Magnetic properties of the mixed spinel Co1+xSnxFe2−2xO4

The structural and magnetic properties of the mixed spinel Co_1+xSn_xFe_2?2xO₄ system for 0.1≤x≤0.5 have been studied by means of X‐ray diffraction, magnetization, a.c. susceptibility and Mössbauer effect measurements. X‐ray intensity calculations indicate that Sn⁴⁺ ions occupy only octahedral (B) sites replacing Fe³⁺ ions and the added Co²⁺ ions substitute for A‐site Fe³⁺ ions. The lattice constants are determined and the applicability of Vegard's law has been tested. The Mössbauer spectra at 300 K have been fitted with two sextets in the ferrimagnetic state corresponding to Fe³⁺ at tetrahedral (A) and octahedral (B) sites for x≤0.4. The Mössbauer intensity data show that Sn possesses a preference for the B‐site of the spinel. As expected, the hyperfine field and Curie temperature determined from a.c. susceptibility decreases with increasing Sn content. The variation of the saturation magnetic moment per formula unit measured at 77 and 300 K with Sn content is satisfactorily explained on the basis of Néel's collinear spin ordering model for x=0.1–0.4.     

Fluorinated Eu‐Doped SnO2 Nanostructures with Simultaneous Phase and Shape Control and Improved Photoluminescence

Fluorinated Eu‐doped SnO₂ nanostructures with tunable morphology (shuttle‐like and ring‐like) are prepared by a hydrothermal method, using NaF as the morphology controlling agent. X‐ray diffraction, field‐emission scanning electron microscopy, high‐resolution transmission electron microscopy, X‐ray photoelectron spectroscopy, and energy dispersive spectroscopy are used to characterize their phase, shape, lattice structure, composition, and element distribution. The data suggest that Eu³⁺ ions are uniformly embedded into SnO₂ nanocrystallites either through substitution of Sn⁴⁺ ions or through formation of Eu‐F bonds, allowing for high‐level Eu³⁺ doping. Photoluminescence features such as transition intensity ratios and Stark splitting indicate diverse localization of Eu³⁺ ions in the SnO₂ nanoparticles, either in the crystalline lattice or in the grain boundaries. Due to formation of Eu‐F and Sn‐F bonds, the fluorinated surface of SnO₂ nanocrystallites efficiently inhibits the hydroxyl quenching effect, which accounts for their improved photoluminescence intensity.     

Cu(In,Sn)Se2 thin films for absorption of energy from infrared radiation

In this study, we sought to lower the bandgap of thin film solar cells by replacing the Ga used in the absorber layer of Cu(In,Ga)Se₂ with Sn (bandgap of 0.07?eV) to form Cu(In,Sn)Se₂. The proposed scheme was shown to reduce the bandgap of the absorber layer from 1.0?eV to 0.88?eV. Sn films of various thicknesses were deposited using precursors of Sn–In–Cu metal in order to study the effects of Sn/(In?+?Sn) ratio (SIR) on the structure of the material and photoelectrical characteristics of the Cu(In,Sn)Se₂ absorber layer. Experiment results revealed that a higher SIR following selenization increased the grain size and surface roughness of the absorber layer. It increased the quantity of secondary phases of SnSe₂ and Cu₂SnSe₃ and improved the distribution of Cu and In in the absorber layer. A higher SIR was also shown to increase electron mobility while decreasing carrier concentration and conductivity. When SIR≧0.25, the replacement of In³⁺ with Sn⁴⁺in the Cu⁺ vacancies decreased the electron strength of In. We speculate that an increase in SIR caused a relative increase in the quantity of Sn²⁺ compared to Sn⁴⁺, thereby increasing the electron strength of Sn and switching the absorber layer from a p-type to an n-type semiconductor.     

Study on ferroelectric polarization induced resistive switching characteristics of neodymium-doped bismuth ferrite thin films for random access memory applications

The present work reports on resistive switching (RS) characteristics of Neodymium (Nd)-doped bismuth ferrite (BFO) layers. The Nd (2–10 at%) doped BFO thin film layers were deposited using a spray pyrolysis method. The structural analysis reveals that a higher Nd doping concentration in BFO leads to significant distortion of the prepared Nd:BFO thin films from rhombohedral to tetragonal characteristics. The morphological analysis shows that all the deposited Nd:BFO thin films have regularly arranged grains. The X-ray photoelectron spectroscopy (XPS) analysis reveals that the prepared Nd:BFO thin films have a higher Fe ³⁺/Fe ²⁺ratio and less oxygen vacancy (V_O) defects which enriches the ferroelectric characteristics in Nd:BFO layers. The polarization-electric field (P-E) and RS characteristics of the fabricated Nd:BFO-based RS device were examined. It was observed that the Nd (7 at%) doped BFO RS device shows large remnant polarization (P _r) of 0.21 μC/cm² and stable RS characteristics.     

Magneto-crystalline properties of BaFe12−2x M x Sn x O19 (M = Sn, Ni, Zn) ferrite powders

BaFe_12?2x M _x Sn _x O₁₉ compounds, where M?=?Sn²⁺, Ni²⁺ or Zn²⁺ ions, were synthesized by mechanical milling and partially by citrate precursor methods. Analysis of magneto-crystalline structure has been carried out by Mössbauer spectroscopy. The Sn⁴⁺ ions replace Fe³⁺ ions on 2b and slightly on 2a?+?4f₁ sites, Zn²⁺ ions strongly prefer 4f₁ sites, Sn²⁺ ions prefer 4f₁ sites too and Ni²⁺ ions occupy 4f₂ and 12k or 2a sites. The magnetic properties were evaluated by the vibrating sample magnetometry and the thermomagnetic analysis. A large variation of the intrinsic coercivity H _c (330 to 78 kA/m) and of temperature coefficient of coercivity of ΔH _c /Δ? (0.39 to 0.22 kA/m°C) were achieved as a function of the (Zn–Sn) and (Sn–Sn) substitutions, respectively. The Curie temperature T _c decreased with the (Ni–Sn) substitution from 447 to 399°C.     

Insight into structural,mechanical, electronic and thermodynamic properties of intermetallic phases in Zr–Sn system from first-principles calculations

The structural, phase stabilities, mechanical, electronic and thermodynamic properties of intermetallic phases in Zr–Sn system are investigated by using first-principles method. The equilibrium lattice constants, enthalpy of formation (ΔH^form) and elastic constants are obtained and compared with available experimental and theoretical data. The configuration of Zr₄Sn is measured with reasonable precision. The ΔH^form of five hypothetical structures are obtained in order to find possible metastable phase for Zr–Sn system. The mechanical properties, including bulk modulus, shear modulus, Young's modulus and Poisson's ratio, are calculated by Voigt–Reuss–Hill approximation and the Zr₅Sn₄ and Zr₅Sn₃ show excellent mechanical properties. The electronic density of states for Zr₅Sn₄, Zr₅Sn₃ and cP8-Zr₃Sn are calculated to further investigate the stability of intermetallic compounds. Through the quasi-harmonic Debye model, the Debye temperature, heat capacity and thermal expansion coefficient under temperature of 0–300 K and pressure of 0–50 GPa for Zr₅Sn₃ and Zr₅Sn₄ are deeply investigated.     

Low temperature CEMS of Sn-implanted SiO2

Conversion electron Mössbauer spectroscopy (CEMS) at room and low temperature has been used to study thin SiO₂ films implanted with Sn atoms and annealed at 900°C. This work focuses on the determination of the Debye temperature (θ _D) and Debye–Waller factors (f) of the Sn oxidized phases formed in this system. The Sn²⁺ oxidation state is the predominant one, even if a small percentage of the Sn atoms is in the Sn⁴⁺ oxidation state. The real Sn-oxides fractions are calculated by normalizing the resonant areas to the f values, as calculated from the temperature dependence of the related resonant areas within a Debye model. The Sn⁴⁺ oxidation state, possibly related to Sn atoms close to the SiO₂ surface, represents less than 20% of the Sn atoms. For the Sn²⁺ oxidation state, two different electronics configurations a and b, having different Debye temperature and hyperfine parameters are identified. The component a, with a lower θ _D (137 K), is the predominant one and might be related to small (2–3 nm) amorphous SnO _x clusters in the SiO₂ matrix. The component b could be related to substitutional Sn atoms in the SiO₂ network forming a local Sn environment similar to the SnO amorphous compound.     

Nanostructured BaTi1-xSnxO3 ferroelectric materials for electrocaloric applications and energy performance

Nanostructured BaTi_1-xSn_xO₃ (x = 0, 0.05 & 0.075) were successfully synthesized using the modified Pechini processing method. The phase purity and symmetry were examined by X-ray diffraction and Raman spectroscopy. Tetragonal symmetry was obtained for BaTiO₃ (BT) while orthorhombic symmetry for Sn doped BT. BT exhibits an up-shift of the Curie temperature towards high temperatures (T_C = 139 °C). In contrast, a down-shift was recorded for Sn doped BT. Then, indirect electrocaloric (EC) adiabatic temperature change ΔT and the energy storage performances were determined based on ferroelectric hysteresis loops. Interestingly, large EC responsivity of ΔT/ΔE = 0.81 × 10⁻⁶ K m/V was obtained for the BT accompanied with a moderate stored energy of 23 mJ/cm³ but with a high energy efficiency of 67%. The incorporation of Sn in BT was found to broaden the EC responsivity and to improve the energy efficiency up to 90%, recorded for the 5% Sn doped BT.     

Effects of Sn doping on the morphology,structure, and electrical property of In2O3 nanofiber networks

This paper studies the effect of Sn doping on the morphological, structural, and electrical properties of the Sn-doping In₂O₃ nanofiber networks. In₂O₃-based nanofibers with various relative concentration of Sn precursor (0–20 mol%) were fabricated through the electrospinning method. Scanning electron microscopy observations show that, depending on the relative concentration of SnCl₄ in the starting materials, the doped nanofibers with different morphologies, from smooth to corn-like and then to accidented, are fabricated. Transmission electron microscopy and X-ray diffraction analyses reveal that the Sn dopants influence the growth direction of seeds, resulting in doped nanoparticles having diverse shapes and sizes, which are critical for the formation of doped nanofiber with different morphology. From these nanofiber networks, we fabricated several thin sheets to characterize the effect of Sn concentration on the electrical resistivity. The resistivity of thin sheets decreased significantly before the doping concentration up to 12.5 mol%, and then increased slightly at a larger addition. This work will assist further understanding the formation of Sn-doped In₂O₃ nanofibers and is expected to be extended to other transparent conductive oxides.     

Effect of non-magnetic doping on leakage and magnetic properties of BiFeO3 thin films

In this paper, we show that the leakage current properties of BiFeO₃ (BFO) thin films have been greatly improved by Zr-doping. In contrast, the magnetic properties of Zr-doped BFO films are affected as a weak ferromagnetism. Beyond the double-exchange interactions arising from the creation of Fe²⁺, we propose another simple model considering the replacement of the magnetically active Fe³⁺, time to time, by a non-active Zr⁴⁺, which is expected to induce a local ferromagnetic coupling rather than an antiferromagnetic one.     

Asymmetry in electrical properties of Al‐doped TiO2 film with respect to bias voltage

The energy diagram of RuO₂/Al‐doped TiO₂/RuO₂ structures was estimated from the capacitance–voltage and leakage current density–voltage curves. The Al‐doping profile in TiO₂ film was varied by changing position of the atomic layer deposition cycle of Al₂O₃ during the atomic layer deposition of 9 nm‐thick TiO₂ film. The interface between the TiO₂ film and the RuO₂ electrode containing Al‐doping layer showed a higher Schottky barrier by 0.1 eV compared with the opposite interface without the doping layer. The evolution of various leakage current profiles upon increasing the bias with opposite polarity could be well explained by the asymmetric Schottky barrier. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

119Sn Mössbauer study of nickel–tin anodes for rechargeable lithium-ion batteries

¹¹⁹Sn Mössbauer spectrometry has been carried out on Ni–Sn alloys (Ni₃Sn LT, Ni₃Sn₂ LT and Ni₃Sn₄) and combined with ab initio calculations. Lithium insertion/extraction mechanisms of the most interesting compound (Ni₃Sn₄) have been studied from ¹¹⁹Sn Mössbauer measurements. The first discharge shows a plateau close to 0.0 V, which can be attributed to the formation of the Li₇Sn₂ alloy.     

A tin-119 Mössbaer spectroscopic study of tin-doped niobium titanium phosphate

¹¹⁹Sn Mössbauer spectroscopy shows that the reaction of metallic tin with niobium titanium phosphate, NbTiP₃O₁₂, results in the accommodation of Sn²⁺ in two types of sites within channels in the NbTiP₃O₁₂ structure. The Sn²⁺ absorptions are characterised by highly positive chemical isomer shifts which decrease as increasing concentrations of Sn²⁺ are incorporated within the NbTiP₃O₁₂ structure. At very high tin concentrations the Mössbauer spectra show the presence of some unreacted elemental tin. The¹¹⁹Sn Mössbauer data are endorsed by X-ray powder diffraction data and are discussed in terms of the incorporation of highly ionic Sn²⁺ species.     

High-pressure Mössbauer study of the Curie temperatures and transferred hyperfine fields at 151Eu and substitutional 119Sn in EuS and EuSe

Changes with pressures up to 55 kbar of the Curie temperatures and the ¹⁵¹Eu and ¹¹⁹Sn hyperfine parameters were investigated in the europium monochalcogenides EuS and EuSe doped with small amounts of substitutional Sn²⁺. In both (Eu_1-xSn_x) S and (Eu_1-xSn_x) Se with 0.01 ≤x ≤ 0.05, the observed strong increase of T_c is correlated w ith a strong increase of the transferred hyperfine fields. EuSe is found to order ferromagnetically above 14 kbar.     

四价锡离子导体——锡蒙脱石

在实验室制得一种四价阳离子导体——锡蒙脱石。样品的穆斯堡尔谱证明迁移锡离子的价态为四价锡离子。锡蒙脱石的电子电导率和交流电导率分别为5.1×10^-7和1.5×10^-4S/cm。应用于锡锰电池中φ13mm×3mm的片状电池得到1.2V的开路电压和5mA的短路电流。 关键词：     

Significantly reduced leakage currents in organic thin film transistors with Mn‐doped Bi2Ti2O7 high‐k gate dielectrics

We report the fabrication of organic thin‐film transistors (OTFTs) with high‐k gate dielectrics of Mn‐doped Bi₂Ti₂O₇ (BTO) films. 3% Mn‐doped BTO films deposited on polymer substrates by pulsed laser deposition at room temperature exhibit low leakage currents of 2.1 × 10^–8 A/cm² at an applied electric field of 0.3 MV/cm, while undoped BTO films show much higher leakage currents of 4.3 × 10^–4 A/cm². Mn doping effectively reduces the number of oxygen vacancies in the films and improves the electrical properties. Low operation voltage and significantly reduced leakage currents are demonstrated in pentacene‐based OTFTs with the Mn‐doped BTO gate dielectrics. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Hybrid density functional study of optically active Er3+ centers in GaN

Understanding the luminescence of GaN doped with erbium (Er) requires a detailed knowledge of the interaction between the rare‐earth dopant and the nitride host, including intrinsic defects and other impurities that may be present in the host material. We address this problem through a first‐principles hybrid density functional study of the structure, energetics, and transition levels of the Er impurity and its complexes with N and Ga vacancies, substitutional C and O impurities, and H interstitials in wurtzite GaN. We find that, in the interior of the material, Er_Ga is the dominant Er³⁺ center with a formation energy of 1.55 eV, Er_Ga–V_N possesses a deep donor level at 0.61 eV which can assist in the transfer of energy to the 4f ‐electron core. Multiple optically active Er³⁺ centers are possible in Er‐doped GaN. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Phase transformation in Ni–Mn–Sn ferromagnetic shape memory alloy thin films induced by dense ionization

The effects of 200 MeV Au ions irradiation on the structural and magnetic properties of Ni–Mn–Sn ferromagnetic shape memory alloy (FSMA) thin films have been systematically investigated. In order to understand the role of initial microstructure and phase of the film with respect to high energy irradiation, the two types of Ni–Mn–Sn FSMA films having different phases at room temperature were irradiated, one in martensite phase (Ni_58.9Mn_28.0Sn_13.1) and other in austenite phase (Ni₅₀Mn_35.6Sn_14.4). Transmission electron microscope (TEM) and scanning electron microscope (SEM) images along with the diffraction patterns of X-rays and electrons confirm that martensite phase transforms to austenite phase at a fluence of 6×10¹² ions/cm² and a complete amorphization occurs at a fluence of 3×10¹³ ions/cm², whereas ion irradiation has a minimal effect on the austenitic structure (Ni₅₀Mn_35.6Sn_14.4). Thermo-magnetic measurements also support the above mentioned behaviour of Ni–Mn–Sn FSMA films with increasing fluence of 200 MeV Au ions. The results are explained on the basis of thermal spike model considering the core and halo regions of ion tracks in FSMA materials.     

Modification in structure of La and Nd co‐doped epitaxial BiFeO3 thin films probed by micro Raman spectroscopy

The influence of La and Nd co‐substitution on structure, electric and magnetic properties of epitaxial thin films of BiFeO₃ (BFO) was examined. We demonstrate structural phase transition in co‐doped La and Nd BFO thin films using Raman spectroscopy. Based on group theoretical analysis of the number and symmetry of Raman lines, we provide strong experimental evidence that the structure has been changed from rhombohedral to monoclinic due to co‐doping in BFO. The change in structure was also reflected in morphology of these films. Room temperature magnetic hysteresis curves showed that doped films exhibit enhanced ferromagnetic properties with remnant magnetization of ~10 emu/cm³ and coercive field of 1.2 kOe. The enhanced magnetic properties highlight the potential applications of doped BLNFO thin film for smart devices. Copyright © 2015 John Wiley & Sons, Ltd.