Entropy-Inspired Materials Design for Novel Electronic Materials: A₆B₂O₁₇-Form (A = Zr, Hf; B = Nb, Ta) Oxides

In this work, we apply an entropy-inspired materials design approach to study the class of compositionally complex, disordered <i>A</i>₆<i>B</i>₂O₁₇ (<i>A</i> = Zr, Hf; <i>B</i> = Nb, Ta) family of phases. The availability of multiple local coordination sites on the cation sublattice coupled with substantial tolerance for extended chemical solubility makes this a unique system for studying the interplay between configurational entropy (controlled across multiple structural hierarchies) and properties. This work focuses on both the thermodynamic consequences of configurational entropy on phase stability as well as property characterization, with particular focus on dielectric and candidate ferroelectric behavior. This work spans studies in both the bulk and thin film regimes. First, we confirm the stability of ternary and quinary <i>A</i>₆<i>B</i>₂O₁₇ phases at high temperatures as well as substantial inherent cation sublattice disorder; moreover, we observe enhanced solid solubility in multi-constituent systems commonly associated with high-entropy material behavior. We develop a sintering procedure for producing dense ternary <i>A</i>₆<i>B</i>₂O₁₇ phases for use as both sputtering targets for thin film preparation and bulk dielectric measurements. Furthermore, we characterize the effect of sputter deposition conditions (i.e. O₂ partial pressure and total pressure) on film quality (crystallinity, roughness, and density); we also relate these parameters to observed dielectric performance. Collectively, this study leverages a range of advanced characterization techniques, including both <i>ex situ</i> and <i>in situ</i> X-ray diffraction, scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. These results support continued interest in such unique structures with substantial configurational entropy and suggest new opportunities for research probing structure-property relationships in high-entropy systems.