Large Magnetization and Frustration Switching of Magnetoresistance in the Double‐Perovskite Ferrimagnet Mn2FeReO6

Ferrimagnetic A₂BB′O₆ double perovskites, such as Sr₂FeMoO₆, are important spin‐polarized conductors. Introducing transition metals at the A‐sites offers new possibilities to increase magnetization and tune magnetoresistance. Herein we report a ferrimagnetic double perovskite, Mn₂FeReO₆, synthesized at high pressure which has a high Curie temperature of 520 K and magnetizations of up to 5.0 μ_B which greatly exceed those for other double perovskite ferrimagnets. A novel switching transition is discovered at 75 K where magnetoresistance changes from conventional negative tunneling behavior to large positive values, up to 265 % at 7 T and 20 K. Neutron diffraction shows that the switch is driven by magnetic frustration from antiferromagnetic Mn²⁺ spin ordering which cants Fe³⁺ and Re⁵⁺ spins and reduces spin‐polarization. Ferrimagnetic double perovskites based on A‐site Mn²⁺ thus offer new opportunities to enhance magnetization and control magnetoresistance in spintronic materials.     

High‐Pressure Synthesis of Cd(NH3)2[B3O5(NH3)]2: Pioneering the Way to the Substance Class of Ammine Borates

To date, the access to the substance class of borates containing nitrogen, for example, nitridoborates, oxonitridoborates, or amine borates, was an extreme effort owing to the difficult starting materials and reaction conditions. Although a number of compounds containing boron and nitrogen are known, no adduct of ammonia to an inorganic borate has been observed so far. A new synthetic approach starting from the simple educts CdO, B₂O₃, and aqueous ammonia under conditions of 4.7 GPa and 800 °C led to the synthesis of Cd(NH₃)₂[B₃O₅(NH₃)]₂ as the first ammine borate. We thoroughly characterized this compound on the basis of low‐temperature single‐crystal and powder X‐ray diffraction data, IR and Raman spectroscopy, and by quantum theoretical calculations. This contribution shows that the adduct of NH₃ to the BO₃ group of a complex B–O network can be stabilized, opening up a fundamentally new synthetic route to nitrogen‐containing borates.     

Oxonium Ions Substituting Cesium Ions in the Structure of the New High‐Pressure Borate HP‐Cs1−x(H3O)xB3O5 (x=0.5–0.7)

The new high‐pressure borate HP‐Cs_1?x(H₃O)_xB₃O₅ (x=0.5–0.7) was synthesized under high‐pressure/high‐temperature conditions of 6 GPa/900 °C in a Walker‐type multianvil apparatus. The compound crystallizes in the monoclinic space group C2/c (Z=8) with the parameters a=1000.6(2), b=887.8(2), c=926.3(2) pm, β=103.1(1)°, V=0.8016(3) nm³, R1=0.0452, and wR2=0.0721 (all data). The boron–oxygen network is analogous to those of the compounds HP‐MB₃O₅, (M=K, Rb) and exhibits all three structural motifs of borates—BO₃ groups, corner‐sharing BO₄ tetrahedra, and edge‐sharing BO₄ tetrahedra—at the same time. Channels inside the boron–oxygen framework contain the cesium and oxonium ions, which are disordered on a specific site. Estimating the amount of hydrogen by solid‐state NMR spectroscopy and X‐ray diffraction led to the composition HP‐Cs_1?x(H₃O)_xB₃O₅ (x=0.5–0.7), which implies a nonzero phase width.     

Li3PO4‐Coated LiNi0.5Mn1.5O4: A Stable High‐Voltage Cathode Material for Lithium‐Ion Batteries

LiNi_0.5Mn_1.5O₄ is regarded as a promising cathode material to increase the energy density of lithium‐ion batteries due to the high discharge voltage (ca. 4.7 V). However, the interface between the LiNi_0.5Mn_1.5O₄ cathode and the electrolyte is a great concern because of the decomposition of the electrolyte on the cathode surface at high operational potentials. To build a stable and functional protecting layer of Li₃PO₄ on LiNi_0.5Mn_1.5O₄ to avoid direct contact between the active materials and the electrolyte is the emphasis of this study. Li₃PO₄‐coated LiNi_0.5Mn_1.5O₄ is prepared by a solid‐state reaction and noncoated LiNi_0.5Mn_1.5O₄ is prepared by the same method as a control. The materials are fully characterized by XRD, FT‐IR, and high‐resolution TEM. TEM shows that the Li₃PO₄ layer (<6 nm) is successfully coated on the LiNi_0.5Mn_1.5O₄ primary particles. XRD and FT‐IR reveal that the synthesized Li₃PO₄‐coated LiNi_0.5Mn_1.5O₄ has a cubic spinel structure with a space group of Fd$\bar 3$ m, whereas noncoated LiNi_0.5Mn_1.5O₄ shows a cubic spinel structure with a space group of P4₃32. The electrochemical performance of the prepared materials is characterized in half and full cells. Li₃PO₄‐coated LiNi_0.5Mn_1.5O₄ shows dramatically enhanced cycling performance compared with noncoated LiNi_0.5Mn_1.5O₄.     

A High‐Pressure Polymorph of Phosphorus Nitride Imide

Phosphorus nitride imide, PN(NH), is of great scientific importance because it is isosteric with silica (SiO₂). Accordingly, a varied structural diversity could be expected. However, only one polymorph of PN(NH) has been reported thus far. Herein, we report on the synthesis and structural investigation of the first high‐pressure polymorph of phosphorus nitride imide, β‐PN(NH); the compound has been synthesized using the multianvil technique. By adding catalytic amounts of NH₄Cl as a mineralizer, it became possible to grow single crystals of β‐PN(NH), which allowed the first complete structural elucidation of a highly condensed phosphorus nitride from single‐crystal X‐ray diffraction data. The structure was confirmed by FTIR and ³¹P and ¹H solid‐state NMR spectroscopy. We are confident that high‐pressure/high‐temperature reactions could lead to new polymorphs of PN(NH) containing five‐fold‐ or even six‐fold‐coordinated phosphorus atoms and thus rivalling or even surpassing the structural variety of SiO₂.     

Time‐Resolved Phase Transitions of the Nanocrystalline Cubic to Submicron Monoclinic Phase in Mn2O3‐ZrO2

The nanocrystalline cubic phase of zirconia was found to be thermally stabilized by the addition of 3 to 40 mol % manganese. The nanocrystalline cubic, tetragonal and monoclinic phases of zirconia stabilized with manganese (III)oxide (Mn‐Stabilized Zirconia) were prepared by thermal decomposition of carbonate and hydroxide precursors. Both the crystallization and isothermal phase transitions associated with Mn‐SZ were studied using high temperature x‐ray diffraction and x‐ray diffraction of quenched samples. Cubic Mn‐SZ initially crystallized and progressively transformed to tetragonal, and monoclinic structures above 700°C. The nanocrystalline cubic Mn‐SZ containing 25 mol % Mn was found to have the greatest thermal stability, retaining its cubic form at temperatures as high as 800°C for periods up to 25 hours. Higher than 40 mol %, cubic Mn₂O₃ was found to coexist with cubic Mn‐SZ. The crystallite sizes observed for the cubic, tetragonal and monoclinic Mn‐SZ phases ranged from 50 to 137, 130 to 220, and 195 to 450 Å respectively, indicating, for ZrO₂, that particle size was a primary factor in determining its polymorphs. The classical Avrami equation for nucleation and growth was applied to the observed phase transformations.     

A High‐Pressure Polymorph of Phosphorus Oxonitride with the Coesite Structure

The chemical and physical properties of phosphorus oxonitride (PON) closely resemble those of silica, to which it is isosteric. A new high‐pressure phase of PON is reported herein. This polymorph, synthesized by using the multianvil technique, crystallizes in the coesite structure. This represents the first occurrence of this very dense network structure outside of SiO₂. Phase‐pure coesite PON (coe‐PON) can be synthesized in bulk at pressures above 15 GPa. This compound was thoroughly characterized by means of powder X‐ray diffraction, DFT calculations, and FTIR and MAS NMR spectroscopy, as well as temperature‐dependent diffraction. These results represent a major step towards the exploration of the phase diagram of PON at very high pressures and the possibly synthesis of a stishovite‐type PON containing hexacoordinate phosphorus.     

Au/Mn2O3/Al2O3催化剂的制备及其deNOx活性

由于燃煤烟气、汽车尾气的过度排放 ,大气中ＮＯｘ(其中ＮＯ占 90 %以上 )浓度已呈上升趋势。ＮＯ在阳光作用下 ,易形成光化学烟雾 ,危害人体的呼吸系统。ＮＯ还是破坏大气臭氧层和形成酸雨的前驱气体之一 ,破坏生态环境。催化分解和催化还原法是消除ＮＯ(ｄｅＮＯｘ)的主要方法。但由于实际环境中ＮＯ往往与某一种或几种还原性气体 (如ＣＯ、低碳烃 )共存 ,所以催化还原法是人们公认的有应用前景的ｄｅＮＯｘ 方法[1 ] 。近十几年来 ,国内外研究较多的ｄｅＮＯｘ 催化剂是Ｃｕ ＺＳＭ 5 ,其催化活性除受原料气中氧含量的影响外 ,很大程度上…     

Ba3V2S4O3: A Mott Insulating Frustrated Quasi‐One‐Dimensional S=1 Magnet

Through a solid‐state reaction, a practically phase pure powder of Ba₃V₂S₄O₃ was obtained. The crystal structure was confirmed by X‐ray single‐crystal and synchrotron X‐ray powder diffraction (P6₃, a=10.1620(2), c=5.93212(1) Å). X‐ray absorption spectroscopy, in conjunction with multiplet calculations, clearly describes the vanadium in charge‐disproportionated V^IIIS₆ and V^VSO₃ coordinations. The compound is shown to be a strongly correlated Mott insulator, which contradicts previous predictions. Magnetic and specific heat measurements suggest dominant antiferromagnetic spin interactions concomitant with a weak residual ferromagnetic component, and that intrinsic geometric frustration prevents long‐range order from evolving.     

Mn2O3微纳米粉体的配合物热解制备与电化学性质（英文）

利用液相扩散法制备了异烟酸锰超分子配合物,通过将其在空气中高温煅烧制备了Mn2O3微纳米粉体。利用FTIR、TG-DTA、XRD、TEM和FESEM对产物进行了表征。电化学测试表明,Mn2O3微纳米粉体在0.5 mol.L-1Na2SO4电解液中表现出良好的电化学电容特性,在电流密度为0.5 A.g-1时其单电极比容量可达到88 F.g-1,循环3 000次后容量保持率可达到80%。     

Temperature‐Induced Intersite Charge Transfer Involving Cr ions in A‐Site‐Ordered Perovskites ACu3Cr4O12 (A=La and Y)

Changes in the valence state of transition‐metal ions in oxides drastically modify the chemical and physical properties of the compounds. Intersite charge transfer (ISCT), which involves simultaneous changes in the valence states of two valence‐variable transition‐metal cations at different crystallographic sites, further expands opportunities to show multifunctional properties. To explore new ISCT materials, we focus on A‐site‐ordered perovskite‐structure oxides with the chemical formula AA′₃B₄O₁₂, which contain different transition‐metal cations at the square‐planar A′ and octahedral B sites. We have obtained new A‐site‐ordered perovskites LaCu₃Cr₄O₁₂ and YCu₃Cr₄O₁₂ by synthesis under high‐pressure and high‐temperature conditions and found that they showed temperature‐induced ISCT between A′‐site Cu and B‐site Cr ions. The compounds are the first examples of those, in which Cr ions are involved in temperature‐induced ISCT. In contrast to the previously reported ISCT compounds, LaCu₃Cr₄O₁₂ and YCu₃Cr₄O₁₂ showed positive‐thermal‐expansion‐like volume changes at the ISCT transition.     

Y2O3包覆LiCo1/3Ni1/3Mn1/3O2的电化学性能

通过在硝酸钇水溶液浸渍并焙烧的简单工艺,在LiCo1/3Ni1/3Mn1/3O2材料表面包覆了一层Y2O3.采用X射线衍射(XRD),扫描电子显微镜(SEM),透射电子显微镜(TEM),循环伏安(CV)和恒流充放电对包覆和未包覆的LiCo1/3Ni1/3Mn1/3O2进行了测试分析.结果表明,Y2O3包覆并没有改变LiCO1/3Ni1/3Mn1/3O2的晶体结构,只存在于LiCo1/3Ni1/3Mn1/3O2的表面;与未包覆的材料相比,Y2O3包覆后的材料在高电位下具有更好的容量保持率和放电容量.CV测试表明,包覆层的存在有效抑制了材料层状结构的转变及电极与电解液的负反应.