Novel electronic and magnetic properties of high Entropy Oxides

• Applicant: Professor Dr. Hidenori Takagi
• Subject Area: Synthesis and Properties of Functional Materials
• Term: from 2019 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 431403378

• Final Report Year: 2023

Final Report Abstract

New High-Entropy Materials. Synthesis of New Oxides Controlled by Configuration Entropy Entropy-stabilized oxides are metastable materials typically obtained at high temperatures when configuration entropy plays a crucial role in the chemical reaction. More generally, so-called "high-entropy" oxides can be thermodynamically stable, and are characterized by having a large number of components (at least 5) randomly distributed on a crystalline position. The first oxides of this kind were synthesized in 2015, and our group in Orsay was the first to obtain similar compounds in 2016 and to study their functional properties. Since then, significant interest in these materials has developed. In this project, we had two distinct objectives, related to the complementary expertise of the two participating groups from the University of Paris-Saclay and the University of Stuttgart: discovery of new materials stabilized by entropy or with high entropy; study of their physical properties. Several new compounds were synthesized for the first time and their physical properties were determined. On one hand we observed a great diversity of compounds, and on the other hand, a shared characteristic in the properties of these compounds: the existence of electronic or magnetic correlations despite significant chemical disorder. Transport Properties in High-Entropy Configuration Oxides The essential characteristic of entropy-stabilized compounds is the existence of cations in unusual configurations or structures. This results in physical properties that are difficult to predict. The physical properties of interest that we addressed include thermal conductivity, electrical transport, and magnetism. For the first two, there is a significant interest in thermoelectric compounds, and we obtained for example interesting results in perovskite families of type ACoO3 and pyrochlores of type A2Ir2O7. Regarding magnetism, several important results were obtained: Strong magnetic correlations in ilmenite-type compounds or AMnO3 with a perovskite structure. - Possibilities for adjusting magnetic properties in pyrochlores. - Studies of interactions in spinel-type AV2O4 compounds. We obtained several new compounds, including for example 8 new entropy-stabilized compounds for the Dy2X2O7 pyrochlore structure system, which were identified for the first time. A systematic study of their properties is ongoing. The publications resulting from the project (7 articles published in peer-reviewed international journals, currently 3 articles under revision, and 4 others in preparation) have highlighted the existence of around twenty new compounds and illustrated some interesting physical properties. The NEO project is an international cooperation project (with DFG/Germany) with an exploratory nature aimed at the synthesis and study of the physical properties of a new family of materials, known as "high-entropy" materials, obtained by controlling configuration entropy.

Publications

• New entropy-stabilized oxide with pyrochlore structure: Dy2(Ti0.2Zr0.2Hf0.2Ge0.2Sn0.2)2O7. Journal of Alloys and Compounds, 883, 160773.
  Vayer, Florianne; Decorse, Claudia; Bérardan, David & Dragoe, Nita
  
• «Entropy-stabilized oxides : a new route for materials design» France-Korea joint seminar PHC-STAR, december 8, 2021.
  F. Vayer, C. Decorse, D. Bérardan & N. Dragoe
  
• «The recipe for a new magic potion, an entropy-stabilized pyrochlore Dy2(TiZrSnHfGe)2O7» at #RSCPoster (Royal Society of Chemistry Poster Conference on Twitter), march 3, 2021.
  F. Vayer & C. Decorse
  
• Entropy driven synthesis of new materials. Materials Lab, 1, 1-3.
  Dragoe, Nita
  
• Entropy-stabilized oxide, a new route for the design of geometrically frustrated materials» 11th International Conference on Highly Frustrated Magnetism, Paris, France, July 20-25, 2022.
  F. Vayer, D. Bérardan, N. Dragoe, D. Bounoua, F. Damay, S. Petit, E. Lhotel & C. Decorse
  
• Investigation of the chemical versatility in high‐entropy pyrochlores. Journal of the American Ceramic Society, 106(4), 2601-2621.
  Vayer, Florianne; Decorse, Claudia; Bérardan, David; Dragoe, Diana & Dragoe, Nita
  
• «Entropy-stabilized oxides with pyrochlore structure – synthesis and characterization» 2MIB Doctoral School, ENS Paris-Saclay, Gif sur Yvette, may 25, 2022.
  F. Vayer, C. Decorse, D. Bérardan & N. Dragoe
  
• «Exploration of exotic electronic and magnetic phases in high-entropy oxides» Telluride workshop “THe role of compositional complexity in functional high entropy materials”, Telluride, CO, USA, June 27, 2022.
  T.Takayama, D. Contant, G. McNally, L. Kruty, S. Bette, R. Dinnebier & H. Takagi
  
• Chemical vapor deposition of entropy-stabilized rock-salt type oxide thin films. Materials Letters, 337, 133955.
  Raison, Antoine; Prud'homme, Nathalie; Wang, Wu; Dragoe, Diana & Dragoe, Nita
  
• Magnetic and electrical properties of high-entropy rare-earth manganites. Materials Today Physics, 32, 101026.
  Kumar, Ashutosh; Bérardan, David; Dragoe, Diana; Riviere, Eric; Takayama, Tomohiro; Takagi, Hidenori & Dragoe, Nita
  
• Novel entropy-stabilized fluorite oxides with multifunctional properties. Journal of Materials Chemistry A, 11(26), 14320-14332.
  Kumar, Ashutosh; Bérardan, David; Brisset, Francois; Dragoe, Diana & Dragoe, Nita
  
• Thermoelectric properties of high-entropy rare-earth cobaltates. Journal of Materiomics, 9(1), 191-196.
  Kumar, Ashutosh; Dragoe, Diana; Berardan, David & Dragoe, Nita
  
• “High entropy oxides as new playground for functional materials development”. International Conference on High Entropy Materials ICHEM2023, June 18-22, 2023, Knoxville, Tennessee, USA
  D. Berardan & N. Dragoe