The state of tin impurity atoms in vitreous germanium chalcogenides

Tin atoms formed after the radioactive decay of the ^119mmSn and ¹¹⁹Sb impurity atoms in the structure of Ge _x S_{1 ? x} and Ge _x Se_{1 ? x} glasses are stabilized in the form of Sn²⁺ and Sn⁴⁺ centers or in germanium nodes (after ^119mmSn decay), or in the nodes of structural units formed by ¹¹⁹Sb atoms. The Sn²⁺ and Sn⁴⁺ centers correspond to the ionized states of amphoteric two-electron tin center with negative correlation energy. ¹¹⁹Sn atoms formed after the radioactive decay of the ^119mTe atoms in the structure of Ge _x S_{1 ? x} and Ge _x Se_{1 ? x} glasses are stabilized in both chalcogen and germanium nodes.     

Mechanochemical stability of Ge1 − x − y Sn y Te x glasses

The mechanochemical stability of glasses in the Ge_{1 ? x ? y} Sn _y Te _x system is investigated. It is found that tin in Ge_{1 ? x ? y} Sn _y Te _x vitreous alloys forms a system of sp ³ chemical bonds and that Ge_{1 ? x} Sn _x Te solid solutions are formed in crystalline alloys. The dispersion of glasses at room temperature in air is accompanied by the precipitation of the SnO₂ amorphous phase.     

Structural and electrochemical studies of undoped and In3+-doped co-binary Cu2-xTe and Bi2Te3 thin films for aqueous Na–S batteries

WO₃ electrodes coated with co-binary Cu_2-xTe and Bi₂Te₃ thin films were fabricated for sodium-sulfur (Na–S) batteries. Film fabrication was controlled by adjusting the pH of the solution and the indium doping concentration. The phases of orthorhombic CuTe and hexagonal Cu₂Te with rhombohedral Bi₂Te₃ were formed on the WO₃ electrode. After In³⁺ doping, In³⁺ ions act as Frenkel defects in the Cu_2-xTe structure. This indicated that In³⁺ ions are located at interstitial sites in the Cu_2-xTe structure with higher defect creation energy. Furthermore, more interconnected-like nanoparticles and reduced porosity were observed, thereby indicating that indium segregation with grain boundaries presented and contributed to an enhancement of the surface mobility, nucleation density, and a smoother surface. For electrochemical characteristics, a polysulfide solution was used as a redox electrolyte for ion transport. Optimization of the pH and indium concentration attributed to improve the exchange current density (J₀) and time responses for the colored and bleached states because of faster movement of Na⁺ and S²⁻ ions during inter/de-intercalation. Furthermore, optimization of the electrode by adjusting the pH and doping with indium is advantageous for both Na–S and rechargeable batteries because of long life cycle, reasonably high power and energy density of 306 W/kg and 9.35 Wh/kg, respectively. The highest specific capacity (C_s) values of the charge and discharge cycles for In³⁺-doped electrodes are ∼ 21 and 19 mAh/g, respectively with the coulombic efficiency approximates 100% (average value of ∼96%). This approach may provide a general path for the fabrication of undoped and In³⁺-doped co-binary Cu_2-xTe and Bi₂Te₃ films on WO₃ electrodes and may increase our knowledge regarding Na–S batteries for further performance improvement.     

Galvanic displacement of BixTey thin films from sacrificial iron group thin films

Bi_xTe_y thin films synthesized by galvanic displacement were systematically investigated by observing open circuit potential (OCP), surface morphology, microstructure and film composition. Surface morphologies and crystal structures of synthesized Bi_xTe_y thin films were strongly depended on the type of the sacrificial materials (i.e., nickel (Ni), cobalt (Co) and iron (Fe)). Galvanically deposited Bi_xTe_y thin films from the sacrificial Ni and Co thin films exhibited Bi₂Te₃ intermetallic compounds and hierarchical structures with backbones and sub-branches. A linear relationship of deposited Bi content in Bi_xTe_y thin films as a function of [Bi³⁺]/[HTeO₂⁺] ratio (within a range of less than 0.8) in the electrolyte was also observed. Surface morphologies of Bi_xTe_y thin films were altered with the film composition.     

Novel S,N co-doped Ba2In2-xCrxO5+y oxides: Synthesis and optical properties

The (S, N) co-doped Ba₂In_2-xCr_xO_5+y (0 ≤ x ≤ 0.5) oxides are successfully obtained by mixing the Ba₂In_2-xCr_xO_5+y oxides and thiourea through a simple ball milling method followed by sintering at 400 °C for 3 h. The colors of the compounds change from orange-brown to yellow-green after reacting with thiourea. When Cr amount is small (x = 0.1), the crystal structure of (S, N) co-doped Ba₂In_2-xCr_xO_5+y is orthorhombic Ba₂In₂O₅ phase. When x ≥ 0.3, the crystal structure of the sample is cubic BaInO_2.5 phase. And this phase transition is the same as Ba₂In_2-xCr_xO_5+y. XPS results reveal that Cr⁶⁺ in Ba₂In_2-xCr_xO_5+y (0 ≤ x ≤ 0.5) oxides are reduced to Cr³⁺ after sintering. S exists in both cation and anion forms, and N exists in substitutional forms. UV–Vis analysis indicates that the yellow-green hue comes from the d-d transition of Cr³⁺, and the doping of S, N ions leads to a red shift of the absorption edge of the samples.     

The effect of magnetic field on the impurity binding energy of shallow donor impurities in a Ga1?xInxNyAs1?y/GaAs quantum well

Using a variational approach, we have investigated the effects of the magnetic field, the impurity position, and the nitrogen and indium concentrations on impurity binding energy in a Ga_1−xIn_xN_yAs_1−y/GaAs quantum well. Our calculations have revealed the dependence of impurity binding on the applied magnetic field, the impurity position, and the nitrogen and indium concentrations.     

Microwave dielectric characteristics of tungsten bronze-type Ba4Nd28/3Ti18-yGa4y/3O54 ceramics with temperature stable and ultra-low loss

A series of high-k Ba₄Nd_28/3Ti_18-yGa_4y/3O₅₄ (0≤y≤2, BNTG) ceramics with temperature stable and ultra-low dielectric loss were synthesized via the conventional solid-state reaction. The main phase of all BNTG ceramics demonstrated an orthorhombic tungsten-bronze structure, but the impurity phase (gallium-rich phase) was found in BNTG (y = 2) ceramic. Partial substitution of Ga³⁺ for Ti⁴⁺ in B-site was a valid method to improve the temperature stability and dielectric loss of BNTG ceramics. The variation of ε_r values of BNTG ceramics was dominated by the ionic polarizability. The ultra-low dielectric loss (ultra-high Q × f values) was associated with grain size, suppression of Ti³⁺ and impurity phase. The decrease of TCF values was highly dependent on the tilting of Ti-O octahedra and impurity phase. Finally, outstanding combination dielectric characteristics were achieved for BNTG microwave ceramics at y = 1.5 (ε_r = 72.8, Q × f = 14,600 GHz, TCF=+4.1 ppm/°C) and at y = 2 (ε_r = 70.3, Q × f = 15,500 GHz, TCF=+3.9 ppm/°C).     

Charge state of tin atoms substituting for tellurium atoms in the structural network of the Ge1 ? x ? y Sn y Te x glasses

The Ge_{1 − x − y} Sn _y Te _x vitreous alloys are studied using ¹¹⁹Sn M?ssbauer spectroscopy. It is found that the quadruply charged tin ions substituting for germanium in the vitreous alloys under investigation forms an sp ³ system of chemical bonds, whereas the doubly charged tin ions substituting for tellurium exhibit a metallic character of bonds with tellurium atoms in its own local environment. Original Russian Text ? E.S. Khuzhakulov, 2007, published in Fizika i Khimiya Stekla.     

Structural,magnetic, thermal and optical properties of Sn2+ cation doped magnetite nanoparticles

Tin doped nanomagnetites, Sn_xFe_3-xO₄, were synthesized with various concentrations of Sn²⁺ ion (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) by co-precipitation method. XRD, VSM, TG-DTA, SEM-EDX and UV–Vis were used to characterize and study the structural, magnetic, thermal, and optical properties of Sn_xFe_3-xO₄ nanoparticles. XRD confirmed the presence of cubic structure and spinel phase of tin doped magnetites. The d-spacing, lattice parameter, density, crystallite size and cation distribution were derived from the XRD analysis. The M − H curves exhibited changes in saturation magnetization (M_s), coercive field (H_c), remanent magnetization (M_r) and susceptibility (χ), with increasing concentration of non-magnetic Sn²⁺ ions. Differential thermal analysis was used to study the thermal stability of Sn_xFe_3-xO₄ nanoparticles. The SEM images revealed the surface morphology of the nanoparticles and the EDX spectra showed an increase in the Sn content and a corresponding decrease in the Fe content for the tin doped samples. The optical bandgap was found to be centered at 3.9 eV for the synthesized materials. This systematic study may be the first comprehensive report on synthesis and characterization of tin doped magnetites.     

Two-electron tin centers formed in chalcogenide glasses as a result of nuclear transformations

The ^119mSn impurity atoms formed as a result of the radioactive transformation of the ^119mmSn parent atoms in the structure of glasses in the As-S and As-Se systems and the As₂Te₃ glass are involved in the glass composition in the form of Sn⁴⁺ ions. The ^119mSn impurity atoms formed after the radioactive decay of the ¹¹⁹Sb atoms in the structure of glasses in the As-S and As-Se systems are located in the arsenic sites and play the role of two-electron centers with a negative correlation energy. For the As₂Te₃ glass, the ^119mSn atoms formed in a similar manner are electrically inactive. The larger part of the ^119mSn daughter atoms, which are formed after the radioactive decay of the ^119mTe parent atoms in glasses of the As-S and As-Se systems and in the As₂Te₃ glass, are located in the chalcogen sites and are electrically inactive. The significant recoil energy of the daughter atoms in the case of decay of the ^119mTe atoms leads to the appearance of displaced ^119mSn atoms.     

Synthesis and thermoelectric properties of ceramics based on barium-strontium metaplumbates

Ceramics with composition Ba_{1 ? x} Sr _x Pb_{1 + y} O_{3 + 2y} (x = 0.6, 0.8; y = 0.0, 0.1, 0.2) was synthesized by solid-state method; its phase composition, crystal structure, and thermal, electrophysical, and thermoelectric properties were studied. The electronic and lattice contributions to thermal conductivity of the ceramics were separated; the linear thermal expansion coefficient (LTEC, α), power factor (P), and thermoelectric quality factor (ZT) were calculated. Ceramics with composition Ba_0.2Sr_0.8Pb_{1 + y} O_{3 + 2y} (P ₁₀₀₀ = 1.36 mW m^?1 K^?2 for y = 0.1, ZT ₄₂₃ = 0.033 for y = 0.2) containing lead oxide impurity, in addition to the major phase (barium-strontium metaplumbate), was found to possess the best thermoelectric properties.     

Crystal structure,phonon modes and dielectric properties of B site ordered ABiLiTeO6 (A = Ba,Sr) double perovskites

ABiLiTeO₆ (A = Ba, Sr) double perovskite oxides were synthesised through conventional solid - state ceramic route. X-Ray diffraction patterns indicated pseudocubic symmetry for both compounds. Deconvoluted Raman spectra using Lorentzian function gave 7 first order Raman modes for both BaBiLiTeO₆ and SrBiLiTeO₆ whereas Infrared spectroscopy gave 8 modes for BaBiLiTeO₆ and 9 modes for SrBiLiTeO₆. Observed phonon modes were in good agreement with the corresponding group theoretical predictions for space group I4/m for both compounds. Rietveld refinement of the XRD patterns also confirmed I4/m space group for ABiLiTeO₆ (A = Ba, Sr) with 1:1 B site ordering of Te⁶⁺ and Li⁺ cations. The random occupancy of Ba²⁺ and Bi³⁺ at the A site in BaBiLiTeO₆ whereas Sr²⁺ and Bi³⁺ in SrBiLiTeO₆ were revealed from Rietveld refinement. Microstructure of both the compounds gave average grain size of less than 3?µm. At 1?MHz, BaBiLiTeO₆ and SrBiLiTeO₆ possess porosity corrected dielectric constants of 49.5 and 34.4 and dielectric losses of 0.029 and 0.028 respectively.     

Microwave dielectric properties of Li3A3Te2O12 (A = Y,Yb) garnets for low temperature cofired ceramic technologies

Te⁶⁺-containing microwave dielectric ceramics Li₃A₃Te₂O₁₂ (A = Y, Yb) with low firing temperatures were prepared using the solid-state reaction method. Li₃Y₃Te₂O₁₂ and Li₃Yb₃Te₂O₁₂ can be obtained as garnet single-phase ceramics with low sintering temperatures of 940 ℃ and 950 ℃, respectively. The cations, such as Li⁺, Te⁶⁺, and Y³⁺/Yb³⁺, fully occupied the tetrahedral, octahedral, and dodecahedral sites of garnet structure, respectively. Li₃A₃Te₂O₁₂ (A = Y, Yb) ceramics exhibit ε_r ～ 7.83 ± 0.2 and 5.94 ± 0.2, Q × f ～ 47,800 ± 500 GHz and 41,800 ± 500 GHz, and τ_f ～ –47 ± 3.0 ppm/°C and –76 ± 3.0 ppm/°C, respectively. The full width at half-maximum (FWHM) values of the A_1g Raman mode correlate negatively with the Q × f values. Moreover, Li₃A₃Te₂O₁₂(A = Y, Yb) ceramics possess good chemical compatibility with the Ag electrode, making them promising candidates for low-temperature cofired ceramics (LTCC) technologies.     

Effect of glass composition on the physical properties and luminescence of Pr3+ ion-doped chalcogenide glasses

In this work, Pr³⁺ ion-doped Ge₂₀Ga_15−xSb_xSe₆₅ (x = 0, 5, 10, in mol%), Ge₂₀Sb_15−yIn_ySe₆₅ (y = 5, 10, in mol%), Ge₂₀Ga_15−zIn_zSe₆₅ (z = 0, 5, 10, in mol%), and Ge₂₀Ga₅Sb₁₀Se₆₀I₅ glasses were prepared. The structural units, thermal properties, and optical properties of these glasses were analyzed. In addition, a comprehensive comparison study of the effects of metal ions (Sb, Ga, and In), S/Se ratio, and I content on the mid-infrared (MIR) luminescence of Pr³⁺ ions was conducted. Under a 1.55-μm laser pump, 0.2 mol% of Pr³⁺ ion-doped chalcogenide glasses performed strong photoluminescence in the wavelength range of 3.5-5.5 μm. Results indicated that the Sb-containing glass performed the strongest emission intensity among the studied glasses. Moreover, halogen element I can reduce the phonon energy of the matrix, which is beneficial to the luminescence of Pr³⁺ ions and provide significant possibilities for developing MIR lasers and amplifiers.     

Evolution of microstructure,optical, and magnetic properties in multiferroic CuFe1-xSnxO2 (x = 0–0.05)

Evolution of the microstructure, optical, and magnetic properties have been investigated systematically in multiferroic CuFe_1-xSn_xO₂ (x?=?0–0.05) ceramics. Substitution of Sn⁴⁺ for Fe³⁺ results in expansion of CuFeO₂ lattice, and reduces the density of the material, but the metal oxidation states are unchanged. Observation of the optical properties shows that the value of the direct optical band gap (E_g) decreases with increasing Sn doping level, and that the CuFe_1-xSn_xO₂ (x?=?0–0.04) series with values >?3.1?eV. Magnetic susceptibility measurements show that Sn⁴⁺ doping decreases the Curie-Weiss temperature, i.e. weakens the strength of the antiferromagnetic interaction between high-spin Fe³⁺ ions, but does not affect the stability of the antiferromagnetic phase, and all samples undergo successive magnetic transitions at about T_N1 =?15?K and T_N2 =?11?K. However, magnetization curves show that changes occur in the magnetic interactions and both ferromagnetism and antiferromagnetism co-exist in the Sn⁴⁺-doped samples. The maximum value of the saturation magnetization of 1.8?emu·g^?1 was observed for the x?=?0.03 sample in a 2.5?kOe field. The changes in the magnetic behavior are closely related to the lattice distortion and charge compensation, which are discussed in detail in this work.     

Co-precipitation synthesis,band modulation and improved visible-light-driven photocatalysis of Te4+/Ti4+-codoped Bi3Nb17O47

Bismuth niobate semiconductors are of considerable interest in both contaminant degradation and H₂-generation. However, the wide band gap strictly limits the optical absorption in visible-light wavelength. In this work, a new niobate semiconductor Bi₃Nb₁₇O₄₇ was prepared with co-precipitation synthesis. To modify the band structure, Te⁴⁺-, Ti⁴⁺-, and Te⁴⁺/Ti⁴⁺-doping were conducted in Bi₃Nb₁₇O₄₇ lattices. Rietveld refinements were used to investigate the crystal phase and structure. The UV–vis absorption measurements concluded that Te⁴⁺-, Ti⁴⁺- doping could greatly modify the band energy of Bi₃Nb₁₇O₄₇. The Te⁴⁺/Ti⁴⁺-doped sample could harvest more visible light in the longer-wavelength region being favorable for photocatalysis performances. This was verified by RhB photodegradation tests under the visible-light irradiation (λ > 420 nm). To discuss the photocatalytic mechanisms, XPS and impedance spectra were measured. The improved photocatalysis was related to the microstructure changes, charge carrier dynamics, oxygen vacancies, and redox couples of multivalent ions. The present work provides a valid route to modify the band structure and to improve the photocatalysis abilities via impurity ions Te⁴⁺/Ti⁴⁺-doping in bismuth niobate semiconductors.     

The influence of chloride ions on the kinetics of iron dissolution

The anodic dissolution of pure iron was studied in oxygen-free solutions at high concentrations of chloride and hydrogen ions at 25°C under potentiostatic steady-state conditions. In the range c_H⁺ ? 1 M the following kinetic data were obtained: Tafel slope b₊ ? +100 mV, electrochemical reaction order related to C_H⁺, n_+.H⁺ = +1·1, and electrochemical reaction order related to the chloride ion concentration, n_+,Cl^? = +0·6. These values cannot be correlated to the currently proposed mechanisms of iron dissolution, another mechanism is suggested for the described conditions. The correlations to known mechanisms are discussed.     

Synthesis and characterization of yttrium iron garnet nanoparticles doped with cobalt

In this work, we have synthesized and characterized yttrium iron garnet nanoparticles doped with cobalt. The X-ray diffraction data showed a single phase, belonging to the cubic structure of Y₃Fe₅O₁₂. Rietveld refinement revealed variation of the angles and interionic distances (Fe³⁺(a)-O^2-Y³⁺(c) and Fe³⁺(d)-O^2--Y³⁺(c) when Fe³⁺ ions are replaced by Co³⁺ ions in the tetrahedral (d) and octahedral (a) sites of YIG. In addition, the lattice parameter a, decreases from 12.3846?Å to 12.3830?Å with the increasing of cobalt concentration. The analysis by Infrared and Raman spectroscopies has shown a slight stretching at lower wave numbers as the dopant concentration increased. The magnetic measurements confirm the substitution of Fe³⁺ by Co³⁺ in the a-sites and d-sites with the reduction of the saturation magnetization from 26.63?emu/g to 24.92?emu/g, for 0.000?≤?y?≤?0.030. Changes in the coercive field varying the dopant concentration were related to the particle size and pinning centers existence.     

THERMODYNAMIC STUDY OF M3+/H+ EXCHANGE SYSTEMS ON TITANIUM ANTIMONATE CATION EXCHANGER

ABSTRACT

Selectivity coefficients K_H ^M for trivalent metal ions / hydrogen ions (M³⁺/H⁺) exchanges on titanium antimonate cation exchanger (TiSbA) have been determined for group 13 metals (Al³⁺, Ga³⁺, and In³⁺) and rare earth metals (La³⁺, Nd³⁺, Eu³⁺, Yb³⁺, and Y³⁺) ions by batch equilibration at 30, 45, and 60 ^°c in nitric acid media. Kielland plots (logK_H ^M vs. the fractional exchange X¯_M) for these exchange systems have been analyzed and found to show a break point at X¯_M=0.005-0.01. This behavior can be interpreted assuming a two-site model. A site available at infinitesimal X¯_M value has a large steric effect. The selectivity in this site increased in the order: Al³⁺ < Ga³⁺ < In³⁺ for group 13 metal ions and Y³⁺ < Yb³⁺ < Eu³⁺ < Nd³⁺ < La³⁺ for rare earth metal ions in the X¯M<0.02 region at 30^°C. The amounts of Ga³⁺ exchanged by TiSbA increased with a rise in temperature. The selectivity of group 13 metal ions changed to: AI³⁺ < In³⁺ < Ga³⁺ at 60^°C. On the other hand, the selectivity order for rare earth metal ions was independent of temperature. The hypothetical thermodynamic data (ΔG^o _ideal, ΔH^o _ideal and ΔS^o _ideal) at 25^°C were evaluated.     

Achieving highly efficient far-red emission from luminescence-ignorable Ca2MgTeO6:Mn4+ to Ca2-zLnzMgTe1-yWyO6:Mn4+ (Ln = La,Y, Gd) phosphors via solid solution and impurity doping strategies

The Mn⁴⁺-doped Ca2MgTeO6 (CMTO) far-red emitting phosphors with double perovskite-type structure were successfully synthesized. Upon near-ultraviolet (n-UV, 300 nm) light excitation, the as-prepared phosphors showed far-red light at 700 nm attributed to the ²E_g→⁴A_2g transition of Mn⁴⁺ ion. The doping concentration of the CMTO:xMn⁴⁺ samples was optimized to be 0.8 mol%. The relevant mechanism of concentration quenching was demonstrated as the dipole-dipole interaction. Furthermore, solid solution and impurity doping strategies were adopted to improve the far-red emission of the luminescence-ignorable CMTO:Mn⁴⁺ phosphor. Series of Ca₂MgTe_(1−y)W_yO₆:0.8 mol%Mn⁴⁺ (y = 0–100 mol%) solid solution and Ca_2−zLn_zMgTe_0.6W_0.4O₆:Mn⁴⁺ (Ln = La, Y, and Gd, z = 10 mol%) phosphors were synthesized through the above two strategies. The luminescence intensity of the optimal Ca_1.9Gd_0.1MgTe_0.6W_0.4O₆:Mn⁴⁺ phosphor was 13.7 times that of the CMTO:Mn⁴⁺ phosphor and 2.51 times that of red commercial phosphor K₂SiF₆:Mn⁴⁺. Notably, both CMTO:Mn⁴⁺ and Ca_1.9Gd_0.1MgTe_0.6W_0.4O₆:Mn⁴⁺ phosphors exhibited remarkable thermal stability compared with most Mn⁴⁺-doped phosphors. Finally, the highly efficient Ca_1.9Gd_0.1MgTe_0.6W_0.4O₆:Mn⁴⁺ phosphor was successfully applied in fabricating the warm white light diode (w-LED). This working along both lines strategy exhibited great potential for luminescence optimization of Mn⁴⁺-doped oxide phosphors.