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Interface segregation plays a governing role in nanocrystalline ceramics properties due to the relative increase in the interfacial volume fraction. However, due to the complexity of the detection and quantification of interfacial excesses at the nanoscale, the role of ionic dopants or additives on microstructural evolution and thermodynamics can be easily underestimated. In this work, we address the spatial distribution of Li⁺as a dopant in magnesium aluminate spinel nanoparticles. This is achieved through a novel method for the detection and quantification of Li⁺across the surface, grain boundary, and bulk (crystal lattice). Based on selective lixiviation combined with chemical analysis, we were able to quantify the amount of Li⁺forming surface excess, whereas the quantitative solid‐state nuclear magnetic resonance technique enabled the quantification of Li⁺segregated in the grain boundaries and dissolved in the lattice. This comprehensive understanding of the Li⁺distribution across the nanoparticles makes possible an unprecedented interpretation of coarsening and sintering, with a clear correlation between the microstructure and the Li⁺distribution. Although the work focuses on MgAl₂O₄, the proposed combination of techniques is expected to have a positive impact on the understanding of other multicomponent nanoscale systems. 

Hematite nanostructures are strong candidates for the development of sustainable water splitting technologies. However, major challenges exist in improving charge density and minimizing charge recombination rates for a competitive photoelectrochemical performance based on hematite without compromising sustainability aspects. Here we develop a synthetic strategy to leverage earth-abundant Al3+ and Zr4+ in a dual-chemical modification to synergistically minimize small polaron effects and interfacial charge recombination. The solution-based method simultaneously induces Al3+ doping of the hematite crystal lattice while Zr4+ forms interfacial excess, creating a single-phased homogeneous nanostructured thin film. The engineered photoanode increased photocurrent from 0.7 mA cm-2 for pristine hematite up to 4.5 mA cm-2 at 1.23 V and beyond 6.0 mA cm-2 when applying an overpotential of 300 mV under simulated sunlight illumination (100 mW cm-2). The results demonstrate the potential of dual-modification design using solution-based processes to enable sustainable energy technologies.