Homogeneous Nanoparticles of Multimetallic Phosphides via Precursor Tuning: Ternary and Quaternary M2P Phases (M = Fe, Co, Ni)

Controlling Phase in Colloidal Synthesis

A fundamental precept of chemistry is that properties are manifestations of the elements present and their arrangement in space. Controlling the arrangement of atoms in nanocrystals is not well understood in nanocrystal synthesis, especially in the transition metal chalcogenides and pnictides, which have rich phase spaces. This Perspective will cover some of the recent advances and current challenges. The perspective includes introductions to challenges particular to chalcogenide and pnictide chemistry, the often-convoluted roles of bond dissociation energies and mechanisms by which precursors break down, using very organized methods to map the synthetic phase space, a discussion of polytype control, and challenges in characterization, especially for solving novel structures on the nanoscale and time-resolved studies.

Colloidal Nanoparticles of High Entropy Materials: Capabilities, Challenges, and Opportunities in Synthesis and Characterization

Materials referred to as "high entropy" contain a large number of elements randomly distributed on the lattice sites of a crystalline solid, such that a high configurational entropy is presumed to contribute significantly to their formation and stability. High temperatures are typically required to achieve entropy stabilization, which can make it challenging to synthesize colloidal nanoparticles of high entropy materials. Nonetheless, strategies are emerging for the synthesis of colloidal high entropy nanoparticles, which are of interest for their synergistic properties and unique catalytic functions that arise from the large number of constituent elements and their interactions. In this Perspective, we highlight the classes of materials that have been made as colloidal high entropy nanoparticles as well as insights into the synthetic methods and the pathways by which they form. We then discuss the concept of "high entropy" within the context of colloidal materials synthesized at much lower temperatures than are typically required for entropy to drive their formation. Next, we identify and address challenges and opportunities in the field of high entropy nanoparticle synthesis. We emphasize aspects of materials characterization that are especially important to consider for nanoparticles of high entropy materials, including powder X-ray diffraction and elemental mapping with scanning transmission electron microscopy, which are among the most commonly used techniques in laboratory settings. Finally, we share perspectives on emerging opportunities and future directions involving colloidal nanoparticles of high entropy materials, with an emphasis on synthesis, characterization, and fundamental knowledge that is needed for anticipated advances in key application areas.