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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 (TN = 58 K) and high spontaneous polarization (~ 63.3 μC·cm-2). The magnetostrictionpolarization 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. [ABSTRACT FROM AUTHOR]

Pb2MnTeO6, a new double perovskite, was synthesized. Its crystal structure was determined by synchrotron X-ray and powder neutron diffraction. Pb2MnTeO6 is monoclinic (I2/m) at room temperature with a regular arrangement of all the cations in their polyhedra. However, when the temperature is lowered to ∼120 K it undergoes a phase transition from I2/m to C2/c structure. This transition is accompanied by a displacement of the Pb atoms from the center of their polyhedra due to the 6s² lone-pair electrons, together with a surprising off-centering of Mn2+ (d5) magnetic cations. This strong first-order phase transition is also evidenced by specific heat, dielectric, Raman, and infrared spectroscopy measurements. The magnetic characterizations indicate an anti-ferromagnetic (AFM) order below TN ≈ 20 K; analysis of powder neutron diffraction data confirms the magnetic structure with propagation vector k = (0 1 0) and collinear AFM spins. The observed jump in dielectric permittivity near ∼150 K implies possible anti-ferroelectric behavior; however, the absence of switching suggests that Pb2MnTeO6 can only be antipolar. First-principle calculations confirmed that the crystal and magnetic structures determined are locally stable and that anti-ferroelectric switching is unlikely to be observed in Pb2MnTeO6. [ABSTRACT FROM AUTHOR]

The preparation, crystal structure and magnetic properties of Sr2BIrO6 (B = In, Sc, Fe, Co or Ti) oxides are reported. For B = Sc, Fe, Co or In materials, X-ray and neutron powder diffraction (NPD) studies confirm the presence of 1:1 B-ordered perovskite-like structures crystallizing in the monoclinic I2/ m and P21/ n space groups, with unit-cell parameters a ≈ √2 a0, b ≈ √2 a0, c ≈ 2 a0 and β ≈ 90°. Sr2TiIrO6 is described as a disordered perovskite with orthorhombic symmetry in the Pbnm space group. For B = Fe and Co, low-temperature NPD data and magnetic measurements indicate the existence of an antiferromagnetic structure resulting from the Fe3+/Co3+ magnetic moment interaction. X-ray absorption spectroscopy corroborates that the oxidation states of B and Ir are 3+ and 5+, respectively. The bond lengths and other structural features are discussed in the framework of other recently reported iridium double perovskites where iridium adopts tetravalent, pentavalent and hexavalent oxidation states, and in the wider context of Sr double perovskites. [ABSTRACT FROM AUTHOR]

The first transition-metal-only double perovskite compound, Mn2+2Fe3+Re5+O6, with 17 unpaired d electrons displays ferrimagnetic ordering up to 520 K and a giant positive magnetoresistance of up to 220 % at 5 K and 8 T. These properties result from the ferrimagnetically coupled Fe and Re sublattice and are affected by a two-to-one magnetic-structure transition of the Mn sublattice when a magnetic field is applied. Theoretical calculations indicate that the half-metallic state can be mainly attributed to the spin polarization of the Fe and Re sites. [ABSTRACT FROM AUTHOR]

The first transition-metal-only double perovskite compound, Mn2+2Fe3+Re5+O6, with 17 unpaired d electrons displays ferrimagnetic ordering up to 520 K and a giant positive magnetoresistance of up to 220 % at 5 K and 8 T. These properties result from the ferrimagnetically coupled Fe and Re sublattice and are affected by a two-to-one magnetic-structure transition of the Mn sublattice when a magnetic field is applied. Theoretical calculations indicate that the half-metallic state can be mainly attributed to the spin polarization of the Fe and Re sites. [ABSTRACT FROM AUTHOR]

The first transition-metal-only double perovskite compound, Mn2+2Fe3+Re5+O6, with 17 unpaired d electrons displays ferrimagnetic ordering up to 520 K and a giant positive magnetoresistance of up to 220 % at 5 K and 8 T. These properties result from the ferrimagnetically coupled Fe and Re sublattice and are affected by a two-to-one magnetic-structure transition of the Mn sublattice when a magnetic field is applied. Theoretical calculations indicate that the half-metallic state can be mainly attributed to the spin polarization of the Fe and Re sites. [ABSTRACT FROM AUTHOR]

The first transition-metal-only double perovskite compound, Mn2+2Fe3+Re5+O6, with 17 unpaired d electrons displays ferrimagnetic ordering up to 520 K and a giant positive magnetoresistance of up to 220 % at 5 K and 8 T. These properties result from the ferrimagnetically coupled Fe and Re sublattice and are affected by a two-to-one magnetic-structure transition of the Mn sublattice when a magnetic field is applied. Theoretical calculations indicate that the half-metallic state can be mainly attributed to the spin polarization of the Fe and Re sites. [ABSTRACT FROM AUTHOR]

Pb2MReO6(M = Co, Cr) perovskites were preparedby high pressure–high temperature method. Rietveld refinementsof synchrotron powder X-ray diffraction show that the crystal structureof Pb2CoReO6is trigonal (space group R-3) with almost complete ordering of Co and Re cations,while Pb2CrReO6(space group Pm-3m) is a cubic perovskite with one single site for Cr and Re atoms.The difference between the symmetry and the degree of order was furtherclarified by X-ray absorption spectroscopy that establishes formaloxidation states in these phases as Pb2Co2+Re6+O6and Pb2Cr3+Re5+O6. Pb2CrReO6is a simple perovskitewith a high magnetic ordering temperature of 643 K. Pb2CoReO6is a double perovskite with −23% high fieldnegative magnetoresistance at 10 K and 9 T. First-principles calculationsof Pb2CoReO6indicate a half metallic electronicstructure. [ABSTRACT FROM AUTHOR]

CsTlCl3 and CsTlF3 perovskites have been theoretically predicted to be superconductors when properly hole-doped. Both compounds have been previously prepared as pure compounds: CsTlCl3 in a tetragonal (I4/m) and a cubic (Fm3m) perovskite polymorph and CsTlF3 as a cubic perovskite (Fm3m). In this work, substitution of Tl in CsTlCl3 with Hg is reported, in an attempt to hole-dope the system and induce superconductivity. The whole series CsTl1-xHgxCl3 (x = 0.0, 0.1, 0.2, 0.4, 0.6, and 0.8) was prepared. CsTl0.9Hg0.1Cl3 is tetragonal as the more stable phase of CsTlCl3. However, CsTl0.8Hg0.2Cl3 is already cubic with the space group Fm3m and with two different positions for Tl+ and Tl3+. For x = 0.4 and 0.5, solid solutions could not be formed. For x ≥ 0.6, the samples are primitive cubic perovskites with one crystallographic position for Tl+, Tl3+, and Hg2+. All of the samples formed are insulating, and there is no signature of superconductivity. X-ray absorption spectroscopy indicates that all of the samples have a mixed-valence state of Tl+ and Tl3+. Raman spectroscopy shows the presence of the active Tl-Cl-Tl stretching mode over the whole series and the intensity of the Tl-Cl-Hg mode increases with increasing Hg content. First-principle calculations confirmed that the phases are insulators in their ground state and that Hg is not a good dopant in the search for superconductivity in this system. [ABSTRACT FROM AUTHOR]

TheAA′3B4O12-type quadrupleperovskite LaCu3Ir4O12prepared athigh pressure (9 GPa) and temperature (1523 K) crystallizes in cubicsymmetry (Im3̅, a= 7.52418(3)Å) with square planar CuO4and octahedral IrO6coordination as established from synchrotron powder X-raydiffraction studies. Both crystal structure and X-ray absorption nearedge spectroscopy analyses indicate formal oxidation states of LaCu2+3Ir3.75+4O12.The temperature dependence of resistivity of LaCu3Ir4O12is metallic down to 10 K, with Femi-liquidbehavior above T* ∼ 155 K, and non-Fermi-liquidbehavior below T*. The two-fluid behavior of magneticsusceptibility and the dramatic downturn of the resistivity below T* indicate strong Cu2+3d and Ir3.75+5d orbital hybridization below T*, also supportedby an enhanced electronic specific heat coefficient at low temperature.Theoretical calculations are in good agreement with the experimentalresults and show that the electronic structure of LaCu3Ir4O12is different from that of CaCu2+3Ir4+4O12, which is alsometallic down to 0.5 K, but presents non-Fermi liquid behavior above T* ∼ 80 K and strong Cu-3d–Ir-5d orbital couplingat significantly lower temperature (T< T* ∼ 80 K). [ABSTRACT FROM AUTHOR]

Hochdruckgebiet: Polare magnetische Oxide vom LiNbO3 ‐ Typ wurden erstmals auf die A2BB′O6 ‐ Familie ausgedehnt. Bei hohem Druck synthetisierte Oxide mit der allgemeinen Summenformel Mn2+2Fe3+M5+O6 (M=Nb, Ta) nehmen eine polare Struktur ein, wie durch Elektronenbeugung und den Frequenzverdopplungseffekt gezeigt wurde, und zeigen interessante magnetische Eigenschaften. [ABSTRACT FROM AUTHOR]

The title perovskites (obtained from citrate precursors at 900 °C for 12 h) are characterized by XRD, neutron powder diffraction, and magnetic measurements. All the compounds crystallize in the monoclinic space group P21/n (Z = 4) with almost complete ordering between Ni2+ and Mn4+ cations on the octahedral perovskite sublattice. All compounds are ferrimagnetic, with a net magnetic moment different from zero and a distinct alignment of Ni and Mn spins depending on the nature of the lanthanide cation. The magnetic structures are different from that previously reported for La2NiMnO6. The magnetic ordering temperature decreases with decreasing size of the lanthanoids. [ABSTRACT FROM AUTHOR]

Pb2MReO6 (M: Co (I), Cr (II)) perovskites are prepared by hot pressing of stoichiometric amounts of PbO, Cr2O3 (CoO), Re, and ReO3 (Pt capsule in multianvil press, 1423 (I) and 1473 K (II), 8 GPa, 30 min). [ABSTRACT FROM AUTHOR]

Understanding the electric dipole switching in multiferroic materials requires deep insight of the atomic-scale local structure evolution to reveal the ferroelectric mechanism, which remains unclear and lacks a solid experimental indicator in high-pressure prepared LiNbO 3 -type polar magnets. Here, we report the discovery of Zn-ion splitting in LiNbO 3 -type Zn 2 FeNbO 6 established by multiple diffraction techniques. The coexistence of a high-temperature paraelectric-like phase in the polar Zn 2 FeNbO 6 lattice motivated us to revisit other high-pressure prepared LiNbO 3 -type A 2 BB'O 6 compounds. The A-site atomic splitting (∼1.0-1.2 Å between the split-atom pair) in B/B'-mixed Zn 2 FeTaO 6 and O/N-mixed ZnTaO 2 N is verified by both powder X-ray diffraction structural refinements and high angle annular dark field scanning transmission electron microscopy images, but is absent in single-B-site ZnSnO 3 . Theoretical calculations are in good agreement with experimental results and suggest that this kind of A-site splitting also exists in the B-site mixed Mn-analogues, Mn 2 FeMO 6 (M = Nb, Ta) and anion-mixed MnTaO 2 N, where the smaller A-site splitting (∼0.2 Å atomic displacement) is attributed to magnetic interactions and bonding between A and B cations. These findings reveal universal A-site splitting in LiNbO 3 -type structures with mixed multivalent B/B', or anionic sites, and the splitting-atomic displacement can be strongly suppressed by magnetic interactions and/or hybridization of valence bands between d electrons of the A- and B-site cations.

Perovskites (ABO 3 ) with transition metals in active B sites are considered alternative catalysts for the water oxidation to oxygen through the oxygen evolution reaction (OER) and for the oxygen reduction through the oxygen reduction reaction (ORR) back to water. We have synthesized a double perovskite (A 2 BB'O 6 ) with different cations in A, B, and B' sites, namely, (La 1.5 Sr 0.5 ) A (Ni 0.5 Mn 0.5 ) B (Ni 0.5 Ru 0.5 ) B' O 6 (LSNMR), which displays an outstanding OER/ORR bifunctional performance. The composition and structure of the oxide has been determined by powder X-ray diffraction, powder neutron diffraction, and transmission electron microscopy to be monoclinic with the space group P2 1 / n and with cationic ordering between the ions in the B and B' sites. X-ray absorption near-edge spectroscopy suggests that LSNMR presents a configuration of ∼Ni 2+ , ∼Mn 4+ , and ∼Ru 5+ . This bifunctional catalyst is endowed with high ORR and OER activities in alkaline media, with a remarkable bifunctional index value of ∼0.83 V (the difference between the potentials measured at -1 mA cm -2 for the ORR and +10 mA cm -2 for the OER). The ORR onset potential ( E onset ) of 0.94 V is among the best reported to date in alkaline media for ORR-active perovskites. The ORR mass activity of LSNMR is 1.1 A g -1 at 0.9 V and 7.3 A g -1 at 0.8 V. Furthermore, LSNMR is stable in a wide potential window down to 0.05 V. The OER potential to achieve a current density of 10 mA cm -2 is 1.66 V. Density functional theory calculations demonstrate that the high ORR/OER activity of LSNMR is related to the presence of active Mn sites for the ORR- and Ru-active sites for the OER by virtue of the high symmetry of the respective reaction steps on those sites. In addition, the material is stable to ORR cycling and also considerably stable to OER cycling.