Functional Materials Letters

Li-rich layer-structured xLi₂MnO₃ ⋅ (1 - x)LiMO₂ (M = Mn, Ni, Co, etc.) materials have attracted much attention due to their extraordinarily high reversible capacity as the cathode material in Li-ion batteries. To better understand the nature of this type of materials, this paper reviews history of development of the Li-rich cathode materials, and provides in-depth study on complicated crystal structures and reaction mechanisms during electrochemical charge/discharge cycling. Despite the fabulous capability at low rate, several drawbacks still gap this type of high-capacity cathode materials from practical applications, for instance the large irreversible capacity loss at first cycle, poor rate capability, severe voltage decay and capacity fade during electrochemical charge/discharge cycling. This review will also address mechanisms for these inferior properties and propose various possible solutions to solve above issues for future utilization of these cathode materials in commercial Li-ion batteries.

In the current work, activated carbon monoliths have been prepared by application of different phenolic hydrocarbons namely catechol and resorcinol as carbon precursors. For synthesis of carbon monolith, the precursors have been mixed with Genapol PF-10 as template and then polymerized in the presence of lysine as catalyst. Then the polymerized monolith carbonized in inert atmosphere at 700°C and activated by water steam at 550°C. It was found that resorcinol polymerization is easier than catechol and occurred at 90°C while for polymerization of catechol elevated temperature of 120°C at hydrothermal condition is necessary. The prepared activated carbon samples have been characterized by various analysis methods including scanning electron microscopy (SEM), surface area measurement, and transmission electron microscopy (TEM). The adsorptions of three different aromatic hydrocarbons by the prepared activated carbon samples have also been investigated by high performance liquid chromatography (HPLC) and UV–Vis spectroscopy. It was found that carbon monolith prepared by catechol as carbon precursor has higher adsorpability and strength in comparison with the other sample. The higher performance of carbon monolith prepared by catechol can be associated with its higher active sites in comparison with resorcinol.

A series of Sb-doped Mg₂(Si_0.4Sn_0.6)Sb_x (0 ≤ x ≤ 0.025) solid solutions were prepared by an induction melting, Melt Spinning (MS) and Spark Plasma Sintering (SPS) method, namely the non-equilibrium technique MS–SPS, using bulks of Magnesium, Silicon, Tin, and Antimony as raw materials. The non-equilibrium technique generates the unique multiscale microstructures of samples containing micronscale grains and nanoscale precipitates, the multiscale microstructures remarkably make the lattice thermal conductivities decreased, particularly for samples with the nanoscale precipitates having the size of 10–20 nm. Meanwhile, Sb-doping greatly increased the electrical performance of samples. Consequently, the Sb-doping combined with the multiscale microstructures strategy remarkably improves the overall thermoelectric (TE) performance of Sb doped samples, and a high dimensionless figure of merit (ZT) value of up to 1.25 at 723 K is obtained with Mg₂(Si_0.4Sn_0.6)Sb_0.02 sample in a relatively wide temperature range.

Al-doped ZnO (AZO) powders with flower-like microstructures were successfully synthesized through a simple and efficient hydrothermal approach, and were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy diffraction spectrum (EDS). All the samples presented high crystallinity with a hexagonal wurtzite structure. The heater gas sensors based on AZO were fabricated and investigation of gas sensing properties was conducted. The sensors showed high response values and reproducible response-recovery for 50–1800 ppm ethanol at 332°C, comparing with NH₃, SO₂, CO, and HCHO. The underlying mechanism was discussed.

Phosphors based on calcium carbonate, co-doped with various Eu³⁺ and Dy³⁺ concentrations were prepared by microwave co-precipitation method. The prepared phosphors were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), thermogravimetry and differential scanning calorimetry (TG-DSC) and photoluminescence and photoluminescence excitation (PL-PLE) spectroscopy. Results showed that Dy³⁺ and Eu³⁺ ions were uniformly introduced into the host lattice of CaCO₃ taking the place of Ca²⁺ ions. Under the excitation at 382 nm, the emission peak wavelengths were at 487 nm (⁴F_9/2 → ⁶H_15/2 of Dy³⁺), 576 nm (⁴F_9/2 → ⁶H_13/2 of Dy³⁺), and 614 nm (⁵D₀ → ⁷F₂ of Eu³⁺). The luminescent intensities and emitting colors of Eu³⁺-Dy³⁺ co-doped CaCO₃ phosphors could be controlled by UV–violet excitations wavelengths or the rare-earth ions concentrations of Eu³⁺ and Dy³⁺ in phosphors. The chromaticity coordinates and photographs of samples under UV light showed the changes of the luminescence color intuitively through the varing UV–violet excitations wavelengths or the rare-earth ions concentrations of Eu³⁺ and Dy³⁺.

ZnO/TiO₂ composite films composed of a ZnO nanoflowers overlayer and a ZnO/TiO₂ composite particulate underlayer were fabricated by a simple hydrothermal process. The as-prepared films were characterized by scanning electron microscopy, transmission electron microscopy (TEM) and diffused reflectance spectroscopy. The performance of dye-sensitized solar cells (DSCs) was investigated by photocurrent–voltage measurements, incident photon-to-current conversion efficiency (IPCE) and electrochemical impedance spectroscopy. It was found that the ZnO/TiO₂ composite film prepared with a 60 min growth time exhibited higher reflectivity than that of pure TiO₂ film due to the effective light-scattering of ZnO nanoflowers, resulting in increased J_sc. In the meantime, the open-circuit potential of the device were enhanced from 698 to 826 mV due to the formation of an energy barrier by ZnO at TiO₂/electrolyte interface, resulting in a 52% improvement in the power conversion efficiency from 4.64 to 7.06%.

Vickers hardness, phase combination, elastic modulus and cutting performance of the cubic boron nitride (cBN) based composites with different cBN weight ratios sintered at high pressure and high temperature were investigated. During high-pressure sintering, reactions occurred between cBN and Ti₃SiC₂, then new compounds, TiB₂, C_0.7N_0.3Ti, SiC and SiB₄ were formed, and no hBN phase was observed. Bulk modulus and hardness of the cBN composites decreased with increasing Ti₃SiC₂ contents in raw mixture, and the highest hardness of 35.9 GPa was achieved for 95 wt.% cBN–5 wt.% Ti₃SiC₂ composition specimen sintered at 1600°C. In addition, the present cBN-based composites exhibited good cutting performance.

Epitaxial BiFe_0.95Mn_0.05O₃ (BFMO) film with room-temperature switching properties is prepared on SrTiO₃ (STO) substrate with a SrRuO₃ (SRO) buffer layer by sol–gel method coupled with rapid thermal annealing (RTA). The remnant polarization and coercive field of SRO/BFMO/SRO capacitor, measured at 455 kV/cm, are 51.8 μC/cm² and 153.5 kV/cm, respectively. Besides the good fatigue resistance and retention characteristics, the relatively small leakage current density of the capacitor is mainly attributed to the suppression of oxygen vacancies resulting from RTA. Moreover, the SRO/BFMO/SRO capacitor satisfies the Ohmic conduction behavior at fields lower than 90 kV/cm, and the Schottky emission at fields higher than 90 kV/cm.

High-temperature shape memory alloys are promising candidates for actuator applications at elevated temperatures. Ternary nickel–titanium-based alloys either contain noble metals which are very expensive, or suffer from poor workability. Titanium–tantalum shape memory alloys represent a promising alternative if one can avoid the cyclic degradation due to the formation of the omega phase. The current study investigates the functional fatigue behavior of Ti–Ta and introduces a new concept providing for pronounced fatigue life extension.

Hexafluoroisopropanol phenyl group functionalized materials have great potential in the application of gas-sensitive materials for nerve agent detection, due to the formation of strong hydrogen-bonding interactions between the group and the analytes. In this paper, take full advantage of ultra-large specific surface area and plenty of carbon–carbon double bonds and hexafluoroisopropanol phenyl functionalized graphene was synthesized through in situ diazonium reaction between -C=C- and p-hexafluoroisopropanol aniline. The identity of the as-synthesis material was confirmed by transmission electron microscopy, Raman spectroscopy, ultraviolet visible spectroscopy, X-ray photoelectron spectroscopy and thermo gravimetric analysis. The synthesis method is simply which retained the excellent physical properties of original graphene. In addition, the novel material can be assigned as an potential candidate for gas sensitive materials towards organophosphorus nerve agent detection.

The electrical properties of yttrium doped bismuth zinc niobium oxide (BZN) pyrochlore ceramics are explored by means of temperature dependent electrical conductivity dielectric constant and capacitance spectra in the frequency range of 0–3 GHz. It is observed that the doped BZN exhibit a conductivity type conversion from intrinsic to extrinsic as the doping content increased from 0.04 to 0.06. The thermal energy bandgap of the intrinsic type is 3.45 eV. The pyrochlore is observed to exhibit a dielectric breakdown at 395 K. In addition, a negative capacitance (NC) spectrum with main resonance peak position of 23.2 MHz is detected. The NC effect is ascribed to the increased polarization and the availability of more free carriers in the device. When the NC signal amplitude is attenuated in the range of 0–20 dBm at 50 MHz and 150 MHz, wide tunability is monitored. Such characteristics of the Y-doped BZN are attractive for using them to cancel the positive parasitic capacitance of electronic circuits. The canceling of parasitic capacitance improves the high frequency performance of filter inductors and reduces the common mode noise of the resonance signal.

Barium dititanate (BaTi₂O₅) ceramics with high density and phase purity were fabricated by spark plasma sintering (SPS) from the sol–gel derived powders. The fine grained ceramics exhibited a diffuse phase transition which is qualitatively the same as the conventional defects induced relaxor behavior but different in high transition temperature and weak diffuseness. Furthermore the dielectric constant of the present BaTi₂O₅ ceramics showed an abnormal enhancement under the dc bias. The tunability can reach 58%. This can be explained by the favor of b-axis during the cooling process with the help of the dc bias.

Nickel Ferrite (NiFe₂O₄) doped with Samarium (Sm) (0.2, 0.3, 0.4, 0.5 mol.%) was prepared by the conventional solid-state reaction. The crystal structure, surface morphology, infrared spectrum of absorption, and magnetic properties of samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and vibrating sample magnetometer (VSM). XRD patterns were indexed with inverse spinel cubic phase with the space group of Fd-3m of nickel ferrite. The average grain size was about 5–10 μm. FTIR spectral study on the NiFe₂O₄ ferrite phase was recorded between 350 cm^-1 and 4000 cm^-1. Two fundamental absorption bands of the ferrites were appeared at 450 cm^-1 and 1000 cm^-1 characteristic of metal vibrations. VSM measurements show that the NiFe₂O₄ doped with Sm 0.3% has the highest value of saturation magnetization. It is also easily demagnetized due to the low value of coercivity field it has. Both NiFe₂O₄ doped with Sm 0.2 mol.% and 0.4 mol.% materials have same values of coercivity field. However, NiFe₂O₄ doped with Sm 0.4 mol.% material has the comparatively high value of saturation magnetization than NiFe₂O₄ doped with Sm 0.2%, also this material was hardly demagnetized, and has highest coercivity field.

Dy³⁺, Ho³⁺–Yb³⁺ and Er³⁺–Yb³⁺-doped Ca₁₀K(PO₄)₇ phosphors were prepared by solid-state reaction method, and their luminescence properties of near-infrared (NIR) quantum cutting (QC) were investigated for the first time. The Rietveld refinement performed for the X-ray diffractometer (XRD) data indicates the obtained samples are single-phase. From the excitation spectra, it can be seen that the energy transfers from Ho³⁺ to Yb³⁺, and from Er³⁺ to Yb³⁺ occur. The Dy³⁺, Ho³⁺–Yb³⁺ and Er³⁺–Yb³⁺ co-doped Ca₁₀K(PO₄)₇ samples all exhibit NIR emission peaks in the QC processes, and their spectral characteristics are agreement with the corresponding NIR QC mechanisms. The NIR QC properties of the as-prepared samples indicate the potential applications in modifying the solar spectrum to enhance the efficiency of silicon solar cells.

The novel 3D graphene oxide/multi-walled carbon nanotubes/ZnO nanocrystalline aggregate (GR/MWNTs/ZnO) hybrids were prepared by a spray drying method, and their adsorption and photocatalytic degradation for methyl orange (MO) were studied. Experimental results show that the synthetic GR/MWNTs/ZnO nanohybrids exhibited very strong adsorption capacity and high photocatalytic activity for MO. The maximum adsorption capacity of GR/MWNTs/ZnO sample reached 106.2 mg/g, and the photocatalytic efficiency of ZnO nanocrystallines was improved about one time by GR/MWNTs hybrids.

Using an flexible amide-type tripodal ligand N,N′,N″-tris(3-pyridyl)-1,3,5-benzenetricarboxamide (L) and 1,4-benzenedicarboxylic acid (H₂bdc), a three-dimensional copper(II) metal-organic framework (MOF) formulated as [Cu(bdc)(L)]_n has been hydrothermally synthesized and structurally characterized by IR, elemental, X-ray single-crystal diffraction and thermal analysis. The complex crystallizes in the triclinic, space group P - 1, a = 8.891(2) Å, b = 11.760(2) Å, c = 15.348(3) Å, α = 96.73(3)°, β = 105.96(3)°, γ = 106.47(3)°, V = 1446.2(5) ų, M_r = 666.10, Dc = 1.530 g/cm³, Z = 2, F(000) = 682, GOOF = 1.0560, μ(MoKα) = 0.817 mm^-1, R = 0.0366 and wR = 0.0885. The structural analyses reveal that the title compound consists of one Cu(II) atom, two halves of bdc, and one L ligand. Each Cu(II) atom is linked by two bdc ligands and three L ligands to form a three-dimensional network. In addition, the electrochemical behavior of title compound has been studied. CCDC No. 990526.