Mechanochemical synthesis and ionic conductivity of lanthanum phosphosilicate oxyapatites

Lanthanum phosphosilicate apatites with the chemical formula Sr_10–xLa_x(PO₄)_6–x(SiO₄)_xO, where 0 ≤ x ≤ 6, usually prepared by a solid-state reaction at about 1400 °C, were synthesized via the mechanochemical method at room temperature. The samples were characterized using powder X-ray diffraction, infrared spectroscopy and thermal analysis. The results showed that the prepared products were carbonated apatites and no secondary phase was detected. The realization of the milling under a controlled atmosphere can lead to oxyapatites containing no carbonates. The ionic conductivity of the Sr₆La₄(PO₄)₂(SiO₄)₄O sample was investigated by using impedance spectroscopy. The highest ionic conductivity value of 1.522 × 10⁻⁶ S·cm⁻¹ was found at 800 °C. In the investigated temperature range, the activation energy is of 0.85 eV.     

Research on optical band gap of the novel GeSe2–In2Se3–KI chalcohalide glasses

The glass-forming region of the GeSe₂–In₂Se₃–KI system was reported firstly. The dependence of physical, thermal and optical properties on compositions as formula of (1 ? x)(0.8GeSe₂–0.2In₂Se₃)–xKI (x = 0, 0.1, 0.2, 0.3) chalcohalide glasses was investigated. The allowed direct transition and indirect transition, and Urbach energy of samples were calculated according to the classical Tauc equation. The results show that the glass system has good thermal stability and that there is an obvious blue-shift at the visible absorbing cutting-off edge. When the dissolved amount of KI increased from 0 to 30 mol%, the direct optical band gap and the indirect optical band gap were in the range from 1.617 to 1.893 eV and 1.573 to 1.857 eV. With the decrease of the molar refraction the refractive index decreases, optical band gap and metallization criterion increase. The relationship between energy band gap and metallization criterion was analyzed and the optical properties of chalcohalide glasses were summarized.     

Preparation of Ag2Se and Ag2Se1 − xTex nanowires by electrodeposition from DMSO baths

We have developed a novel electrochemical route to fabricate highly ordered stoichiometric Ag₂Se nanowire arrays by electrodeposition from non-aqueous dimethyl sulfoxide (DMSO) solutions. Cyclic voltammetry technique was used to study this cathodic deposition process. X-ray energy dispersion analysis shows that stoichiometric Ag₂Se nanowires can be obtained in a wide range of deposition condition. X-ray diffraction and electron diffraction patterns demonstrate that the as-deposited nanowires are [0 0 2] oriented orthorhombic β-Ag₂Se. Furthermore, ternary Ag₂Se_1 − xTe_x nanowires have been electrodeposited in mixed SeCl₄–TeCl₄ DMSO solutions.     

Structural and optical properties of sprayed Zn1−xMnxO films

In recent years the dilute magnetic semiconductors have received much attention due to the complementary properties of semiconductor and ferromagnetic behaviour. Zn_1−xMn_xO thin films have been synthesized by chemical spray pyrolysis at a substrate temperature of 400 °C with different manganese compositions that vary in the range, 0.0 ≤ x ≤ 0.25, on Corning 7059 glass substrates. The X-ray diffraction studies revealed that all the films were strongly oriented along the (002) orientation corresponding to the hexagonal wurtzite structure. The crystalline quality of the layers was found to decrease with the increase of x, however, no structural changes were observed over the ‘Mn’ composition range investigated. The optical absorption studies revealed that the energy band gap of the films followed the Vegard's law. The optical band gap of the films prepared at x = 0.15 was found to be ∼3.35 eV. The photoluminescence characteristics of Zn_1−xMn_xO films showed an emission peak at around 390 nm with a broad band about 530 nm. The details of these results were reported and discussed.     

Theoretical study on the stability and electronic property of Ag2SnO3

Bulk crystal properties of Ag₂SnO₃ were investigated with the advantage of density functional theory. The whole structure has layered feature: hexagonal metallic planes formed by Ag atoms and distorted octahedrons of SnO₆ clusters are configured alternatively along c axis of hexagonal cell. The cohesive energy is about ?2.792 eV/atom, which is less than SnO₂. The Debye temperature of Ag₂SnO₃ is about 231.6 K, and the bulk and shear moduli are 62.13 and 20.63 GPa, respectively. Band structure and DOS show the compound has a small pseudo-band gap value of 1.0 eV and so may be a semiconductor. When checking the PDOS intensity at the Fermi surface of Ag atoms, a weak metallic character can be seen. The distortion mechanism becomes less effective to reduce the total orbital energy both in SnO₂ and in Ag₂SnO₃ and as a result the bond lengths of Sn–O are intended to be isotropy.     

Synthesis,crystal structure and luminescent properties of pyrovanadates A2CaV2O7 (A = Rb,Cs)

The novel vanadium oxides Rb₂CaV₂O₇ and Cs₂CaV₂O₇ have been prepared by solid-state reaction and their crystal structures determined and refined using X-ray, neutron powder and electron diffraction data. Rb₂CaV₂O₇ and Cs₂CaV₂O₇ are isostructural, crystallizing in space group P2₁/n with unit cell parameters: a = 13.8780(1), b = 5.96394(5), c = 10.3376(1) Å, β = 104.960(1)° and a = 14.0713(2), b = 6.0934(1), c = 10.5944(1) Å, β = 104.608(1)°, respectively. Their crystal structures can be described as a framework of CaO₆ octahedra and V₂O₇ pyrogroups with alkaline metals found in the tunnels formed. Photoluminescence (PL) and PL excitation spectra of the considered pyrovanadates have been studied in the vacuum ultraviolet (VUV) to visible light (Vis) range as well as their pulse cathode luminescence (PCL) spectra and the kinetic parameters of PCL. In the PL and the PCL spectra of both pyrovanadates recorded at T = 300 K a broad band with maxima at 2.2, 2.4 eV and two shoulders (bands) at 2.0 and 2.58 eV have been observed. At T = 10 K the band at 2.0 eV becomes the main band in the spectra. Two types of luminescence centers for each pyrovanadate, with very similar excitation bands at 3.75, 4.84, 6.2, 7.3 and 9.1 eV, have been found. The nature of the luminescence centers connected with the bands at 2.0, 2.2, 2.4 and 2.58 eV is discussed.     

A Ca substitution study of NaV2O4: High-pressure synthesis of the Na1−xCaxV2O4 solid solution

Ambient pressure CaV₂O₄ and high-pressure NaV₂O₄ crystallize in the CaFe₂O₄ structure type containing double chains of edge-sharing VO₆ octahedra. Recent measurements on NaV₂O₄ reveal low-dimensional metallicity and evidence of half-metallic ferromagnetism. In contrast, CaV₂O₄ is an antiferromagnetic insulator. To explore the evolution of these ground-state behaviors, we have prepared a series of Ca-doped NaV₂O₄ compounds with the formula Na_1?xCa_xV₂O₄ (x = 0–1) using high-pressure synthesis. Samples at the Na end (x = 0–0.07) show a broad antiferromagnetic transition in the 120–160 K range in accordance with earlier reports. Transport measurements show an insulator–metal transition at x ～ 0.2. Samples with higher Ca concentrations (x = 0.4–0.7) exhibit a metal–insulator transition around 150 K. The results for the Na_1?xCa_xV₂O₄ solid solution is discussed in comparison to existing studies at the Ca- and Na-rich ends.     

Photo-luminescence studies of strontium barium niobate crystals doped with Cr3+ ions

This paper reports the photo-luminescence spectroscopic results of Strontium–Barium–Niobate, Sr_x,Ba_1−xNb₂O₅ (SBN, x = 0.61 for near congruent composition) crystals doped with Cr₂O, at cryogenic temperature (20 K). The experimental results reveal the need of re-assignment of the Cr³⁺ ions defect centres in this material. For first time, a broad emission band in the near infrared region centred at ca. 950 nm is reported. This emission band has micro-seconds decaytime constant and a FWHM band-width > 1700 cm⁻¹ and has been ascribed to the vibronically assisted ⁴T₂ → ⁴A₂ transition. A much narrower emission band centred at ca. 764 nm with milli-seconds decaytime constant and a FWHM band-width of ca. 170 cm⁻¹ is correlated to the ²E → ⁴A₂ radiative transition (R-line).     

Gamma ray induced changes on vibrational spectroscopic properties of strontium alumino-borosilicate glasses

The present investigation reports the effect of influence of aluminum ions on radiation damage of strontium borosilicate glasses studied by means of spectroscopic (viz., optical absorption (OA), infrared and Raman spectra). The composition of the glasses chosen for the study is 40SrO–xAl₂O₃–(15-x) B₂O₃–40SiO₂ (x = 5, 7.5, 10), all in mol%. The glasses were synthesized by conventional melt quenching method. Later, the samples were exposed to gamma (γ) radiation dose of strengths 10 kGy and 30 kGy with a dose rate of 1.5 Gy/s using ⁶⁰Co as radiation source. The infrared spectra (IR), Raman spectra and optical absorption (OA) spectra of the samples were recorded at ambient temperature before and after irradiation. The OA spectra of the pre-irradiated samples do not exhibit any absorption bands in the UV–vis regions and IR and Raman spectra exhibited conventional vibrational bands due to different borate, silicate AlO₄ and AlO₆ structural units. The OA spectra of post irradiated samples exhibited a broad absorption band in the wavelength region 600–750 nm; it is attributed to electron trapped color centers. The intensity of this peak is observed to increase with increase of the γ-ray dose. Considerable changes in the intensities of various bands in the IR and Raman spectra were also observed. The changes were explained based on structural modifications taking place in the glass network due to γ-ray irradiation and finally it is concluded that the glasses mixed with 10.0 mol% of Al₂O₃ are relatively more radiation resistant.     

Doping effects of Yb3+ on the crystal structures,nanoparticle properties and electrical behaviors of ZrO2 derived from a facile urea-based hydrothermal route

Weakly-agglomerated nanocrystalline (ZrO₂)_1−x(Yb₂O₃)_x (x=0.02–0.2) powders with high surface area (109–151 m² g⁻¹) were synthesized by a two-step hydrothermal process in the presence of urea: a stock solution of metal nitrates and urea was heated at 80 °C for 24 h and then at 180 °C for 48 h. For x=0.04–0.2, the as-derived powders were an assembly of uniform nanoparticles with well-defined edges in the size between 6.1–8.4 nm. Before and after calcination at 800 °C, the lattice parameters, microstrain and surface area of the (ZrO₂)_1−x(Yb₂O₃)_x samples tended to increase with Yb³⁺ concentration; while, the average crystallite size decreased correspondingly. In the Arrhenius plots over the measurement temperature range of 400–800 °C, the bulk ionic conductivity of the compacts sintered at 1400 °C for 24 h showed a maximum value at the composition of x=0.08 in cubic structure, with an activation energy of 0.89 eV. At 800 °C, σ_b=0.049 S cm⁻¹ for x=0.08.     

Photocatalytic activity of a novel Bi-based oxychloride catalyst Na0.5Bi1.5O2Cl

A Bi-based oxychloride Na_0.5Bi_1.5O₂Cl with a layered structure as a novel efficient photocatalyst was studied in the present paper. The powder was synthesized by a solid state reaction method. It was characterized by X-ray diffraction, scanning electron microscope and UV–vis diffuse reflectance spectrum. Degradation of methyl orange was used to evaluate the photocatalytic activity. The as-synthesized Na_0.5Bi_1.5O₂Cl has a smaller optical band gap of 3.04 eV than BiOCl (E_g = 3.44 eV). It possesses a fair visible-light-response ability. The UV-induced photocatalytic activity follows the decreasing order of BiOCl > Na_0.5Bi_1.5O₂Cl > TiO₂, different from the order of Na_0.5Bi_1.5O₂Cl > TiO₂ > BiOCl under visible light irradiation. The dispersion of Pt over Na_0.5Bi_1.5O₂Cl leads to an obvious increase in the photocatalytic performance. The internal electric fields between [Na_0.5Bi_1.5O₂] and [Cl] slabs favor the efficient separation of photostimulated electron–hole pairs.     

Exploration of spray pyrolysis technique in preparation of absorber material CFATS: Unprecedented hydrophilic surface and antibacterial properties

In this study, we achieve the production of nontoxic Cu₂Fe_1-xAl_xSnS₄ films (x = 0, 0.25, 0.50, 0.75 and 1) by substituting Fe with Al atoms. Physical properties of the investigated films were studied using: Energy dispersive X-ray spectrometry (EDX), scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, spectrophotometer and drop shape analysis system (DSA). The formation of new quaternary Cu₃Al_0.6Sn₁S₆ (CATS) chalcogenide for x = 1 was proven from EDX study. Notably, the major diffraction peaks were located at 2θ = 28.34°, 47.43° and 55.93° which are respectively tagged as (1 1 2), (2 0 4), and (3 1 2) plans, confirming the stannite crystal structure of Cu₃Al_0.6Sn₁S₆ film. The morphological states show a nanofiber structure accompanied with voids and cavities for CATS films. Tauc-relation plot reveals direct energy bandgap, close to 1.52 eV, which proves the absorber film type of Cu₃Al_0.6Sn₁S₆. The effluent toxicity of the obtained thin films has been assessed using the inhibition of Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria and indicated good antibacterial activity of the CATS/SnO₂:F heterojunction. The viability rates against S. aureus achieved 40 %, 31 % and 15% for SnO₂:F, Cu₃Al_0.6Sn₁S₆ films and CATS/SnO₂:F heterojunction. These results highlight the great antibacterial activity of coupled CATS/SnO₂:F. Therefore this research underscores the effectiveness of CATS/SnO₂:F surface which demonstrates self-disinfecting and self-cleaning with hydrophilicity and high antibacterial activity.     

Synthesis,structure and properties of Ag2PdO2

The first silver palladium oxide, Ag₂PdO₂, was synthesised from a co-precipitated oxide precursor by annealing at 423–823 K, applying an oxygen pressure of 73 MPa. The crystal structure has been determined from X-ray and neutron powder diffraction data. The new compound crystallises in space group Immm. The lattice constants as determined from X-ray powder diffraction are a=4.55523(5) Å, b=3.00803(3) Å and c=9.8977(1) Å. The crystal structure constitutes a new structure type showing some features in common with the Li₂CuO₂-type. Palladium is found in a nearly square planar arrangement while silver has an almost linear co-ordination. The overall structure can be considered as a rocksalt defect structure. Ag₂PdO₂ is diamagnetic and semiconducting. The band gap, estimated from conductivity measurements in the temperature range of 240–300 K, is 0.18(2) eV.     

Annealing effects on the morphology and luminescence of cubic boron nitride based ceramics

Cubic boron nitride based ceramics with silicon were sintered at 1350 °C under a pressure of 5.0 GPa. The effects of post-annealing on grain morphology, surface morphology, and photoluminescence of Si–cBN ceramics were investigated by scanning electron microscope and room temperature photoluminescence measurements. The results showed that the annealing treatment had great influence on cBN grain morphology, rather than the surface morphology. The luminescence intensity increased with annealing temperature and annealing time. The void-net structure formed by continuous distribution of SiO_x particulate on the ceramic surface resulted in the emission band peaking at about 701.2 nm, and the tense passivation of Si by SiO_x led to the peak's low intensity. The near ultraviolet emission band peaking at about 317 nm was attributed to the oxygen vacancies formed in cBN grain surface, caused by the scavenging of oxygen from the cBN grain surface by the added Si.     

XPS/EXAFS study of cycleability improved LiMn2O4 thin film cathodes prepared by solution deposition

The influence of Sn substitution in LiMn₂O₄ thin films as a cathode has been studied via solution deposition to improve the electrochemical performance of thin film lithium batteries. LiSn_0.025Mn_1.95O₄ thin films showed the most promising performance, i.e. a high capacity retention of 77% at 10 C after the 500th cycle, due to the increased average Mn valence state. The thin films of LiSn_x/2Mn_2?xO₄ (x ? 0.10) showed significant precipitation of SnO₂ and SnO after the cycling evaluation.     

Lithium–manganese–nickel-oxide electrodes with integrated layered–spinel structures for lithium batteries

A series of lithium–manganese–nickel-oxide compositions that can be represented in three-component notation, xLi[Mn_1.5Ni_0.5]O₄ · (1 − x){Li₂MnO₃ · Li(Mn_0.5Ni_0.5)O₂}, in which a spinel component, Li[Mn_1.5Ni_0.5]O₄, and two layered components, Li₂MnO₃ and Li(Mn_0.5Ni_0.5)O₂, are structurally integrated in a highly complex manner, have been evaluated as electrodes in lithium cells for x = 1, 0.75, 0.50, 0.25 and 0. In this series of compounds, which is defined by the Li[Mn_1.5Ni_0.5]O₄–{Li₂MnO₃ · Li(Mn_0.5Ni_0.5)O₂} tie-line in the Li[Mn_1.5Ni_0.5]O₄–Li₂MnO₃–Li(Mn_0.5Ni_0.5)O₂ phase diagram, the Mn:Ni ratio in the spinel and the combined layered Li₂MnO₃ · Li(Mn_0.5Ni_0.5)O₂ components is always 3:1. Powder X-ray diffraction patterns of the end members and the electrochemical profiles of cells with these electrodes are consistent with those expected for the spinel Li[Mn_1.5Ni_0.5]O₄ (x = 1) and for ‘composite’ Li₂MnO₃ · Li(Mn_0.5Ni_0.5)O₂ layered electrode structures (x = 0). Electrodes with intermediate values of x exhibit both spinel and layered character and yield extremely high capacities, reaching more than 250 mA h/g with good cycling stability between 2.0 V and 4.95 V vs. Li° at a current rate of 0.1 mA/cm².     

Low-temperature heat capacity of sodium borosilicate glasses at temperatures from 13 K to 300 K

Thermodynamic properties of sodium borosilicate glasses {56.7 SiO₂, (43.7  − x)B₂O₃,xNa₂O} wherex =  14.4, 22.9, and 32.5, have been studied. The heat capacity was measured using an adiabatic calorimeter at temperatures between 13 K and 300 K. The thermodynamic functions were calculated from the smoothed values ofC_{p, m} . The results differ from an additive model with pure glassy SiO₂, B₂O₃, and crystalline Na₂O as components. A model based on the assumption that the contribution of structural units of glasses to the heat capacity is equal to those of glasses with the same molecular formula is proposed.     

Optical and electrical conducting properties of Polyaniline/Tin oxide nanocomposite

Polyaniline(PANI)/Tin oxide (SnO₂) hybrid nanocomposite with a diameter 20–30 nm was prepared by co-precipitation process of SnO₂ through in situ chemical polymerization of aniline using ammonium persulphate as an oxidizing agent. The resulting nanocomposite material was characterized by different techniques, such as X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Fourier Transform Infrared spectroscopy (FT-IR) and Ultraviolet–Visible spectroscopy (UV–Vis), which offered the information about the chemical structure of polymer, whereas electron microscopy images provided information regarding the morphology of the nanocomposite materials and the distribution of the metal particles in the nanocomposite material. SEM observation showed that the prepared SnO₂ nanoparticles were uniformly dispersed and highly stabilized throughout the macromolecular chain that formed a uniform metal-polymer nanocomposite material. UV–Vis absorption spectra of PANI/SnO₂ nanocomposites were studied to explore the optical behavior after doping of nanoparticles into PANI matrix. The incorporation of SnO₂ nanoparticles gives rise to the red shift of π–π¹ transition of polyaniline. Thermal stability of PANI and PANI/SnO₂ nanocomposite was investigated by thermogravimetric analysis (TGA). PANI/SnO₂ nanocomposite observed maximum conductivity (6.4 × 10^?3 scm^?1) was found 9 wt% loading of PANI in SnO₂.     

The role of ligand coordination on the spectral features of Yb3+ ions in lead aluminum silicate glasses

The glasses of the composition (40 ? x)PbO–(5 + x)Al₂O₃–54SiO₂:1.0Yb₂O₃ (in mol%) with x ranging from 5 to 10 have been synthesized. The IR spectral studies of these glasses have indicated that there is a gradual transformation of Al³⁺ ions from tetrahedral to octahedral coordination with increase of Al₂O₃ content in the glass network. The optical absorption and luminescence spectra have exhibited bands originating from ²F_7/2 → ²F_5/2 and ²F_5/2 → ²F_7/2 transitions, respectively. From these spectra, the absorption and emission cross-sections and fluorescence lifetime of Yb³⁺ ions have been evaluated. Quantitative analysis of these data indicated a decreasing radiative trapping and increasing fluorescence lifetime of Yb³⁺ ions with increasing Al₂O₃ content. This may be explained by structural variations in the vicinity of Yb³⁺ ions due to variation in the concentration of Al₂O₃ in the glass network.     

Structural and electrochemical properties of a porous nanostructured SnO2 film electrode for lithium-ion batteries

A B₂O₃-doped SnO₂ thin film was prepared by a novel experimental procedure combining the electrodeposition and the hydrothermal treatment, and its structure and electrochemical properties were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) analysis, energy dispersive X-ray (EDX) spectroscopy and galvanostatic charge–discharge tests. It was found that the as-prepared modified SnO₂ film shows a porous network structure with large specific surface area and high crystallinity. The results of electrochemical tests showed that the modified SnO₂ electrode presents the largest reversible capacity of 676 mAh g^?1 at the fourth cycle, close to the theoretical capacity of SnO₂ (790 mAh g^?1); and it still delivers a reversible Li storage capacity of 524 mAh g^?1 after 50 cycles. The reasons that the modified SnO₂ film electrode shows excellent electrochemical properties were also discussed.