Functional Materials Letters

Due to various and indefinite Li-ion distributions within the cuboctahedron surrounded by eight TiO₆ and local subtle distortions, perovskite-type solid electrolyte Li${}_{3x}$La${}_{2∕3-x}$TiO₃ (LLTO) is suitable to be used as a model system for studying the structure–conductivity relationship. This review is focused on structural characteristics, Li-ion diffusion behavior and conductivity in LLTO. Li-ion concentration, cooling rate of heat treatment and heating temperature are shown to be three main factors influencing the space group structure of LLTO, involving the distributions of Li, La ions and vacancies as well as the distortion of TiO₆ octahedron. In rhombohedral and some orthorhombic phases, Li ions partially occupy O₄ windows of cuboctahedrons, whose diffusion could be described by the bond percolation model, whereas in other phases with Li ions inside the cuboctahedrons, the site percolation model is applicable to Li-ion conduction. Li-ion conductivity versus temperature curve exhibits non-Arrhenius behavior, which is divided into three sections with different activation energies, although its first-derivative is continuous. The activation energy is correlated closely with the tilting angle of TiO₆ octahedron, both of which decrease with the increase of temperature. Experimental studies and theoretical results are discussed in parallel to provide insight into the detailed structure-conductivity relationship.

Continuous development of liquid/solid interface towards the liquid side promotes crystal growth under the chemical reaction among crystal constituents. Here, factors that determine inorganic functional materials are analyzed by establishing the chemical reaction equations at liquid/solid interface. The linear growth velocity along the [uvw] direction is directly determined by the chemical bonds formed in chemical reaction at the growing interface. In the present chemical bonding growth model, both thermodynamic and kinetic controls are integrated, which can also be classified in particular materials growth system. Taking Cu₂O as an example, we demonstrate that the critical control factor is the bonding mode in linking Cu₂O growth units controlled by chemical reaction, and various bonding modes promote the polymorph growth of inorganic functional materials.

We have previously described the enhancement of piezoelectricity in low crystallinity Bi${}_{12}$TiO${}_{20}$–BaTiO₃ (BTO-BT) nanocomposites. This poses a question regarding the effect of the crystallinity on piezoelectricity. Here, the variation of crystallinity and structure that was developed along the temperature gradient was confirmed. The magnitude of the piezoelectric constant was found to have great relationship with the crystallinity and distortion of BiO₅ polyhedra of amorphous Bi${}_{12}$TiO${}_{20}$. The highest piezoelectric constant of 13pC/N was obtained together with the lowest crystallinity and highest degree of distortion of BiO₅ polyhedra. These results highlight the key role of the amorphous phase and further confirm the importance of distortion of BiO₅ polyhedra in influencing the piezoelectricity. In this view, one may also expect that macroscopic polarity could be improved by increasing the amorphous content and the degree distortion of the BiO₅ bonding units in the system.

The effect of La${}_{0.7}$Sr${}_{0.3}$MnO${}_{3-\delta }$ (LSM) coating on SS446 steel on air oxidation at 800${}^{\circ }$C was investigated by transmission electron microscopy. Dense and crack free thin LSM films were prepared by electrostatic spray deposition. The microstructural characterization was carried out on coated and uncoated interconnectors. A thin chromia scale at the alloy interface along with two spinel phases were observed after long term oxidation in both cases. Specimens exhibit, in addition, an SiO₂ layer at the interface with steel due to the high content of Si in the steel. Significant changes in the thickness, morphology and composition occurred in the reaction layer for the LSM coated steel. These effects are explained on the basis of changes in the diffusive fluxes during exposure to the oxidation treatment. The implications of these effects for the degradation mechanism of LSM-based interconnects are discussed.

In this paper, the suitability of aqueous KOH and H₂SO₄ electrolytes in terms of ionic size, mobility, conductivity and energy of electrolyte ions with the porosity of activated carbon electrodes are demonstrated. These parameters of ions (K${}^{+}$, OH${}^{-}$, H${}^{+}$, SO${}_4^{2-}$) are found to affect the overall performances of supercapacitor cells as observed from the results of EIS, CV and GCD studies. The cell using H₂SO₄ electrolyte exhibits better performance with relatively low value of charge transfer resistance (0.57$\mathrm{\Omega }$), overall cell resistance, 19$\mathrm{\Omega }$ (at 10mHz) and high value of specific capacitance 547F g${}^{-1}$ (at 1mV s${}^{-1}$), specific energy 10W h kg${}^{-1}$ (at 0.5A g${}^{-1}$) and specific power, 490W kg${}^{-1}$. These results show that aqueous acid electrolyte is more compatible with carbon electrodes which could be due to the higher ionic energies of H${}^{+}$ and SO${}_4^{2-}$ ions.

This paper presents, the studies of the influence of (radio frequency) RF power on the size distribution and visible photoluminescence (PL) of SiN_x thin film deposited at 300${}^{\circ }$C of substrate temperature by plasma enhanced chemical vapor deposition. RF power was varied (5–50W), and its aftereffect on the optical properties of thin films was investigated. By increasing the RF power between 5W and 25W, main PL peak showed a red shift with an increase in PL intensity, which is associated with an increase in the silicon nanocrystals size and density, respectively. Results obtained were confirmed with High-resolution transmission electron microscopy micrographs and from the statistical calculations. By attaining a precise RF power value, stable silicon nitride thin film with suitable optical properties can be achieved for the potential fabrication of optoelectronic devices.

An easy recyclable and interesting Ag₃PO₄@Pt@TiO₂ (APTP) three-phase heterocrystal chains were self-assembled by the cohesive action and chemical construction of polyvinylpyrrolidone (PVP). We found that a new electron–hole transmission path has been built via the rematch of the band structure of Ag₃PO₄, Pt and TiO₂ which extends the light absorption and promoted the electron–hole separation to treat the antibiotic residues in the water. Based on the thorough investigations, a new catalytic material was provided for antibiotics degradation. The catalytic activity of APTP toward the degradation of tetracycline solution was enhanced by 166.67% and the stability increased remarkably compared with pure Ag₃PO₄ through the integration of different functional components.

Micro-sized K₂SiF₆:Mn${}^{4+}$ red phosphor was prepared by a simple method. Oleic acid (OA) was used as dispersant and reductant. In a fixed condition of the mole ratio of SiO₂/KMnO₄, the effects of the volume of OA on the morphology and luminescence properties were studied. X-ray diffraction (XRD) was used to characterize the phase. Scanning electron microscopy (SEM) and luminescence spectra were carried out to identify the morphology and the luminescence properties, respectively. The results show that the dispersive particles of K₂SiF₆:Mn${}^{4+}$ red phosphor $\sim$ 3$\mu$m larger was obtained, which is suitable for industrial applications.

ZnO nanorods (ZnO NRs) as electron transport layer (ETL) in organometal halide perovskite solar cells (PSCs) had been prepared because of ZnO exhibiting excellent electron mobility and light transmission performance. The ZnO NRs were modified with a simple solvothermal method using aluminum chloride (AlCl₃) and ammonia (NH${}_3\cdot$H₂O) as precursor solution, the primary advantage of this approach was low temperature, simple process. The concentration of the precursor solution was further investigated, and a power conversion efficiency (PCE) of 12.1% was achieved.

We report a facile easy method to deposit anatase titania (TiO${}_2)$ on cellulose paper. The anatase TiO₂/cellulose paper (ATCP) was characterized by scanning electron microscopy, transmission electron microscope, energy dispersive X-ray spectrometer, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis. This hybrid paper with the anatase TiO₂ content of around 13.86wt.% can serve as an eco-friendly flexible photocatalyst, which can rapidly degrade blue indigo carmine dye into a colorless solution within 30min under UV radiation. Moreover, compared to commercially available TiO₂ P25 and anatase TiO₂ powder, a faster decomposition rate of indigo carmine dye was acquired when using ATCP. These results suggest that this hybrid paper might be useful in the treatment of organic dye wastewater.

“Multi-layer” walled TiO₂ nanotube array has been prepared by anodization with post-treatment of ethanol. Two post-treatment methods, which were ethanol and water treatment respectively, exerted a marked and different effect on the structure of nanotube. With ethanol immersion, the “multi-layer” walled nanotube can be obtained, while water treatment cannot produce the “multi-layer” walled structure. The main reason could be the uptake of carbon and fluoride during anodization process. Compared with “single-layer” walled TiO₂ nanotube, “multi-layer” walled TiO₂ nanotube demonstrated higher photocatalytic activity.

BaAl₂O₄:Eu²⁺, Dy³⁺ phosphors with a good long lasting property can be easily obtained via a solid state reaction assisted with Li₂CO₃. The influence of Li₂CO₃ quantity on the lattice structure of BaAl₂O₄:Eu²⁺, Dy³⁺ phosphors, their photoluminescence (PL) property, and decaying process was studied by XRD, PL, and afterglow decay measurement, respectively. The results show that incorporating Li₂CO₃ in preparing process would obviously affect their lattice structure, accompanied by the variation of their luminescent property. With the increase of Li₂CO₃, their fluorescence property would gradually increase, at $m=0.04$ (${Ba}_{0.96}{Al}_2{O}_4:{\mathrm{\text{Eu}}}_{0.01}^{2+},{\mathrm{\text{Dy}}}_{0.03}^{3+}\cdot m{\mathrm{\text{Li}}}_2{\mathrm{\text{CO}}}_3)$ reach their maximum emission intensity, and then decrease; but their phosphorescence property would continue to strengthen whether in brightness and decaying time up to $m=0.07$, and then decrease.

Silicon (Si) nanowires were synthesized by direct current arc plasma jet chemical vapor deposition. It was found that growth temperature and growth time played important roles in the morphologies of the Si nanowires. The possible formation mechanism of Si nanowire was also proposed according to the corresponding results. In addition, the Ni particles are dispersed on the Si substrate with the help of alkaline etching, which enables the lateral growth of Si nanowires on a Si substrate. This offers a simple and practical way of synthesizing and positioning the Si nanowires on a substrate.

Fe₂(MoO₄)₃ nanoplates were prepared via a simple hydrothermal process. The average crystalline size of these nanoplates is 85.8nm. The sensor based on Fe₂(MoO₄)₃ shows a high gas sensing performance to xylene. The response of Fe₂(MoO₄)₃ sensor is 25.9–100ppm xylene at optimum operating temperature of 340${}^{\circ }$C. The response and recovery times to 100ppm xylene are 4 and 10s, respectively. Furthermore, the Fe₂(MoO₄)₃ sensor exhibits remarkable selectivity detection of xylene gas with negligible responses to toluene and benzene. Therefore, the Fe₂(MoO₄)₃ is a promising material for the detection of xylene gas sensors.

Beryllium (Be)-decorated graphene with 585 double carbon vacancy defect and nitrogen-doped porphyrin defect are investigated for hydrogen storage applications using the first principle calculation based on density functional theory. It is found that the Be atom disperses well in the defective sites of graphene and prevents clustering. For the case of Be-decorated 585 double vacancy graphene, only two H₂ molecules are adsorbed via Kubas interaction with the stretched H–H bond length of 0.8 Å. In Be-decorated porphyrin defect graphene system, four H₂ molecules are molecularly chemisorbed with the H–H bond length of 0.77 Å. The chemisorptions are due to the hybridization between Be-p orbital and the H-$\sigma$ orbital. The average binding energy of H₂ molecule is found to be 0.43eV/H₂ which lies within the required range that can permit recycling of H₂ molecules under ambient conditions.

Nano-crystalline Zinc oxide (ZnO) thin films on glass substrates have been fabricated by sol–gel method for different aging times. The thermal curve of the dried gel was examined and it was found that evaporation of solvent and the decomposition of the organics have completed before 250${}^{\circ }$C. X-ray diffraction patterns and Atomic Force Microscope images of samples only have a small difference of microstructure. The transmittance spectra revealed high transmittance in visible region. The optical band gap of the samples remined stable (3.28eV). Also, the Urbach energy was calculated to explain the defect concentration. The Photoluminescence spectra in ultraviolet and visible regions were studied, and the decreased intensity of peaks at 387nm and the increased emissions in visible range were found. The results showed that excessive aging time can cause degeneration of optical properties of thin films.

Core–shell Si/Cu nanocomposites were synthesized via a flexible self-limiting surface reaction without extra reductant for the first time. The nano Si was uniformly coated with Cu nanoparticles with a diameter of 5–10nm, which can enhance the electronic conductivity of the nanocomposites and buffer the huge volume change during charge/discharge owing to its high ductility. Benefited from the unique structure, the Si/Cu nanocomposites exhibited a good electrochemical performance as anodes for lithium ion batteries, which exhibited a capacity retention of 656mAh/g after 50 cycles and a coulombic efficiency of more than 99%.

The aging degradation behavior of Fe-doped Lead zirconate titanate (PZT) subjected to different heat-treated temperatures was investigated over 1000h. The aging degradation in the piezoelectric properties of PZT was indicated by the decrease in piezoelectric charge coefficient, electric field-induced strain and remanent polarization. It was found that the aging degradation became more pronounced at temperature above 50% of the PZT’s Curie temperature. A mathematical model based on the linear logarithmic stretched exponential function was applied to explain the aging behavior. A qualitative aging model based on polar macrodomain switchability was proposed.

A facile and green synthetic method for the synthesis of a Ln${}^{3+}$(Eu, Tb)-doped SrMoO₄ (SMO) microcrystals were developed using an environment-friendly low temperature hydrothermal method assisting with phenol formaldehyde resin (PFr). The microcrystals show narrow distribution and uniform particle size, and strong red and green emissions from Eu${}^{3+}$ and Tb${}^{3+}$ ions, and it is selectively quenched upon addition Fe${}^{3+}$ ions, thus making the microcrystals as a potential Fe${}^{3+}$ ions sensing material, and the detection limit is nearly micromole level.

A facile approach was developed to synthesize novel Roe-like TiO₂ hollow nanospheres via a template-assisted self-assembly process. These TiO₂ nanospheres possessing mesoporous cavity manifest significantly improved photocatalytic activity owing to the synergistic effects of increased charge separation, more efficient use of the light and specific surface area.

Silver-based nanomaterials that exhibit antibacterial character are intensively studied as they represent promising weapon against multi-drug resistant bacteria. Equally important class of materials represent coatings that have highly water repellent nature. Such materials may be used for fabrication of anti-fogging or self-cleaning surfaces. The aim of this study is to combine both of these valuable material characteristics. Antibacterial and highly hydrophobic Ag/C:F nanocomposite films were fabricated by means of gas aggregation source of Ag nanoparticles and sputter deposition of C:F matrix. The nanocomposite coatings had three-layer structure C:F base layer/Ag nanoparticles/C:F top layer. It is shown that the increasing number of Ag nanoparticles in produced coatings leads not only in enhancement of their antibacterial activity, but also causes substantial increase of their hydrophobicity. Under optimized conditions, the coatings are super-hydrophobic with water contact angle equal to 165${}^{\circ }$ and are capable to induce 6-log reduction of bacteria presented in solution within 4h.

Three-dimensionally ordered macroporous (3DOM) CuO is prepared by colloidal crystal templated method. The obtained 3DOM structure with about 230nm pore diameter is composed of small CuO windows. The special structured CuO is used as a catalyst for thermal decomposition of ammonium perchlorate (AP) and its catalytic activity is measured by simultaneous thermogravimetry-differential scanning calorimetry (TG-DSC) techniques. Test results show that thermal decomposition performance is significantly improved after adding 2wt.% 3DOM CuO.

Using synthesized sol–gel nanoimprint resist, large-area, ordered SiO₂ cylindrical and stripe photonic nanostructures with constant aspect ratio have been fabricated by a single-step soft stamp hot embossing nanoimprint. Different from the traditional hot embossing nanoimprint technique, in our imprint process, the external force applied to the soft stamp is provided just by using our hand. Since the stress can be well released, the stamp can be easily released after the hot stage cooling down. So the optical window (K9 glass) substrates with imprinted two-dimensional SiO₂ cylindrical photonic nanostructures show good light diffraction property. Also, our experiment demonstrates that with the imprinted sample annealing at 200${}^{\circ }$C, the density of SiO₂ will be increased and the diffraction efficiency can be further enhanced. In addition, the light splitting characteristic can still keep good for a larger (6 inch) substrate, which has a certain radian. This illustrates that this nanoimprint method can be compatible with the fluctuation of the imprinted substrates. Furthermore, as the distance between two adjacent feature nanostructures is in sub-micro scale, hexagonal symmetry diffraction pattern by the cylindrical photonic structures was realized at normal incidence of monochromatic laser ($\lambda =$532nm). The diffraction efficiency of first order is about 11.2%. Morever, the diffraction pattern and the intensity of the first diffraction order can be modulated just by changing the incident angle of the input laser.

In this work, a fast and mild in-situ oxidization hydrothermal method was developed to fabricate the nickel–cobalt layered double hydroxides (Ni–Co LDHs) on Ni foam. The Ni–Co LDHs with the nanoarrays and nanopetals structures were synthesized by in situ oxidizing Ni foam in a mixed solvent of cobalt chloride hexahydrate (CoCl${}_2\cdot 6$H₂O) and hydrogen peroxide (H₂O₂) at 90${}^{\circ }$C for 3h. The electrochemical performance tests indicate the Ni–Co LDHs electrodes have a high areal capacitance value about 17.3F/cm² at 5.0mA/cm². After 1000 cycles at 50mA/cm², the as-prepared electrodes have the high capacitance retention of 83%. Thus, the binder-free Ni–Co LDHs with high electrochemical performance are the promising electrode materials for advanced electrochemical storage energy devices including flexible power sources and supercapacitors in modern electronic systems.