Chemical Short Range Order in Complex Functional Ceramics

Complex functional ceramics (CFCs) offer unique physicochemical properties across diverse promising applications in the fields of energy storage, chemical sensing, catalysis, magneto-electronics, and biomedicine, by their finely controllable chemical compositions and unique structural diversity. CFCs accommodate high levels of atomic disorder and lattice distortion, where the chemical short-range order (CSRO) of cations (or anions) decorating crystal structure sublattices may play special roles in directing structure-property trends. This work explores the relationship between CSRO and specific functional properties in three families of CFCs with combined experimental and theoretical approaches. First, our systematic exploration of local structure across the A cation size series (from the larger Ba to the smaller Ca) of ATaO₂N (A=Ba, Sr, Ca) perovskite oxynitrides determines that local cis ordering and Ta off-centering play decreasing roles in overall lattice stability, overshadowed by the stabilizing effects of octahedral tilting. Second, we explore the sensitivity of ferrimagnetism to local cation order in spinel CFCs with compositions AFe₂O₄ (where A includes different combinations of Mg, Fe, Co, Ni, Cu, Mn, and Zn). The distinct populations of Fe and other magnetic cations on tetrahedral and octahedral sites in the materials are found to be impacted by thermal processing history and manifest in variation in the prevalence and propagation of local spin clusters, as revealed by detailed magnetometry data. Finally, we systematically examine the CSRO in a large new family of nano compositionally complex spinel oxides ACo₂O₄ (where A includes different combinations of Mn, Fe, Cu, Zn, Mg, and Ni), prepared by an eco-friendly low-temperature soft-templating reaction route. Thermal processing history is shown to significantly influence various characteristics in the series, including phase purity, particle morphology, particle size, and the degree of cation site inversion. The inclusion or exclusion of specific cations is revealed to be an additional key design consideration. These characteristics are demonstrated to influence the family's electrocatalytic activities and magnetic properties, notably revealing promising bifunctional oxygen evolution reaction and reduction reaction performance. These efforts promote design principles and processing strategies for functional property tuning in CFCs and point to the importance and challenges of atomic structure characterization matching their complexity.