Multifunctional Zn0.99−xMn0.01CuxS nanowires: Structure, luminescence and magnetism

The wurtzite-type Zn_0.99−xMn_0.01Cu_xS (x = 0, 0.003, 0.01) nanowires were prepared by a simple hydrothermal method at 180 °C. The structure and morphology of the samples were characterized by X-ray diffraction (XRD), X-ray absorption fine structure (XAFS), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), field emission scanning electron micrograph (FESEM) and X-ray photoelectron spectrum (XPS). The results showed that both the Mn²⁺ and Cu²⁺ ions substituted for the Zn²⁺ sites in the host ZnS. The ethylenediamine-mediated template was observed, which was used to explain the growth mechanism of the nanowires. The color-tunable emission can be obtained by adjusting the concentrations of Mn²⁺ and Cu²⁺ ions. The ferromagnetism was observed around room temperature.     

Ethanol-thermal synthesis of Cd1−xZnxS nanoparticles with enhanced photodegradation of 4-chlorophenol

Cd_1−xZn_xS nanoparticles were prepared by a one-pot solvothermal process from Zn(CH₃COO)₂, Cd(CH₃COO)₂ and NaS₂CNEt₂·3H₂O (sodium diethyldithiocarbamate, DDTC). The Cd_1−xZn_xS nanoparticles were characterized by X-ray powder diffraction, transmission electron microscope and high-resolution transmission electron microscope equipped with an energy-dispersive X-ray spectrometer. The absorption spectra of the Cd_1−xZn_xS nanoparticles can be tuned into visible region by modulating stoichiometric ratio between Zn and Cd. With the increase of Zn content, the Cd_1−xZn_xS nanoparticles showed an enhanced photocatalytic activity on degradation of 4-chlorophenol. The Cd_1−xZn_xS prepared under the optimal experimental condition (initial Zn/Cd = 3:1, 210 °C, 24 h, in ethanol) possessed the best photocatalytic activity. The conversion ratio could reach up to 84% after 12 h under irradiation of visible light for Cd_1−xZn_xS prepared in ethanol, which was obviously superior to those of products prepared in water. These results showed that both crystallinity and synthetic medium were responsible for the enhanced photocatalytic activity for 4-chlorophenol.     

Synthesis of β-phase Ag1−xCuxI (x = 0-0.5) solid solutions nanocrystals

A series of single β-phase nano-Ag_1−xCu_xI (x = 0-0.5) solid solutions powders were synthesized by wet-chemical-chelating reaction processing and citric acid used as complexing agent. The Ag_1−xCu_xI powders were determined by X-ray diffraction and transmission electron microscopy. It was demonstrated that the crystalline size and lattice parameter of the Ag_1−xCu_xI powders decrease with an increase in the amount of CuI substitution. The copper in the lattice of the Ag_1−xCu_xI can effectively prevent the crystalline growth of the Ag_1−xCu_xI powders and citrate used in the Ag_1−xCu_xI powders synthesized process can accelerate single β-phase crystalline structure formation.     

The effect of Cu content on the structure of Ni1−xCuxFe2O4 spinels

A series of Ni_1−xCu_xFe₂O₄ (0 ≤ x ≤ 0.5) spinels were synthesized employing sol-gel combustion method at 400 °C. The decomposition process was monitored by thermal analysis, and the synthesized nanocrystallites were characterized by X-ray diffraction, transmission electron microscopy, infra-red and X-ray photoelectron spectroscopy. The decomposition process and ferritization occur simultaneously over the temperature range from 280 °C to 350 °C. TEM indicates the increase of lattice parameter and particle size with the increase of copper content in accordance with the XRD analysis. Cu²⁺ can enter the cubic spinel phase and occupy preferentially the B-sites within x = 0.3, and redundant copper forms CuO phase separately. A broadening of the O 1s region increases with the increment of copper content compared to pure NiFe₂O₄, showing different surface oxygen species from the spinel and CuO. Cu²⁺ substitution favors the occupancy of A-sites by Fe³⁺.     

Optical properties of nanocrystalline Ga1−xInxSb/SiO2 films

Ga_1−xIn_xSb (x=0.19, 0.38, 0.63) nanoparticles embedded in a SiO₂ matrix were grown on the glass substrates by radio-frequency magnetron co-sputtering. X-ray diffraction patterns strongly support the existence of nanocrystalline Ga_1−xIn_xSb in the SiO₂ matrix. The changes in binding energies with Ga_1−xIn_xSb nanocrystals deposition have been directly observed by X-ray photoemission spectroscopy, and these show the existence of Ga_1−xIn_xSb nanocrystals in the SiO₂ matrix. Room-temperature Raman spectra show that the Raman peaks of the Ga_1−xIn_xSb-SiO₂ composite film have a larger red-shift of about 95.3 cm⁻¹ (longitudinal-optical mode) and 120.1 cm⁻¹ (transverse-optical mode) than that of bulk GaSb, suggesting the existence of phonon confinement and tensile stress effects. Additionally, the room-temperature optical transmission data exhibit a large blue-shift with respect to that of the bulk semiconductor due to the strong quantum confinement effect.     

Optimum IV-group ion concentrations in ZnGa2O4−xMx (M=S, Se, Te) phosphors for enhancement of luminescence

The ZnGa₂O_4−xM_x (M=S, Se, and Te ) samples with varying S, Se, and Te concentrations are synthesized through solid-state reactions. The X-ray diffraction patterns of ZnGa₂O_4−xM_x (M=S, Se, and Te) show that the positions of the (4 0 0) diffraction peak gradually shift to lower angles due to the doping of VI-group ions (S, Se, and Te) with larger ionic radius than oxygen. For ZnGa₂O_4−xS_x samples, the solubility limit is found to be about x=0.30. The cathodoluminescence measurements on ZnGa₂O_4−xM_x samples show that the optimized S, Se, and Te concentrations with the highest cathodoluminescence intensities are 0.10, 0.05, and 0.03, respectively. The luminous intensity of ZnGa₂O_3.95Se_0.05 is four times higher than that of ZnGa₂O₄. Thus, ZnGa₂O_3.95Se_0.05 can be a promising candidate phosphor for FED applications.     

Materials with layered structures XIII: electrical and optical properties of layered chalcogenides in the system CoIn2S4-CoIn2Se4

The system CoIn₂S_4xSe_4(1−x) has been investigated by X-ray powder methods on samples quenched at 700 °C. The spinel type phase has a phase width of 1≥x>0.9. A new layered compound is formed for 0.9>x>0.45 which crystallizes with the α-FeGa₂S₄-type with a=392.6 pm and c=1270.3 pm (x=0.5) for the hexagonal cell. Platelike crystals of the layered phase are obtained by transport reactions with iodine in a temperature gradient 750→700 °C. The band gaps of these crystals measured by optical absorption vary from 1.2 to 1.4 eV. The electrical conductivities of the crystals are found in the order of 10⁻⁵ Ω⁻¹ cm⁻¹.     

Luminescence properties of Ca1−xSrxSe:Ce phosphors and their potential application for GaN-based LEDs

A series of solid solution phosphors Ca_1−xSr_xSe:0.02Ce³⁺ were prepared using high-temperature solid-state reaction technique. Their diffuse reflectance and luminescent spectra at room temperature were investigated and discussed. The optical band gap E_g energies of CaSe and SrSe were derived. Because of its broad band absorption in the range of 400-500 nm, Ca_1−xSr_xSe:Ce³⁺ can suit the application requirements for GaN-based light-emitting diodes (LEDs). The emission wavelength and the coordinates systematic shift from yellowish green to bluish green with an increase in x of Ca_1−xSr_xSe:Ce³⁺. Using Dorenbos's empirical equation, the values of energies of the lowest f-d transition absorption E, redshift D and Stokes shift ΔS for Eu²⁺ in the same host were predicted. The results were in good agreement with the experimental data.     

Structural study by X-ray diffraction and transmission electron microscopy of the misfit compound (SbS1−xSex)1.16(Nb1.036S2)2

In the Sb-Nb-S-Se system, a new misfit layer compound (MSL) has been synthesized and its structure was determined by combining single crystal X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. It presents a composite crystal structure formed by (SbS_1−xSe_x) slabs stacking alternately with double NbS₂ layers and both can be treated as separate monoclinic subsystems. The (SbS_1−xSe_x) slabs comprise a distorted, two-atom-thick layer with NaCl-type structure formed by an array of {SbX₅} square pyramids joined by edges (X: S, Se); the NbS₂ layers consist of {NbS₆} trigonal prisms linked through edge-sharing to form sheets, just as in the 2H-NbS₂ structure type. Both sublattices have the same lattice parameters a = 5.7672(19) Å, c = 17.618(6) Å and β = 96.18(3)°, with incommensurability occurring along the b direction: b₁ = 3.3442(13) Å for the NbS₂ subsystem and b₂ = 2.8755(13) Å for the (SbS_1−xSe_x) subsystem. The occurrence of diffuse scattering intensity streaked along c^* indicates that the (SbS_1−xSe_x) subsystem is subjected to extended defects along the stacking direction.     

Synthesis and electrical properties of ordered perovskite oxide Cd3−x−yCuxAyTeO6 (A = Li, Na; 0.00 ≤ x, y ≤ 0.15)

Polycrystalline Cd_3−x−yCu_xA_yTeO₆ (A = Li, Na) samples were prepared by solid-state reaction, and their crystal structure and electrical properties were investigated. In Cd_3−xCu_xTeO₆ and Cd_3−yA_yTeO₆ (A = Li, Na), the maxim solubility of x and y was 0.15 and 0.15 for A = Li, 0.05 for A = Na, respectively. For co-substituted samples Cd_2.9−yCu_0.1Li_yTeO₆ and Cd_2.9−yCu_0.1Na_yTeO₆, the maxim solubility of x was the same as single substitution above-mentioned. The alkali-metal substituted samples Cd_3−yA_yTeO₆ (A = Li, Na) showed a negative Seebeck coefficient, which indicates that the major conduction carriers are electron. On the other hand, the co-substituted samples Cd_2.9−yCu_0.1A_yTeO₆ (A = Li, Na) represented a positive Seebeck coefficient, and major conduction carriers were hole through substitution by copper ions.     

Synthesis and characterization of Ni1−xZnxFe2O4 spinel ferrites from tailored layered double hydroxide precursors

In this paper, a series of pure Ni_1 − xZn_xFe₂O₄ (0 ≤ x ≤ 1) spinel ferrites have been synthesized successfully using a novel route through calcination of tailored hydrotalcite-like layered double hydroxide molecular precursors of the type [(Ni + Zn)_{1 − x − y}Fe_y²⁺Fe_x³⁺(OH)₂]^x+(SO₄²⁻)_x/2·mH₂O at 900 °C for 2 h, in which the molar ratio of (Ni²⁺ + Zn²⁺)/(Fe²⁺ + Fe³⁺) was adjusted to the same value as that in single spinel ferrite itself. The physico-chemical characteristics of the LDHs and their resulting calcined products were investigated by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and Mössbauer spectroscopy. The results indicate that calcination of the as-synthesized LDH precursor affords a pure single Ni_1 − xZn_xFe₂O₄ (0 ≤ x ≤ 1) spinel ferrite phase. Moreover, formation of pure ferrites starting from LDHs precursors requires a much lower temperature and shorter time, leading to a lower chance of side-reactions occurring, because all metal cations on the brucite-like layers of LDHs can be uniformly distributed at an atomic level.     

Fluorite-like phases in the BaF2-BiF3-Bi2O3 system—synthesis, conductivity and defect clustering

A fluorite-like solid solution Ba_1 − xBi_xO_zF_{2 + x − 2z} on the basis of cubic BaF₂ was synthesised in the BaF₂-Bi₂O₃-BiF₃ system and the homogeneity range at 873 K was determined. The samples were studied by X-ray powder diffraction and electron diffraction, and their transport properties were measured by the complex impedance method at 300-623 K. Tendencies of variation of lattice parameters and transport properties were determined. These tendencies are discussed on the basis of a defect clustering hypothesis. Thermal treatment at 573 K of the solid solution, quenched from 873 K results in the formation of a new ordered tetragonal fluorite-like phase with lattice parameters a = 9.5355(4) Å, c = 18.151(1) Å.     

Crystallization and microstructure of glasses in the system Na2O/MnO/SiO2/Fe2O3

Glasses with the compositions (100 − x)(0.16Na₂O/0.10MnO/0.74SiO₂)/xFe₂O₃, (x = 5-30) and 16Na₂O/10MnO/(74 − y)SiO₂/yFe₂O₃ (y = 5-30) were studied using X-ray diffraction and scanning electron microscopy. The effect of the chemical composition and the thermal history on the phase formation and the resulting microstructure was investigated. During cooling, the precipitation of ferrimagnetic solid solutions Fe₃O₄/Mn₃O₄ was observed. These crystals show dendritic or platelet shape, whereby the platelets are ferromagnetic and the dendrites - mainly paramagnetic. The tendency towards crystallization can be suppressed by increasing the Na₂O-concentration. In contrast to glasses without manganese oxide, the precipitation of hematite is not observed. Therefore, the addition of reducing agents is not required, in order to crystallize large volume concentrations of the ferrimagnetic phase.     

Novel composition above the limit of Bi:Zr solid solution; synthesis and physical properties of Bi1.33Zr0.67O3+δ

This paper presents an increase to x = 0.67 of the zirconium content in the conductive Bi_2−xZr_xO_3+δ solid solution. Complete incorporation of Zr in the β_III-Bi₂O₃ structure, confirmed by X-ray powder diffraction, has produced a phase with a lower volume and superior conductivity than those predicted by an earlier study. The observed β_III-δ Bi_2−xZr_xO_3+δ phase transition around 730 °C has been characterised for the first time and shows a segregation of a mixture of predominantly γ-Bi₂O₃ and approximately 30% of the ZrO₂, before total reincorporation of the Zr in the high temperature δ-phase.     

Rietveld refinement of the semiconducting system Bi2−xFexTe3 from X-ray powder diffraction

The semiconducting system Bi_2−xFe_xTe₃ (x = 0.0, 0.02, 0.04 and 0.08) was synthesized at 1000 °C for 30 h. The scanning electron microscope (SEM) image reveals the tendency of the Bi_2−xFe_xTe₃ system to form a sheet structure with more pronounced alignment and to enhance the formation of some microstructure tubes. The structure of the system under study was refined on the basis of X-ray powder diffraction data using the Rietveld method. The analysis revealed the complete miscibility of Fe in the Bi₂Te₃ matrix and hence the formation of single phase. The system crystallizes in the space group R-3m [1 6 6]. The lattice parameters and the unit cell size slightly change by the incorporation of Fe. The refinement of instrumental and structural parameters led to reliable values for the R_B, R_F and Chi².     

Hydrothermal synthesis of nanocrystalline MxZn1−xFe2O4 (M=Ni, Mn, Co; x=0.40-0.60) powders

A series of nanocrystalline M_xZn_1−xFe₂O₄ (M=Ni, Mn and Co; x=0.40-0.60) powders have been successfully prepared via hydrothermal process and characterized by XRD, TEM and IR techniques. The effects of reaction temperature and the initial pH value of the starting suspension solution on the particulate properties such as the particle size and morphology are discussed. IR spectra indicate that there are no hydroxyl in as-prepared Ni_xZn_1−xFe₂O₄ and Co_xZn_1−xFe₂O₄ powders, while there are obvious hydroxyl adsorption on the IR spectrum of Mn_xZn_1−xFe₂O₄ powder.     

Electronic structure and photocatalytic water splitting of lanthanum-doped Bi2AlNbO7

Bi_2−xLa_xAlNbO₇ (0 ≤ x ≤ 0.5) photocatalysts were synthesized by the solid-state reaction method and characterized by powder X-ray diffraction (XRD), infrared (IR) spectra and ultraviolet-visible (UV-vis) spectrophotometer. The band gaps of the photocatalysts were estimated from absorption edge of diffuse reflectance spectra, which were increased by the doping of lanthanum. It was found from the electronic band structure study that orbitals of La 5d, Bi 6p and Nb 4d formed a conduction band at a more positive level than Bi 6p and Nb 4d orbitals, which results in increasing the band gap. Photocatalytic activity for water splitting of Bi_1.8La_0.2AlNbO₇ was about 2 times higher than that of nondoped Bi₂AlNbO₇. The increased photocatalytic activity of La-doped Bi₂AlNbO₇ was discussed in relation to the band structure and the strong absorption of OH groups at the surface of the catalyst.     

Thin films of supersaturated substitutional solid solutions CuxPb1−xS1−δ : chemical deposition, crystal structure and chemical sensor application

Thin films of supersaturated Cu_x^(I)Pb_1−xS_1−δ solid solutions (0.038<x≤0.083) having the B1 (NaCl) cubic structure have been produced for the first time by hydrochemical co-deposition of lead and copper sulfides from a citrate-ammonia reaction mixture at a temperature from 333 to 353 K. Regular features of formation of Cu_x^(I)Pb_1−xS_1−δ solid solutions depending on the composition of the reaction mixture have been established. The methods of X-ray and neutron diffraction, electron microscopy, and Raman spectroscopy were used to examine the crystal structure, the phase composition, and the morphology of lead (II) and copper (I) sulfide films and films of solid solutions. It is shown that copper is present in the Cu_x^(I)Pb_1−xS_1−δsolid solution as a monovalent ion. Photosensitivity and sensor properties of films of Cu_x^(I)Pb_1−xS_1−δ solid solutions have been analyzed.     

Re-examination of the structural properties of solid solutions SrxCa1−xCO3

We have re-examined the evolution of orthorhombic cell parameters as a function of the substitution parameter x in solid solutions Sr_xCa_1−xCO₃ in order to clarify contradictory results found in the literature. Calcium carbonate has been synthesized in the presence of Sr²⁺ ions (Sr/Ca molar ratio ranging from 10⁻² to 1), using experimental conditions that previously allowed us to obtain monophasic aragonite. The precipitates obtained have been analysed using powder X-ray diffractometry (XRD) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES). The powder XRD data confirm the occurrence of purely monophasic strontian-aragonites. Moreover, the cell parameters as well as the substitution parameter x have been refined for 0 < x < 0.5 against powder XRD data through Rietveld refinement. On the other hand, x was deduced from chemical analysis by ICP-AES. The agreement between both techniques is very satisfactory. The evolution of the cell parameters as a function of x is found to be linear within the studied range, this feature being confirmed for the overall domain (0 ≤ x ≤ 1) if one takes into account the cell parameters of aragonite CaCO₃ and strontionite SrCO₃. This result, that is consistent with the existence of continuous solid solutions obeying the Vegard's law in the Sr_xCa_1−xCO₃ system, contradicts previously published assertions.     

Oxide-ion conductivity in CuxCe1−xO2−δ (0 ≤ x ≤ 0.10)

Up to 10 at.% of copper readily substitutes for cerium in ceria. It is found that at oxygen partial pressures between 0.21 atm and 10⁻⁵ atm, Cu_xCe_1−xO_2−δ (0 ≤ x ≤ 0.10) solid solution behave as an oxide-ion electrolyte. Interestingly, Cu_0.10Ce_0.90O_2−δ exhibits the oxide-ion conductivity of ca. 10⁻⁴ Ω⁻¹ cm⁻¹ at 600 °C at an oxygen partial pressure of 10⁻⁵ atm.