Effect of the Transition Metal Ions on the Single-Molecule Magnet Properties in a Family of Air-Stable 3d-4f Ion-Pair Compounds with Pentagonal Bipyramidal Ln(III) Ions.

Single-molecule magnets (SMMs) are expected to be promising candidates for the applications of high-density information storage materials and quantum information processing. Lanthanide SMMs have attracted considerable interest in recent years due to their excellent performance. It has always been interesting but not straightforward to study the relaxation and blocking mechanisms by embedding 3d ions into 4f SMMs. Here we report a family of air-stable 3d-4f ion-pair compounds, YFe (1), DyCr (2), DyFe (3), DyCo (4), and Dy0.04Y0.96Fe (5), composed of pentagonal bipyramidal (D5h) LnIII cations and transition metallocyanate anions. The ion-pair nature makes the dipole-dipole interactions almost the only component of the magnetic interactions that can be clarified and analytically resolved under proper approximation. Therefore, this family provides an intuitive opportunity to investigate the effects of 3d-4f and 4f-4f magnetic interactions on the behavior of site-resolved 4f SMMs. Dynamic magnetic measurements of 1 under a 4 kOe external field reveal slow magnetic relaxation originating from the isolated [FeIII]LS (S = 1/2) ions. Under zero dc field, compounds 2-5 show similar magnetic relaxation processes coming from the separated pentagonal bipyramidal (D5h) DyIII ions with high Orbach barriers of 592(5), 596(4), 595(3), and 606(4) K, respectively. Comparatively, both compounds 3 and 5 exhibit two distinct relaxation processes, respectively from the [FeIII]LS and DyIII [Ueff = 596(4) K for 3 and 610(7) K for 5] ions, under a 4 kOe dc field. The dipolar interactions between the neighboring TMIII (TM = transition metal, CrIII or [FeIII]LS) and DyIII ions were revealed to have little effect on the thermal relaxation in compounds 2, 3, and 5, or the coexistence of the two separate relaxation processes in compounds 3 and 5 under a 4 kOe dc field, but they significantly affect the quantum tunneling of magnetization and the magnetic hysteresis behavior of 2 and 3 at low temperatures compared to those of 4.

Synthesis, Doping and Electrochemical Properties of Zn3V3O8.

The Zn3V3O8 was synthesized by solvothermal method combined with heat treatment using Zn(NO3)3 · 6H2O and NH4VO3 as raw materials. The Zn3V3O8 was doped by Co2+ to form Zn2.88Co0.12V3O8. The samples were characterized by X-ray diffraction and scanning electron microscopy techniques. Electrochemical tests showed that the initial discharge specific capacity for Zn2.88Co0.12V3O8 was 640.4 mAh·g-1 when the current density was 100 mA·g-1, which was higher than that of pure Zn3V3O8 (563.5 mAh · g-1). After 80 cycles, the discharge specific capacity of Zn2.88Co0.12V3O8 could maintain at 652.2 mAh · g-1, which was higher than that of pure Zn3V3O8 (566.8 mAh·g-1) under same condition. The Zn2.88Co0.12V3O8 owned better rate performances than those of pure Zn3V3O8 also. The related modification mechanisms were discussed in this paper.

Synthesis and Electrochemical Properties of CuC2O4·xH2O and CuC2O4·xH2O/Carbon Nanotubes (CNTs) Anodes for Lithium-Ion Batteries.

Pure CuC2O4·xH2O and CuC2O4·xH2O/carbon nanotubes (CNTs) composites are synthesized by a low-temperature hydrothermal process. The structure and morphology of the products are analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TG) and Raman spectrum. The results demonstrate that the as-prepared CuC2O4·xH2O takes on a microsphere-like morphology, all CuC2O4·xH2O/CNTs nanocomposites are constructed by the intertwining of tabular CuC2O4·xH2O nanoparticles (NPs) and CNTs to form a tanglesome net. When evaluated as an anode materials for lithium ion batteries (LIBs), all CuC2O4·xH2O/CNTs electrodes possess higher reversible discharge capacities (more than 1000 mAh g-1) than the pure CuC2O4·xH2O, up to 200th cycle at a current density of 100 mA g-1. The results illustrate that the addition of CNTs can enhance the electrochemical performance of CuC2O4·xH2O. Overall, CuC2O4·xH2O/CNTs composite can be a promising candidate used as a promising anode for LIBs.

In-situ one-step hydrothermal synthesis of a lead germanate-graphene composite as a novel anode material for lithium-ion batteries.

Lead germanate-graphene nanosheets (PbGeO3-GNS) composites have been prepared by an efficient one-step, in-situ hydrothermal method and were used as anode materials for Li-ion batteries (LIBs). The PbGeO3 nanowires, around 100-200 nm in diameter, are highly encapsulated in a graphene matrix. The lithiation and de-lithiation reaction mechanisms of the PbGeO3 anode during the charge-discharge processes have been investigated by X-ray diffraction and electrochemical characterization. Compared with pure PbGeO3 anode, dramatic improvements in the electrochemical performance of the composite anodes have been obtained. In the voltage window of 0.01-1.50 V, the composite anode with 20 wt.% GNS delivers a discharge capacity of 607 mAh g(-1) at 100 mA g(-1) after 50 cycles. Even at a high current density of 1600 mA g(-1), a capacity of 406 mAh g(-1) can be achieved. Therefore, the PbGeO3-GNS composite can be considered as a potential anode material for lithium ion batteries.

[Research on IR spectra of Li-Mn spinel].

The infrared spectra of Li-Mn-spinel were studied in this paper. As the structure of Li-Mn-spinel was classified as Fd3m space group, the lithium ions (Li(I)) occupy tetrahedral sites (8a sites) and manganese ions (Mn(IV) or Mn(III)) occupy octahedral sites (16d sites). The internal relationship between vibration modes and infrared activity was discussed based on the knowledge of group theory. The experimental IR spectra of Li-Mn-spinel were presented also. By theoretical analysis, we concluded that the bands at 618.6 and 501.5 cm-1 resulted from anti-symmetric stretching vibration of Mn(IV)-O and Mn (III)-O in Li-Mn-spinel crystal (Mn(IV)O6 and Mn(III)O6 octahedron), respectively, the weak band at 1,124 cm-1 resulted from anti-symmetric stretching vibration of Li-O in the spinel (LiO4 tetrahedron), and other possible bands at wave number lower than 400 cm-1 were not detected in the range from 400 to 4,000 cm-1. The reliability of conclusions was proved by IR spectra of both the Li-Mn-spinel and doped Li-Mn-spinel.