The presence of fivefold germanium as a possible transitional phase in the iron–lead–germanate glass system

Glasses in the system xFe₂O₃·(100 − x)[7GeO₂·3PbO] with 0 ≤ x ≤ 60 mol% have been prepared from melt quenching method. In this article, we investigated changes in germanium coordination number in iron–lead–germanate glasses through molar volume analysis, measurements of densities, investigations of FTIR, and UV–VIS spectroscopy. The observations present in these mechanisms show that the lead ions have an affinity pronounced toward [GeO₅] and [FeO₄] structural units with non-bridging oxygens. The excess of oxygen can be supported into the glass network by the formation of [FeO₆] structural units and the apparition of the germanate anomaly. At higher content of iron (III) oxide, the anomaly behavior of the germanium is due to the formations of [FeO₆] structural units. Our results show that the presence of fivefold germanium as a possible transitional phase from four to sixfold germanium it is necessary for the formation of the [FeO₆] structural units and the apparition of the Fe₂O₃ crystalline phase. Pb⁺² ions with 6s² configuration show strong absorption in the ultraviolet due to parity allowed s²-sp transition.     

Crystallographic and magnetic properties of Fe-doped SnO<Subscript>2</Subscript> nanopowders obtained by a sol–gel method

We prepared Sn_1?x Fe _x O₂ (x = 0, 0.03, 0.05, 0.10, and 1.0) nanoparticles by the polymeric precursor method based on the modified Pechini process. Two types of starting reactants for both tin and iron were explored: Sn(II)/Fe(II) and Sn(IV)/Fe(III) precursors. Thermogravimetric analysis revealed that the precursor powders prepared from Sn(IV) have higher excess in ethylene glycol in comparison to precursor samples prepared from Sn(II). XRD patterns for those samples prepared from Sn(IV) and Fe(III) were adequately fitted by introducing only the cassiterite phase of SnO₂. Micro-Raman spectra also support these findings, and additionally it is found that the presence of iron broadened and reduced the intensities of the principal bands. ¹¹⁹Sn Mössbauer spectra indicated only the presence of Sn⁴⁺, whereas RT ⁵⁷Fe Mössbauer spectra suggested the presence of two Fe³⁺ sites located at different distorted sites. On the other hand, micro-Raman and ⁵⁷Mössbauer spectrometry showed the formation of hematite as impurity phase for those samples with iron concentrations above ~5 at.%, prepared from Fe(II) and Sn(II) precursors. In addition, their XRD patterns revealed larger average grain sizes for the cassiterite phase of SnO₂ in comparison to those samples prepared from Sn(IV) and Fe(III).     

IR study of Pb-Sr titanate borosilicate glasses

The infrared spectra (IR) of various glass compositions in the glass system, [(Pb _x Sr_1−x )O·TiO₂]-[2SiO₂·B₂O₃]-[BaO·K₂O]-[La₂O₃], were recorded over a continuous spectral range (400–4000 cm⁻¹) to study their structure systematically. IR spectrum of each glass composition shows a number of absorption bands. These bands are strongly influenced by the increasing substitution of SrO for PbO. Various bands shift with composition. Absorption peaks occur due to the vibrational mode of the borate network in these glasses. The vibrational modes of the borate network are seen to be mainly due to the asymmetric stretching relaxation of the B-O bond of trigonal BO₃ units. More splitting is observed in strontium-rich composition.     

Conduction mechanism in Sn4+ substituted copper ferrite

Thermoelectric power (α) and electrical resistivity (ρ) are reported for the system Cu_1+x Sn _x Fe_2−2x O₄ (wherex=0·05, 0·1, 0·15, 0·2 and 0·3) from room temperature to 800 K. The compositions withx=0·05 and 0·2 exhibitn-type conduction while the compositions withx=0·1 and 0·15 showp- ton-type conduction change after 423 K. The conduction at low temperature (i.e. < 400 K) is due to impurities, while at higher temperature (i.e. > 400 K), it is due to polaron. Hopping conduction phenomenon for the present system has been explained on the basis of localized model of electrons. Additional localization may arise due to Sn⁴⁺ + Fe²⁺ stable pairs at B-site and Cu¹⁺ + Fe³⁺ pair at A-site.     

Structural and magnetic properties of strontium–borate glasses containing iron ions

Glasses of the xFe₂O₃·(100 − x)[B₂O₃·SrO] system, with 0 ≤ x ≤ 30 mol%, were studied by EPR and magnetic susceptibility measurements. EPR spectroscopy and magnetic susceptibility measurements show that the Fe³⁺ ions are localized in sites of distorted octahedral symmetry and in clustered formations containing both Fe³⁺ and Fe²⁺ ions. Dipolar and superexchange interactions involving iron ions were revealed depending on the iron content of the sample.     

Structural investigation of xFe2O3 · (100 − x)[P2O5 · TeO2] glass system by FT-IR study and EPR spectroscopy

Glasses from xFe₂O₃ · (100 − x)[P₂O₅ · TeO₂] system, with 0 ≤ x ≤ 50 mol%, were investigated by X-ray diffraction, FT-IR and EPR spectroscopies. The XRD patterns show a vitreous state of studied samples for x ≤ 35 mol% Fe₂O₃. The FT-IR spectrum of the P₂O₅ · TeO₂ glass matrix reveals a structure formed from PO₄, TeO₄ and TeO₃ units. The addition and the increasing of Fe₂O₃ content modify progressively the structure of the glass matrix. The local structure in the investigated glasses was revealed by means of EPR using Fe³⁺ (3d⁵; ⁶S_5/2) ions as paramagnetic probes. The EPR spectra present two resonance absorption lines characteristic to Fe³⁺ ions centred at g_eff ≈ 2.0, for 0.5 ≤ x ≤ 35 mol% and g_eff ≈ 4.3, for 0.5 ≤ x ≤ 5 mol%. The variation of the EPR parameters, the intensity and line-width of these absorption lines, with iron ions composition has been followed.     

Thermodynamic potentials, diagram of state, and phase transitions of tin on shock compression

The isochoric-isothermal potentials are constructed for white tin Sn_Β and two high-pressure phases of this metal, Sn_γ and Sn_Σ. Based on these and previously obtained similar data for tin melt Sn_l, a phase diagram of tin is constructed in the ranges of pressure from zero to 120 GPa and temperature from 300 to 7000 K; the behavior of the shock adiabat of tin is then treated in the vicinity of its intersection with the obtained equilibrium lines of four phases.     

Effect of Mn doping on the structural,morphological, optical and magnetic properties of indium tin oxide films

We report on the preparation and characterization of high purity manganese (3–9 wt.%) doped indium tin oxide (ITO, In:Sn = 90:10) films deposited by sol–gel mediated dip coating. X-ray diffraction and selected area electron diffraction showed high phase purity cubic In₂O₃ and indicated a contraction of the lattice with Mn doping. High-resolution transmission electron microscopy depicted a uniform distribution of ∼20 nm sized independent particles and particle induced x-ray emission studies confirmed the actual Mn ion concentration. UV-Vis diffuse reflectance measurements showed band gap energy of 3.75 eV and a high degree of optical transparency (90%) in the 100–500 nm thick ITO films. X-ray photoelectron spectroscopy core level binding energies for In 3d_5/2 (443.6 eV), Sn 3d_5/2 (485.6 eV) and Mn 2p_3/2 (640.2 eV) indicated the In³⁺, Sn⁴⁺ and Mn²⁺ oxidation states. Magnetic hysteresis loops recorded at 300 K yield a coercivity H_c ∼ 80 Oe and saturation magnetization M_s ∼ 0.39 μ_B/Mn²⁺ ion. High-temperature magnetometry showed a Curie temperature T _c > 600 K for the 3.2% Mn doped ITO film.     

Temperature dependence of the frequency of two-electron exchange between impurity negative-U tin centers in lead sulfide

Fast two-electron exchange between neutral Sn²⁺ and doubly ionized Sn⁴⁺ impurity negative-U tin centers in partially compensated Pb_0.98Sn_0.02Na_0.01Tl_0.01S solid solutions has been found by emission Mössbauer spectroscopy on ^119mmSn(^119mSn) isotope; the lifetime of the Sn²⁺ and Sn⁴⁺ states changes from ～6 × 10^?4 to ～8 × 10^?9 s with a change in temperature from 295 to 900 K.     

Microwave synthesis and physical characterization of tin(II) phosphate glasses

Tin phosphate glasses in the SnO–P₂O₅ binary diagram have been prepared by using a domestic microwave-heating device. Microwaves provide an extremely facile and automatically temperature-controlled route to the synthesis of glasses due to the specific dielectric properties of each chemical composition. Typical melting time is no longer than 10 min, limiting the oxidation of Sn²⁺ and the melt can be quenched into glass. The glass transition temperature increases with the SnO content confirming the depolymerization of the vitreous network, as expected by the relative fraction of the different Q ⁿ structural units deduced from NMR experiments. Concerning the mechanical properties, the Vickers hardness and the fracture toughness decrease while the thermal expansion coefficient and the different elastic moduli remain constants. These results confirm that those characteristics are not very sensible to structural considerations. On the contrary, the chemical durability of Sn₂P₂O₇, determined from the weight loss method, is 300 times higher than that of Sn(PO₃)₂. Furthermore, Sn₂P₂O₇ is the only glass composition that exhibits a devitrification phenomenon leading to the low-temperature phase of the crystalline tin(II) pyrophosphate.     

Magnetic order in tin-doped thiospinels

The tin-doped sulphur-containing compound of composition Fe_1.05Cr_1.90Sn_0.05S₄, in which tin is located on the octahedral sites as Sn(IV) in the spinel-related structure, has been examined by ¹¹⁹Sn Mössbauer spectroscopy. The data complement results obtained by ⁵⁷Fe Mössbauer spectroscopy and show that tin doping increases the magnetic ordering temperature of pure FeCr₂S₄. These results are compared with the data obtained on tin-doped CuCr₂X₄ compounds (X = O, S, Se).     

cis-1,3,4,6-Tetranitrooctahydroimidazo-[4,5-d]imidazole (BCHMX), its properties and initiation reactivity

Pre-treatment of simulated industrial wastewaters (SIM1, SIM2 and SIM3) containing organic and inorganic compounds (1,2-dichloroethane, sodium formate, sodium hydrogen carbonate, sodium carbonate and sodium chloride) by oxidative degradation using homogeneous Fenton type processes (Fe²⁺/H₂O₂ and Fe³⁺/H₂O₂) has been evaluated. The effects of initial Fe²⁺ and Fe³⁺ concentrations, [Fe^2+/3+], type of iron salt (ferrous sulfate vs. ferric chloride), initial hydrogen peroxide concentration, [H₂O₂], on mineralization extent, i.e., total organic content (TOC) removal, were studied. Response surface methodology (RSM), particularly Box–Behnken design (BBD) was used as modelling tool, and obtained predictive function was used to optimize the overall process by the means of desirability function approach (DFA). Up to 94% of initial TOC was removed after 120 min. Ferrous sulfate was found to be the most appropriate reagent, and the optimal doses of Fe²⁺ and H₂O₂ for reducing the pollutant content, in terms of final TOC and sludge production were assessed.     

A comparative study of different solvothermal methods for the synthesis of Sn<Superscript>2+</Superscript>-doped BaTiO<Subscript>3</Subscript> powders and their dielectric properties

Ternary oxides containing Sn²⁺ are rare and difficult to prepare by the conventional solid state reactions due to the disproportionation of Sn²⁺ to Sn⁴⁺ and Sn at high temperatures. In this article, Sn²⁺-doped barium titanate, Ba_1−x Sn _x TiO₃ (x = 0.00, 0.02, 0.05, and 0.10) nanopowders were successfully synthesized at a moderate temperature by a microwave-assisted solvothermal reaction (MSR) and a solvothermal reaction with rolling (SRR). The powders obtained using the MSR and SRR consisted of nanoparticles of 20–50 nm and 100–120 nm in diameter, respectively. The dielectric constant of the sample increased by doping with a small amount of Sn²⁺ (x ≤ 0.05), but decreased by doping in excess amounts of it.     

Effect of secondary heat treatment on the spectroscopic properties of Na<Subscript>2</Subscript>O-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>-P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

We have studied the optical absorption and luminescence spectra of 45Na₂O · xNb₂O₅ · (55 − x)P₂O₅ glasses containing 5, 10, 20, 25, 30, and 35 mol % Nb₂O₅. The results indicate that the absorption band around 26000 cm⁻¹, responsible for the yellow color of the glasses, is due to the [Nb^(5+)--O⁻] center and disappears upon secondary heat treatment. Heat treatment of europium-doped glasses increases the concentration of Eu³⁺ centers in an asymmetric environment, which is accompanied by an increase in luminescence efficiency. The reason for this is that the Eu³⁺ ions are located outside the niobate subsystem of the glass matrix. The europium in the glasses studied acts as a protector ion.     

Understanding the electrochemical behavior of Sn(II) in choline chloride-ethylene glycol deep eutectic solvent for tin powders preparation

Tin is one of the vital substances in the material and chemical industry. Deep eutectic solvent (DES) possesses excellent physicochemical properties for metal preparation. In this study, the electrochemical behavior of Sn(II) and metallic tin preparation in choline chloride-ethylene glycol (ChCl-EG) DES were investigated. Linear sweep voltammetry is carried out to study the effects of substrate material (Ni, Cu, Pt, C, Fe, Al, W, glassy carbon (GC) and Ti), temperature (313–353 K) and SnCl₂ concentration (10–100 mM) on the electrochemical behavior of Sn(II)/Sn. Results demonstrate that metallic tin is easier to be prepared on the Ni electrode, and increasing temperature and SnCl₂ concentration both facilitate the reduction of Sn(II). Electrospray ionization mass spectrometry (ESI-MS) shows that the main form of Sn(II) is [SnCl₃]^-. Chronoamperometric tests indicate that with the increase of applied potential, the nucleation of Sn(II) on the nickel electrode becomes close to the instantaneous nucleation. Simultaneously, the nucleation rate and the number of active sites on the electrode surface increase significantly. Pure tin with a dendritic structure could be prepared with higher current efficiency of 96.4% and lower energy consumption of 320.5 kW·h·t^?1 without any additives. All these studies provide a fundamental basis for the preparation of tin powders in ChCl-EG DES.     

Crystal growth of sodium iron titanium bronze compounds under hydrothermal conditions

Single crystals of four types of oxides consisting of sodium iron and titanium were grown hydrothermally under reduced conditions starting with a mixture of TiO₂ (rutile) and metallic Fe powder in the ratio 5:1 (weight basis) at 650°C and 1000kg/cm² in 10m NaOH solution for different durations. Formation of single crystals having an orthorhombic cell was observed after one week. In longer runs under the same conditions the initial phase undergoes transformation to form crystals having hexagonal and orthorhombic cells and finally to monoclinic freaudenbergite (Na₂O·Fe₂O₃·7TiO₂). From Mössbauer and EPMA data, the common chemical formula for these new phases can be written as (Na_xFe²⁺_y) · [Ti_pFe²⁺_qFe_r³⁺O_2?δ]_n.     

Optical properties of aluminophosphate glasses containing silver, tin, and dysprosium

The spectroscopic properties of a Dy³⁺-doped aluminophosphate glass containing silver and tin were reported. Different oxidation and aggregation states of silver were obtained by varying silver concentration and glass thermal history. The addition of silver and tin at the lowest concentration studied results in Dy³⁺ ions emission under nonresonant UV excitation in connection with the appearance of an excitation band around 270 nm, which is associated to isolated Ag⁺ ions and twofold-coordinated Sn centers. The increase in silver and tin concentration leads to a broadening of aforementioned band and to the presence of charged silver dimers as evidenced by the appearance of an excitation band around 330 nm. The data indicated that light absorption might take place at ionic silver species and twofold-coordinated Sn centers, followed by energy transfer to Dy³⁺ ions. After heat treatment, ionic silver species were reduced to atomic Ag by tin with the subsequent formation of Ag nanoparticles (NPs) inside the dielectric host. A quenching effect in Dy³⁺ ions luminescence was shown with the presence of the Ag NPs, most notably for excitation of ⁶H_15/2 → ⁴F_9/2, ⁴I_15/2, ⁴G_11/2 transitions, which were in resonance with the dipole absorption mode of the particles. The silver NPs were believed to provide radiationless pathways for excitation energy loss in Dy³⁺ ions.     

FTIR and Raman spectroscopic investigation of some strontium–borate glasses doped with iron ions

Structural investigation of xFe₂O₃·(100 − x)[3B₂O₃·SrO] glass system, with 0 ≤ x ≤ 40 mol%, was performed by means of X-Ray diffraction (XRD), Fourier transform infrared (FTIR) and Raman spectroscopies. The purpose of this work was to investigate the structural changes that appear in the 3B₂O₃·SrO glass matrix with the addition and increasing of iron ions content. The XRD pattern for the prepared samples shows that vitreous phase is present only for x ≤ 40 mol%. For sample containing 50 mol% Fe₂O₃ was evidenced the presence of a unique crystalline phase, Fe₂O₃, embedded in an amorphous matrix. FTIR data show that BO₃ and BO₄ are the main structural units of the glass system and the iron ions are located in the network. The Raman spectrum of glass matrix indicates a structure with several borate groups (di-, meta-, pyro-borate, etc.). In higher concentrations the iron ions break the regulate glass network and determines the appearance of BO₄ isolated units.     

Classification of Lattice Defects in the Kesterite Cu2ZnSnS4 and Cu2ZnSnSe4 Earth‐Abundant Solar Cell Absorbers

The kesterite‐structured semiconductors Cu₂ZnSnS₄ and Cu₂ZnSnSe₄ are drawing considerable attention recently as the active layers in earth‐abundant low‐cost thin‐film solar cells. The additional number of elements in these quaternary compounds, relative to binary and ternary semiconductors, results in increased flexibility in the material properties. Conversely, a large variety of intrinsic lattice defects can also be formed, which have important influence on their optical and electrical properties, and hence their photovoltaic performance. Experimental identification of these defects is currently limited due to poor sample quality. Here recent theoretical research on defect formation and ionization in kesterite materials is reviewed based on new systematic calculations, and compared with the better studied chalcopyrite materials CuGaSe₂ and CuInSe₂. Four features are revealed and highlighted: (i) the strong phase‐competition between the kesterites and the coexisting secondary compounds; (ii) the intrinsic p‐type conductivity determined by the high population of acceptor Cu_Zn antisites and Cu vacancies, and their dependence on the Cu/(Zn+Sn) and Zn/Sn ratio; (iii) the role of charge‐compensated defect clusters such as [2Cu_Zn+Sn_Zn], [V_Cu+Zn_Cu] and [Zn_Sn+2Zn_Cu] and their contribution to non‐stoichiometry; (iv) the electron‐trapping effect of the abundant [2Cu_Zn+Sn_Zn] clusters, especially in Cu₂ZnSnS₄. The calculated properties explain the experimental observation that Cu poor and Zn rich conditions (Cu/(Zn+Sn) ≈ 0.8 and Zn/Sn ≈ 1.2) result in the highest solar cell efficiency, as well as suggesting an efficiency limitation in Cu₂ZnSn(S,Se)₄ cells when the S composition is high.     

Thermal expansion of silico-phosphate glasses with small additions of Fe2O3: EPR and dilatometric studies

Electron paramagnetic resonance (EPR) and dilatometric measurements in phosphosilicate glass have been made in order to elucidate an anomalous trend of the linear thermal expansion coefficientβ when Fe₂O₃ was added to the composition. The g≃2 and g_eff≃4.27 EPR lines were attributed, respectively, to undistorted and octahedrally coordinated Fe³⁺ ions, and to Fe³⁺ ions in low symmetry (rhombic) sites. The Fe³⁺ ion distribution in the network at different temperatures has been explained by a model of chemical insertion and it has been proved that the Fe³⁺ ions have two kinds of role as network modifiers. A relationship has also been found betweenβ and the amounts of Fe₂O₃ added in the range 0 to 12 wt %. It is with deep regret that we note the death of Professor G. L. Del Nero.