Strukturelle, elektronische und magnetischen Eigenschaften von Oxyden unter hohen Drücken und Temperaturen: neue Polymorphe, Einsichten und Einsatzmöglichkeiten
Herstellung und Eigenschaften von Funktionsmaterialien
Zusammenfassung der Projektergebnisse
In this project, we have experimentally investigated the structural and phase stability of a number of the key transition metal oxides in the extreme conditions of high pressures and temperatures. We have employed both i) diamond anvil cells with a possibility of laser heating enabling in situ studies of phase transformations in oxides under high-pressure high-temperature (HP-HT) conditions, and ii) largevolume multi-anvil cells enabling a HP-HT synthesis of sizable pieces of new oxide polymorphs. In particular, we investigated several binary systems as Ti2O3, Mn2O3, V2O3, Fe2O3, Sc2O3, and Fe4O5, in which the transition metal cations (Ti, Mn, V, Fe) may be in different oxidation states, thereby promising more interesting physical properties. In addition, we explored how a minor cross-doping can affect the properties of their pseudo-binary solid solutions. We have obtained a number of remarkable results which present a significant interest and importance for basic physical and chemical sciences, and which could potentially find some industrial applications in the future. Below, we describe some of our findings for three the most interesting newly-discovered polymorphs. 1. Golden Ti2O3 with Th2S3-type crystal structure. We found that conventional corundum-structured Ti2O3 under moderate HP-HT conditions converts to ultra-dense Th2S3-type polymorph of golden colour. We investigated the electronic transport, structural, vibrational and other properties of the golden Ti2O3 both at ambient and high pressures. We found that the golden Ti2O3 is a semiconductor with a band gap value of about 0.1-0.2 eV. The high-pressure study unravelled that the Ti cations in this simple sesquioxide are prone to multiple valence states (+2,+3,+4) instead of the only +3 in the corundum-type phase. Our HP-HT investigations indicated that the physical properties of the golden Ti2O3 may depend on the synthesis conditions. This fact hints that synthesis conditions can to some extent control the amount of Ti4+ ions in recovered samples. This finding suggests that the golden Ti2O3 with stress-controlled physical properties may be promising for industrial applications, e.g., as a tuneable element in thin epitaxial films. 2. The perovskite-type Mn2O3. We found that under certain moderate HP-HT conditions, a simple conventional cubic-bixbyite Mn2O3 transforms into a new phase with a double perovskite structure as MnMn3Mn4O12 with a triclinic symmetry. This phase is readily recoverable at ambient conditions. In the course of this phase transition, the Mn ions were subjected to partial charge disproportionation: 2Mn3+→Mn2++Mn4+ that enabled the Mn ions to fill crystallographically different sites in the perovskite structure. This result is of significant importance for science and technology of perovskites. We have established that the the perovskite-type Mn2O3 is a multiferroic, and to some extend it may be considered as a parent material for series of AMn7O12 multiferroics. In addition, we have unraveled that the perovskite-type Mn2O3 is characterized by a direct and narrow band gap of 0.45 eV. This makes it particularly promising for applications in semiconductor industry, e.g., in IR detectors. Compared to traditional chalcogenide semiconductors with similar band gap values, like PbTe, PbSe, HgCdTe, the perovskite-type Mn2O3 comprising non-toxic, earth-abundant and non-expensive elements, is much more incompressible and stronger than those. 3. High-pressure iron oxide, Fe4O5. We synthesized high-quality single crystals of this iron oxide and discovered that near 150 K it undergoes an unprecedented charge-ordering transition of a metal-insulator-type with competing dimeric and trimeric ordering in linear chains of octahedrallycoordinated iron. This transition seems to be even more bizarre, than the Verwey transition in magnetite at 120 K. We found that application of moderate high pressure enhances the chargeordering temperature in Fe4O5, and it transforms to another charge-ordered phase. In general, we demonstrated that Fe4O5 is even more exciting prototype system to study the Fe2+/Fe3+ interactions and charge ordering in mix-valent iron oxides, than the above magnetite. Thus, our project significantly contributed to the knowledge of simple transition metal oxides and related materials. Additionally, the accomplishment of this project enabled to grasp new challenges for these and related systems and new directions in their future investigations.
Projektbezogene Publikationen (Auswahl)
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(2012): High-pressure cycling of hematite (-Fe2O3): Nanostructuring, in-situ electronic transport and possible charge disproportionation. Physical Review B 86, 205131
Ovsyannikov, S.V., Morozova, N.V., Karkin, A.E. and Shchennikov, V.V.
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(2012): Pressure-temperature phase diagram of Ti2O3 and physical properties in the golden Th2S3-type phase. Physical Review B 86, 024106
Ovsyannikov, S.V., Wu, X., Karkin, A.E., Shchennikov, V. V., Manthilake, G. M.
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(2013): Anomalous compression and new high-pressure phases of vanadium sesquioxide, V2O3. J. Phys.: Condens. Matter 25, 385401
Ovsyannikov, S. V., Trots, D. M., Kurnosov, A. V., Morgenroth, W., Liermann, H.-P., and Dubrovinsky, L.
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(2013): High-pressure behavior of structural, optical, and electronic transport properties of the golden Th2S3-type Ti2O3, Physical Review B 88, 184106
Ovsyannikov, S.V., Wu, X., Garbarino, G., Núñez-Regueiro, M., Shchennikov, V. V., Khmeleva, J. A., Karkin, A. E., Dubrovinskaia, N., Dubrovinsky, L.
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(2013): Perovskite-like Mn2O3: a path to new manganites, Angewandte Chemie Int. Ed. 52, 1494-1498
Ovsyannikov, S.V., Abakumov, A.M., Tsirlin, A.A., Schnelle, W., Egoavil, R., Verbeeck, J., Van Tendeloo, G., Glazyrin, K., Hanfland, M., Dubrovinsky, L.
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(2014): A hard oxide semiconductor with a direct and narrow bandgap and switchable p-n electrical conduction. Advanced Materials 26, 8185–8191
Ovsyannikov, S. V., Karkin, A. E., Morozova, N. V., Shchennikov, V. V., Bykova, E., Abakumov, A. M., Tsirlin, A. A., Glazyrin, K. V., and L. Dubrovinsky
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(2015): Structural and vibrational properties of single crystals of Scandia, Sc2O3 under high pressure. Journal of Applied Physics 118, 165901
Ovsyannikov, S. V., Bykova, E., Bykov, M., Wenz, M. D., Pakhomova, A. S., Glazyrin, K., Liermann, H.-P., Dubrovinsky, L.
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(2016): Charge ordering transition in iron oxide Fe4O5 involving competing dimer and trimer formation. Nature Chemistry 8, 501-508
Ovsyannikov, S. V., Bykov, M., Bykova, E., Kozlenko, D. P., Tsirlin, A. A., Karkin, A. E., Shchennikov, V. V., Kichanov, S. E., Gou, H., Abakumov, A. M., Egoavil, R., Verbeeck, J., McCammon, C., Dyadkin, V., Chernyshov, D., van Smaalen, S., Dubrovinsky, L. S.
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(2016): Discovery of Fe7O9: a new iron oxide with a complex monoclinic structure. Scientific Reports 6, 32852
Sinmyo, R., Bykova, E., Ovsyannikov, S. V., McCammon, C., Kupenko, I., Ismailova, L., Dubrovinsky, L.
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(2018): Spin-induced multiferroicity in the binary perovskite manganite Mn2O3. Nature Communications 9, 2996
Cong, J., Zhai, K., Chai, Y., Shang, D., Khalyavin, D. D., Johnson, R. D., Kozlenko, D. P., Kichanov, S. E., Abakumov, A. M., Tsirlin, A. A., Dubrovinsky, L., Xu, X., Sheng, Z., Ovsyannikov, S. V., Sun, Y.
