High-performance heterostructure Na0.7MnO2.05-Na0.91MnO2 as a lithium-free cathode for lithium-ion batteries.

In this investigation, a lithium-free cathode material, Na0.7MnO2.05-Na0.91MnO2, was synthesized by the solid phase method. The intercalation mechanism and partial phase transformation mechanism of NMO600 were clarified by in situ X-ray diffraction and impedance. The design of the heterostructure is favourable for improving the lithium ion storage of NMO600, which can deliver a discharge capacity of 83.12 mA h g-1 at 1 A g-1 and keep 61.71 mA h g-1 after 700 cycles.

A polar oxyhalogen-vanadate compound (C5NH13Cl)2VOCl4 with optical and two-staged dielectric switch behavior.

Polar organic-inorganic hybrid materials have been applied in ferroelectricity, as well as in devices based on nonlinear optical and piezoelectricity properties. Here, we used a rectangular pyramid structure of [VOCl4]2- to construct a polar compound (C5NH13Cl)2VOCl4 (1). Compound 1 crystallized in the monoclinic P21 space group. Coexistence of nonlinear optical switching behavior (space-group change from P21 to P21/n) and two-staged thermosensitive dielectric switching properties could be achieved under the stimulus of temperature. Our findings provide an effective approach for construction of polar materials.

Magnetodielectric Response in a Layered Mixed-Valence Ferrimagnetic Molecular Compound.

The magnetodielectric effect is closely related to multiferroic or magnetoelectric coupling; thus, it can be used to predict magnetoelectric coupling, especially in compounds with special magnetic properties. The magnetodielectric response can often be used to predict many interesting and meaningful physical coupling mechanisms. Therefore, fabricating magnetodielectric materials is an effective step toward the development of magnetoelectric materials. Herein, we synthesize the mixed-valence layered ferrimagnetic molecular compound (C6N2H14)FeIII2FeIIF8(HCOO)2 (1) and demonstrate that it exhibits both slow magnetic relaxation behavior and long-range magnetic order. This long-range order occurs because of the coexistence and competition between two typical magnetic interactions, namely, an FeIII-F-FeII superexchange and a long-distance superexchange FeII-O-C-O-FeIII-F-FeIII path in the interlayer and interchain spin frustration. Notably, this compound also demonstrates two abnormal dielectric relaxation processes: the first process is dominated by dynamic guest cations, while the other process is related to the increasing magnetic correlation. Over a wide temperature range below 170 K, the magnetodielectric effect reveals that the magnetic correlation maybe promotes electron dynamics and leads to magnetodielectric coupling. These findings pave a novel path for designing magnetodielectric molecular materials.

Thermal hysteresis induced by external pressure in a 3D Hofmann-type SCO-MOF.

Two isostructural 3D Hofmann-type frameworks, [FeII(dbdpe)MII(CN)4]·4H2O (M = Pt for 1 and Pd for 2), were synthesized based on a bis-monodentate ligand dbdpe (1,2-dibromo-1,2-di(pyridin-4-yl)ethane). Both compounds underwent similar one-step incomplete spin crossover (SCO) processes in the presence of lattice water molecules, i.e., T1/2↓ = 185 K for 1 and 187 K for 2 without any hysteresis loop, while their dehydrated products exhibited paramagnetic behaviours. The application of pressure on 1 broadened the hysteresis loop to 13-25 K and shifted the transition temperature from 185 to 298 K, whereas the SCO completeness was not well improved. Variable temperature X-ray crystallographic studies clearly confirmed the incomplete SCO behaviors, and the intermolecular hydrogen bonds might promote the cooperativity in the SCO processes.

A breakthrough in the intrinsic multiferroic temperature region in Prussian blue analogues.

Thin films of [(FeII x CrII 1-x )]1.5[CrIII(CN)6]·yH2O (x ≈ 0.30-0.35, y ≈ 1.77) (1) on FTO substrates (namely film 1) were synthesized with an electrochemical method. Investigation of the ferroelectricity of film 1 at different temperatures reveals that it exhibits ferroelectric behaviour in the temperature range from 10 K to 310 K. Study of the X-ray absorption (XAS) of the crushed film 1 and simulation of the structure of film 1 and crushed film 1 by using the Materials Studio software indicate that the vacancy defects and interactions between the film and FTO substrate make a key contribution to the ferroelectricity of film 1. Owing to the magnetic phase transition point being up to 210 K, film 1 is a multiferroic material and its magneto/electric coexistence temperature can be as high as 210 K.

LiNa4B15O25: Featuring Unprecedented B15O30 Fundamental Building Block and Deep-UV Cutoff Edge.

In the Li2O-Na2O-B2O3 system, LiNa4B15O25 has been successfully synthesized, which crystallizes in monoclinic space group C2 /c (No. 15), a = 14.153(3) Å, b = 12.122(2) Å, c = 12.719(2) Å, ß = 105.237(13)°, and Z = 4. The isolated LiO5 polyhedra and the Na4O18 tetramers are located in the void space of the 3D ∞[B15O25] network of LiNa4B15O25. The symmetry of B15O30 is a new fundamental building block, which has never been reported before. Moreover, the whole framework can be defined as a new topology based on the TOPOS database. Interestingly, for the crystal structure LiB3O5, as 4/5 Li+ ions are substituted by the Na+ ions, a new compound LiNa4B15O25 has been successfully prepared. The structural comparison between the structures of LiB3O5 and LiNa4B15O25 and the changes caused by the cation substitution are discussed in this paper.

Active performance of tetrahedral groups to SHG response: theoretical interpretations of Ge/Si-containing borate crystals.

As potential candidates for deep-UV nonlinear optical (NLO) crystals, borosilicates and borogermanates, which contain NLO-active groups such as B-O, Si-O and Ge-O, have fascinated many scientists. The crystal structures, electronic structures and optical properties of seven borates in different B/R (R = Si, Ge) ratios have been studied using DFT methods. Through the SHG-density, we find that besides the recognized contribution of the π-conjugation configuration of BO3 to second harmonic generation (SHG), the tetrahedra have a non-negligible influence. This is because the non-bonding p orbitals of the bridging oxygen in the tetrahedra are observably closer to the Fermi level than those in BO3, which is observed in the PDOS of Rb4Ge3B6O17 and RbGeB3O7. This conclusion would be very meaningful in the understanding of the relationship between the crystal structure and nonlinear optical properties.

Versatile Coordination Mode of LiNaB8O13 and α- and ß-LiKB8O13 via the Flexible Assembly of Four-Connected B5O10 and B3O7 Groups.

Three new alkali-metal mixed borates, LiNaB8O13, α-LiKB8O13, and ß-LiKB8O13, containing a (3)∞[B8O13] three-dimensional network have been successfully synthesized. Their fundamental building block is [B8O16](8-) formed by the vertex-sharing [B5O10](5-) and [B3O7](5-) groups, which are topologically identical when they are considered as four-connected nodes. The viewpoints give us a feasible way to investigate the versatile structure assembly of borates with a complex network.