Phase stability of high entropy oxides: A critical review

Utilizing High-Capacity Spinel-Structured High-Entropy Oxide (CrMnFeCoCu)3O4 as a Graphite Alternative in Lithium-Ion Batteries

“…These parameters suggest that the secondary phase is based on CuO. In contrast to other studies [43], which report a single-phase spinel structure for this composition, the authors employed a hydrothermal synthesis route followed by calcination at a low temperature of 700 • C. According to other works [29,38,44], copper can segregate at high temperatures (above 1212 K, 939 • C) and form CuO separately from other oxides during slow cooling processes. Liu et al [45] observed similar CuO segregation when preparing HEO with a similar composition of CrFeCoNiCu.…”

Assessing Phase Stability in High-Entropy Materials by Design of Experiments: The Case of the (Mg,Ni,Co,Cu,Zn)O System

“…High-entropy oxides generally present five or more principal elements in near-equiatomic ratios and a configurational entropy of at least 1.609 R per mole of atoms . The first example of a HEO, Mg 0.20 Ni 0.20 Co 0.20 Cu 0.20 Zn 0.20 O, showed a rock salt (RS) structure and was followed by several other oxides presenting fluorite, − perovskite, − pyrochlore, − spinel, − and other crystal structures. − These materials aroused a great deal of interest because their ample compositional flexibility offers the possibility of introducing specific chemical elements into a crystal structure that generally does not allow to host them. This possibility often results in the appearance of new and unexpected functional properties.…”

“…Only in a few cases have compositions deviating from this assumption been reported. In these cases, the compositions of interest were identified through a process of trial and error or adjusting the molar fraction of one element at the expense of others. ,, This approach, defined as the OVAT (one variable at a time) strategy, focuses on the effect of a single element at a time, neglecting any secondary interaction that might be significant in a multielement system. Such a strategy, however, cannot be reliably applied to high-entropy systems as it would require too many experiments.…”

“…Most investigations of HEOs, regardless of the crystal structure involved, assume optimal characteristics at the equimolar composition, where the configuration entropy is the highest . Only in a few cases have compositions deviating from this assumption been reported.…”

A chemometric approach for the design of lanthanum-based high entropy perovskite oxides

“…7,10,11 This entropy effectively compensates for any positive enthalpic contributions, showcasing the pivotal influence of configurational entropy in stabilizing these high-entropy materials. 12,13 The configurational entropy of a system experiences a notable increase as the number of different elements distributed over the cation lattice site rises, reaching its maximum when all constituent elements are present in equimolar amounts. 14 Beyond the intriguing structural implications, this distinct design concept not only highlights the significance of configurational entropy but also presents an opportunity for fine-tuning of materials functional properties.…”