Inside E-MRS World - Vol. 3 / No. 1 - June 2024
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EDITORIAL
Exploring Unconventional Materials - an Actual Challenge
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E-MRS Spring and Fall meetings offer the possibility to access symposia with diverse audiences, from the smallest to the largest, open to all domains of materials science. In inorganic chemistry, oxides represent a very large class of materials, mostly due to their natural stability, where the materials chemist is able to design new compositions by substitutions in the cationic network. Many new compositions and subsequent properties and applications have resulted in the past decades.
However, non-oxide chemistry gathers a smaller community of researchers compared to that of oxides, with fewer compounds. Tailoring the anionic network leads to exciting challenges. As an example, starting from the well-known ceramic BaTiO3, several oxynitride perovskite compositions were prepared by appropriate cross-substitutions – in terms of charges and element size – in both cationic and anionic sublattices. Many perovskite compositions such as LaTiO2N, LaTaON2, and derivatives were studied to uncover dielectric properties.
Introducing the concept of mixed-anion compounds opens the way to a host of possible combinations among O, H, C, N, F, S, Cl,… anions in crystalline and glassy materials. In particular, comparing oxynitrides and oxides highlights several features of the N/O substitution: an increase in the formal anionic charge, a higher cross-linking density in glasses, a stronger covalency, a reducing behaviour due to the N3-/N0 redox couple, and modified acid-base properties. A suitable combination between anions will allow tuning the properties in many applications. But such chemistry is far from being as easy as that for producing oxides in air. Here syntheses require the control of more complex solid or solid-gas reactions. More complexity also in the chemical (stability, elemental analyses,…) and structural characterisations (X-ray/neutron diffraction, anionic (dis)ordering,…) make mixed-anion compounds stimulating materials to study.
Among oxynitrides, oxyhalides, oxysulfides, and oxyhydrides, these unconventional materials are currently attracting a lot of attention in several strategic fields related to energy and environment. Examples include phosphors, pigments, catalysts (heterogeneous catalysis, visible photocatalysis, electrocatalysis,…), battery materials, and dielectrics, as well as in the areas of superconductivity, magnetism, and thermoelectricity.
Nevertheless, to achieve real advances, only sustained and regular investments in synthesis will enable the emergence of new functional materials that meet the requirements of 21st-century applications.
To learn more about this promising class of materials, I recommend the recent book, Mixed-anion Compounds by Hiroshi Kageyama; Hiraku Ogino; Tong Zhu; Tetsuya Hasegawa (Royal Society of Chemistry, 2024), 272 pages. https://doi.org/10.1039/9781839166372.
Franck TESSIER
Vice President
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