Structural stability is examined at extreme temperatures (~2800 °C) using aerodynamic levitation and laser heating, evaluating their suitability as potential next generation thermal barrier coatings. Determining the impact of high entropy configurations on pyrochlore and fluorite stability windows, defect formation, and other crystal-chemical factors, provides deeper understanding of possible design considerations for intrinsic property enhancement in these and other multicomponent complex ceramics.