The hypotheses underpinning this AMANTS project are 1) that a variety of novel A-site based Mn oxide perovskites and related phases can be recovered from high pressure synthesis, and that these new materials will have interesting and potentially useful properties. And 2) that the new playground of “hard-soft” synthesis has an important role on the new A-site Mn2+ materials by modifying their anion lattices.
The main objectives of the AMANTS project are:<br />O1 – to synthesise new A-site Mn2+A2BB’O6 complex oxides, establish their structures, and explore magnetic and other physical properties.<br />O2 – to synthesise double-double perovskites based upon the newly-discovered MnRMnSbO6 structure type, and explore magnetic and other physical properties.<br />O3 – to modify the anion lattices by “hard-soft” chemistry or direct HP synthesis of new Mn2+ A-site manganites with mixed anions.<br />O4 – to obtain high temperature robust magnets and spintronic materials with enhanced properties due to Mn2+ presence on the A-site and coupling with B.<br />O5 – to discover new magneto-electric materials based on A-site Mn2+.<br /><br />The main issues encountered so far are:<br />Due to CoViD protocols, restricted access to laboratories and not full presence of the whole technical personal have somehow slow down the development of the project, e.g. some equipment not being operational or delays in supplies necessary for the high-pressure facility (delivery of the cells to run the experiment took 6 months). Along the mixed anions line of research of the AMANTS project, the inaccessibility to the precursors have made us focus on the other lines of the project. This will be performed in the second part of the project thanks to the collaboration with the Universidad Complutense de Madrid. <br />The hiring of the M2 for three months has been delayed until the full calibration of the press was performed (October 2021). He/she will be hired in 2022.
High-Pressure Synthesis: The new high-pressure facility (Walker type press) has been installed (November 2020) and calibrated (2021) in a joint effort with colleagues from UMET (CNRS UMR 8207). The experimental capabilities of this machine are temperatures up to 2500 °C and pressures up to 23 GPa. The calibration process has been an arduous work, with the requirement to prepare the machine with a compound that presents an electrical transition at a known pressure. We have used Bi (transitions at 2.6, 2.8 and 7.7 GPa), ZnTe (9.6 and 12.1 GPa) for the 14/8 setup (able to reach 16 GPa). For the smaller 10/5 setup (able to reach 23 GPa) we have used Bi, ZnS (15 GPa) and GaAs (18.5 GPa).
Solid state synthesis: Many precursors are ready to keep using the high-pressure lab. Along the new triple A-site manganites series, we have prepared Mn4-dMdX2O9 with M = Fe, Co, Ni, d = 0, 1, 2, 3 and 4 and X = Nb and Ta. We have also obtained some Neutron beamtime at the ILL @ Grenoble. We are continuing on the characterization and analysis of the results and they will be probably ready for a publication at the beginning of 2022. We have also prepared Mn11Ta4O21 and re-analyzed as a A-site manganite hexagonal perovskite, it shows two magnetic transitions and magnetodielectric coupling. This has been published in 2020.
Mixed anion synthesis: The mixed anions part of the project has been momentarily paused. At the moment our ammonia furnace is not fully operational. This is a more administrative issue in terms of safety due to the ammonia gas. We are re-starting a collaboration with the Universidad Complutense de Madrid (Spain) in order to obtain the precursors required for this part of the project.
Characterization: The structural and properties characterizations of the obtained materials has been fruitful. We have successfully solved the crystal structures of new compounds (e.g. Mn3MnX2O9, X = Nb and Ta) by single crystal or synchrotron or neutron diffraction at in house, ALBA (Spain) or ILL (France) facilities respectively.
Concerning the properties characterization, we have implemented the protocols for magnetodielectric coupling measurements between the PPMS and our in-house probe attached to the LCR meter. We have also succeeded in ensuring funding for a Ferroelectric probe from Radiant, which will couple with our PPMS for measuring polarization vs electric field loops between 4-400 K and 0-7 T.
The Walker-type press has already started to produce results. We have obtained a new polymorph in line with the AMANTS project, namely Mn3MnX2O9 (X = Nb and Ta). This novel family of triple A-site manganites show complex magnetic properties and magnetodielectric coupling. Two publications have been obtained from this set of materials.
We have also obtained some Neutron beamtime at the ILL @ Grenoble. We are continuing on the characterization and analysis of the results and they will be probably ready for a publication at the beginning of 2022.
We have also prepared Mn11Ta4O21 and re-analyzed as a A-site manganite hexagonal perovskite, it shows two magnetic transitions and magnetodielectric coupling. This has been published in 2020.
The focus of the AMANTS project is shifting towards the newly discovered triple perovskite A-site manganite family Mn3MnX2O9 (X = Nb or Ta) and substitute Co, Fe and Ni to expand what it is chemically possible and find new compounds.
1. Á. M. Arévalo-López, E. Solana-Madruga, C. Aguilar-Maldonado, C. Ritter, O. Mentre and J. P. Attfield. Magnetic frustration in the high-pressure Mn2MnTeO6 (Mn3TeO6-II) double perovskite. Chem. Commun. 55 (2019) 14470
2. C. Aguilar-Maldonado, E. P. Arevalo-Lopez, C. Ritter, O. Mentre and Á. M. Arévalo-López. Magnetic Structures of Mn11Ta4O21 and Interpretation as an Hexagonal A-site Manganite. Inorg. Chem. 59 (2020) 13128
3. E. Solana-Madruga, C. Aguilar-Maldonado, C. Ritter, M. Huve, O. Mentre, J. P. Attfield and Á. M. Arévalo-López. Complex magnetism in Ni3TeO6-type Co3TeO6 and high-pressure polymorphs of Mn3-xCoxTeO6 solid solutions. Chem. Commun. 57 (2021) 2511
4. E. Solana-Madruga, C. Ritter, C. Aguilar-Maldonado, O. Mentre, J. P. Attfield and Á. M. Arévalo-López. Mn3MnNb2O9 high-pressure triple perovskite with 1:2 B-site order and modulated spins. Chem. Commun. 57 (2021) 8441
5. E. Solana-Madruga, C. Ritter, O. Mentre and Á. M. Arévalo-López. Spin structures and band gap reduction of high- pressure triple perovskite Mn3MnTa2O9. J. Mater. Chem C. 2021 Advance Article
The discovery of new materials with appealing functional properties e.g. superconductivity, magnetoresistance or multiferroicity is challenging and such properties are often observed in complex oxides containing transition metals in intermediate or unusual oxidation states which must be stabilised under special synthetic conditions.
High-pressure and temperature synthesis ("hard" chemistry) is a powerful tool for stabilising materials with unique structures and properties and one can manipulate and tune those structures, and therefore their properties, by modifying their anion lattices with “soft” reactions. Hence, “hard-soft” oxide chemistry is appealing as synthetic route for new functional materials. This project will build on recent discoveries on placing transition metals at the A-sites of A2BB'O6 complex oxides with high pressure and the use of "hard-soft" chemistry, offering new possibilities for discovery of exciting functional materials.
Specifically, we will focus on the insertion of Mn2+ on the A-site. The “hard-soft” approach will help on structural and properties tuning towards functional oxides at ambient conditions.
Monsieur Angel Arevalo-Lopez (Unité de Catalyse et de Chimie du Solide)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
UCCS Unité de Catalyse et de Chimie du Solide
Help of the ANR 205,056 euros
Beginning and duration of the scientific project: September 2019 - 48 Months