Designing Polar and Magnetic Oxides: Zn2FeTaO6 - in Search of Multiferroics

Polar oxides are technically of great interest but difficult to prepare. Our recent discoveries predicted that polar oxides can be synthesized in the corundum-derivative A2BB′O6 family with unusually small cations at the A-site and a d0 electron configuration ion at B′-site. When magnetic transition-metal ions are incorporated more interesting polar magnetic oxides can form. In this work we experimentally verified this prediction and prepared LiNbO3 (LN)-type polar magnetic Zn2FeTaO6 via high pressure and temperature synthesis. The crystal structure analysis indicates highly distorted ZnO6 and (Fe/Ta)O6 octahedra, and an estimated spontaneous polarization (PS) of ∼50 μC/cm2 along the c-axis was obtained from point charge model calculations. Zn2Fe3+Ta5+O6 has a lower magnetic transition temperature (TN ∼ 22 K) than the Mn2FeTaO6 analogue but is less conductive. The dielectric and polarization measurements indicate a potentially switchable component

Designing Polar and Magnetic Oxides: Zn2FeTaO6 - in Search of Multiferroics

Polar oxides are technically of great interest but difficult to prepare. Our recent discoveries predicted that polar oxides can be synthesized in the corundum-derivative A2BB′O6 family with unusually small cations at the A-site and a d0 electron configuration ion at B′-site. When magnetic transition-metal ions are incorporated more interesting polar magnetic oxides can form. In this work we experimentally verified this prediction and prepared LiNbO3 (LN)-type polar magnetic Zn2FeTaO6 via high pressure and temperature synthesis. The crystal structure analysis indicates highly distorted ZnO6 and (Fe/Ta)O6 octahedra, and an estimated spontaneous polarization (PS) of ∼50 μC/cm2 along the c-axis was obtained from point charge model calculations. Zn2Fe3+Ta5+O6 has a lower magnetic transition temperature (TN ∼ 22 K) than the Mn2FeTaO6 analogue but is less conductive. The dielectric and polarization measurements indicate a potentially switchable component

Polar and Magnetic Mn2FeMO6 (M = Nb, Ta) with LiNbO3-type Structure - High Pressure Synthesis

Polar oxides are of much interest in materials science and engineering. Their symmetry-dependent properties such as ferroelectricity/multiferroics, piezoelectricity, pyroelectricity, and second-order harmonic generation (SHG) effect are important for technological applications. However, polar crystal design and synthesis is challenging, because multiple effects, such as steric or dipole-dipole interactions, typically combine to form non-polar structures; so the number of known polar materials, especially polar magnetoelectric materials, is still severely restricted. Therefore, it is necessary for the material science community to develop new strategies to create these materials

Magnetostriction-polarization coupling in multiferroic Mn2MnWO6

Double corundum-related polar magnets are promising materials for multiferroic and magnetoelectric applications in spintronics. However, their design and synthesis is a challenge, and magnetoelectric coupling has only been observed in Ni3TeO6 among the known double corundum compounds to date. Here we address the high-pressure synthesis of a new polar and antiferromagnetic corundum derivative Mn2MnWO6, which adopts the Ni3TeO6-type structure with low temperature first-order field-induced metamagnetic phase transitions (T N = 58 K) and high spontaneous polarization (~ 63.3 μC·cm−2). The magnetostriction-polarization coupling in Mn2MnWO6 is evidenced by second harmonic generation effect, and corroborated by magnetic-field-dependent pyroresponse behavior, which together with the magnetic-field-dependent polarization and dielectric measurements, qualitatively indicate magnetoelectric coupling. Piezoresponse force microscopy imaging and spectroscopy studies on Mn2MnWO6 show switchable polarization, which motivates further exploration on magnetoelectric effect in single crystal/thin film specimens

Chemical tunnel-splitting-engineering in a dysprosium-based molecular nanomagnet

Total control over the electronic spin relaxation in molecular nanomagnets is the ultimate goal in the design of new molecules with evermore realizable applications in spin-based devices. For single-ion lanthanide systems, with strong spin-orbit coupling, the potential applications are linked to the energetic structure of the crystal field levels and quantum tunneling within the ground state. Structural engineering of the timescale of these tunneling events via appropriate design of crystal fields represents a fundamental challenge for the synthetic chemist, since tunnel splittings are expected to be suppressed by crystal field environments with sufficiently high-order symmetry. Here, we report the long missing study of the effect of a non-linear (C4) to pseudo-linear (D4d) change in crystal field symmetry in an otherwise chemically unaltered dysprosium complex. From a purely experimental study of crystal field levels and electronic spin dynamics at milliKelvin temperatures, we demonstrate the ensuing threefold reduction of the tunnel splitting.M.A.S., U.B.H., K.L., and J.Be. acknowledge financial support from the Danish Research Councils for Independent Research (12-125226). M.A.S., U.B.H., M.R, and K.L. acknowledge DANSCATT for financial support for the neutron scattering experiments. For the experiments conducted at FRM II, this project has received funding from the European Union’s 7th Framework Programme for research, technological development and demonstration under the NMI3-II Grant number 283883. M.A.S. thanks the Oticon Foundation (16-2669), and the Augustinus Foundation (16-2917) for financial support in relation to a research stay at Institut für Physikalische Chemie, Universität Stuttgart, Germany. M.P. and J.v.S. thank the DFG for funding (SL104/5-1). K.S.P. thanks the Danish Research Council for Independent Research for a DFF-Sapere Aude Research Talent grant (4090-00201). E.B., A.A, and, J.Ba. acknowledge the financial support of Spanish MINECO project MAT2017-83468-R. M.J. acknowledges the Swiss National Science Foundation.Peer reviewe

Highly active and stable OER electrocatalysts derived from Sr2MIrO6 for proton exchange membrane water electrolyzers

Proton exchange membrane water electrolysis is a promising technology to produce green hydrogen from renewables, as it can efficiently achieve high current densities. Lowering iridium amount in oxygen evolution reaction electrocatalysts is critical for achieving cost-effective production of green hydrogen. In this work, we develop catalysts from Ir double perovskites. Sr2CaIrO6 achieves 10 mA cm−2 at only 1.48 V. The surface of the perovskite reconstructs when immersed in an acidic electrolyte and during the first catalytic cycles, resulting in a stable surface conformed by short-range order edge-sharing IrO6 octahedra arranged in an open structure responsible for the high performance. A proton exchange membrane water electrolysis cell is developed with Sr2CaIrO6 as anode and low Ir loading (0.4 mgIr cm−2). The cell achieves 2.40 V at 6 A cm−2 (overload) and no loss in performance at a constant 2 A cm−2 (nominal load). Thus, reducing Ir use without compromising efficiency and lifetim