Structural disorder of ball-milled,nanosized, Fe-doped SnO<Subscript>2</Subscript>: X-ray diffraction and Mössbauer spectroscopy characterization

Structural characterization of nanosized Fe-doped semiconducting oxide SnO₂ is reported. Samples of Sn_1?x Fe _x O_2?y (with x ranging from 0.11 to 0.33) were processed in a planetary ball mill, subsequently HCl-washed to eliminate metallic iron impurities introduced by the milling tools, and characterized by X-ray diffraction and Mössbauer spectroscopy. Results showed that Fe enters the host matrix randomly replacing Sn in octahedral sites regardless of iron concentration. It has been found the presence of oxygen deficient iron sites attributed to the stoichiometric unbalance of precursor materials used in the milling process. It is known that structural features like particle size and residual microstrain are highly affected by the milling process. Values of average particle sizes as calculated by Scherrer’s method alone decreased with increasing Fe concentration. This result was shown, by means of the Williamson-Hall correction method, to be misleading as a large degree of microstrain is expected for mechanically milled powders. In fact, corrected values of average particle sizes turned out to be reasonably homogeneous regardless of iron content and milling time with no consistent trend. Residual microstrain, on the other hand, was found to increase with iron content giving way to the conclusion that broadening of diffraction peaks are mostly due to increasing microstrain as a function of iron doping and milling time. Williamson-Hall analysis also showed a large degree of particle size inhomogeneity. Milling of undoped SnO₂ showed that this inhomogeneity is due mostly to doping as opposed to milling.     

Preparation and X-ray diffraction, dielectric, and Mössbauer characterization of Co1 − x Ni x Cr2O4 solid solutions

Co_{1 ? x} Ni _x Cr₂O (0 ≤ x ≤ 1) ceramic samples have been characterized by X-ray diffraction and relative dielectric permittivity ?(T), loss tangent tan δ(T) (0.1–200 kHz), and thermally stimulated depolarization current (TSDC) measurements in the range 100–350 K. The samples were shown to consist of spinel solid solutions with a cubic (0 < x ≤ 0.98) or tetragonal (0.99 ≤ x < 1) structure. Increasing the Ni content of the samples from 0 to 100 at % increases their tanδ and 1/ρ by three to four orders of magnitude. The ?(T), tan δ(T), and TSDC of the samples with 0.2 ≤ x ≤ 0.6 have anomalies at T ₁ ～ 220 K and T ₂ ～ 240 K, which point to a transition to a polar state below T ₂. Samples containing 1–4 at % ⁵⁷Fe as an impurity were characterized by Mössbauer spectroscopy in the range 54–330 K and were shown to be magnetically ordered at 78 K. We conclude that the solid solutions have ferroelectric properties with a Curie temperature T ₂ and magnetoelectric multiferroic properties.     

Defect characterization of spray pyrolised β -In<Subscript>2</Subscript>S<Subscript>3</Subscript> thin film using Thermally Stimulated Current measurements

Thermally Stimulated Conductivity (TSC) has been used to analyse defects in the novel material -In₂S₃. These films were deposited using spray pyrolysis technique, varying In:S concentration ratio in the spraying solution. TSC measurements allowed the study of electrical property and non-radiative transitions, due to the defects present in the material. TSC spectra revealed four defects with their prominence varying with In:S concentration ratio. Samples with lower In concentration showed the presence and prominence of indium vacancy. A chemical impurity level due to the presence of chlorine was also detected. Even though sulphur vacancy existed in all the samples irrespective of the variation of In:S concentration ratio its effect decreased with the increase of sulphur concentration. Another defect level was also detected from TSC measurements at high temperature that was attributed to the replacement of sulphur by oxygen which was maximum in films prepared from a spray solution of In:S = 2:3 and minimum for 2:8. This high temperature defect level acts as a neutral center while all the other three levels were seen to be coulomb repulsive. Results from XPS analysis are found to be in good agreement with the TSC results.     

Magnetic phase diagram of solid solutions in the CoCr<Subscript>2</Subscript>S<Subscript>4</Subscript>–Cu<Subscript>0.5</Subscript>In<Subscript>0.5</Subscript>Cr<Subscript>2</Subscript>S<Subscript>4</Subscript> system

The magnetic properties of CoCr₂S₄–Cu_0.5In_0.5Cr₂S₄ solid solutions have been studied in the temperature range 5–300 K at different ac magnetic field frequencies (100, 500, and 1000 Hz) and an amplitude of 79.6 A/m. We have determined the temperatures of the magnetic transformations in the system, identified their nature, and constructed the magnetic phase diagram of the solid solutions.     

Mössbauer spectroscopy and X-ray diffraction of oxide precipitates formed from FeSO4 solution

Chemical and structural properties of oxide precipitates formed from FeSO₄ solution were investigated using X-ray diffraction and⁵⁷Fe Mössbauer spectroscopy. The hydrolysis of urea at elevated temperature was used for the generation of OH^– ions during the precipitation process. The formation of particular oxide phase in the precipitate is strongly dependent on the concentrations of FeSO₄ and urea, as well as on the rate of oxygenation. The phase analysis of precipitates showed the presence of different oxide phases, such as goethite, lepidocrocite, hematite and magnetite, and in one sample of a small amount of siderite. Only substoichiometric magnetite, Fe_3–x O₄, was detected. Significant differences in the Mössbauer spectrum of goethite were observed, due to a very small particle size, the degree of crystallinity and/or different content of structurally bonded water. The correlation between the Mössbauer spectra of precipitated goethite and goethite formed during the atmospheric corrosion of steel is discussed.     

Optical and photoelectric properties of α-Dy<Subscript>2</Subscript>S<Subscript>3</Subscript> and α-Dy<Subscript>2</Subscript>S<Subscript>3</Subscript>〈Pb〉 films

A process is described for the growth of thin crystalline α-Dy₂S₃ films by thermal evaporation from separate dysprosium and sulfur sources. The films were doped with Pb, and their reflection and transmission spectra were measured at room temperature and photon energies in the range (0.3−5.2) × 10⁻¹⁹ J. The α-Dy₂S₃ films were shown to have an exponential absorption edge. The photoconductivity of the doped films was measured at photon energies in the range (0.3−5.2) × 10⁻¹⁹ J and temperatures from 115 to 400 K.     

High- and low-temperature X-ray diffraction studies of aluminate spinels in the CoAl<Subscript>2</Subscript>O<Subscript>4</Subscript>–NiAl<Subscript>2</Subscript>O<Subscript>4</Subscript> system

Co _x Ni_1–x Al₂O₄ (x = 0, 0.25, 0.5, 0.75, 1) aluminate spinels have been prepared by solid-state reactions and their crystal structures have been refined by the Rietveld method. We have analyzed whether the results are consistent with theoretical relationships stemming from the hard sphere model. Using high- and low-temperature X-ray diffraction measurements, we have obtained the temperature dependences of the unit-cell parameters for the synthesized compounds and determined their thermal expansion coefficients. The rate of cation exchange reactions has been shown to be very slow at temperatures below 200°C.     

Local crystal structure of multiferroic BiMnO<Subscript>3</Subscript> studied by <Superscript>57</Superscript>Fe probe Mössbauer spectroscopy

This paper presents a ⁵⁷Fe probe Mössbauer spectroscopy study of a BiMn_0.96⁵⁷Fe_0.04O₃ manganite synthesized at high pressure (6 GPa). The BiMnO₃ manganite possesses multiferroic properties and exhibits cooperative orbital ordering due to Jahn–Teller active Mn³⁺ ions. ⁵⁷Fe Mössbauer spectra have been measured and analyzed in a wide temperature range, which includes the orbital ordering temperature of BiMnO₃.     

Probe Mössbauer Spectroscopy of BiNi<Subscript>0.96</Subscript><Superscript>57</Superscript>Fe<Subscript>0.04</Subscript>O<Subscript>3</Subscript>

This paper presents results of a ⁵⁷Fe probe Mössbauer spectroscopy study of the BiNi_0.96⁵⁷Fe_0.04O₃ nickelate. The spectra measured above its TN demonstrate that Fe³⁺ cations heterovalently substitute for Ni²⁺ nickel (←Fe³⁺), being stabilized on four sites of the nickel sublattice in the structure of BiNiO₃. Calculations in an ionic model with allowance for monopole and dipole contributions to the electric field gradient indicate that the parameters of electric hyperfine interactions between ⁵⁷Fe probe atom nuclei reflect the specifics of the local environment of the nickel in the structure of the unsubstituted BiNiO₃ nickelate. Below T^N, Mössbauer spectra transform into a complex Zeeman structure, which is analyzed in terms of first-order perturbation theory with allowance for electric quadrupole interactions as a small perturbation of the Zeeman levels of the ⁵⁷Fe hyperfine structure, as well as for specific features of the magnetic ordering of the Ni²⁺ cations in the nickelate studied.     

Synthesis and characterization of TiO<Subscript>2</Subscript>–NiO and TiO<Subscript>2</Subscript>–WO<Subscript>3</Subscript> nanocomposites

TiO₂–NiO and TiO₂–WO₃ nanocomposites were prepared by hydrothermal and surface modification methods. The samples were analyzed using X-ray diffraction, Scanning Electron Microscope images, Transmission Electron Microscope, Energy dispersive analysis, Zeta potential, Electrophoretic mobility and Photocatalysis activity measurement. XRD data sets of TiO₂–NiO, TiO₂–WO₃ powder nanocomposite have been studied for the inclusion of NiO, WO₃ on the anatase-rutile mixture phase of TiO₂ by Rietveld refinement. The cell parameters, phase fraction, the average grain size, strain and bond lengths between atoms of individual phases have been reported in the present work. Shifted positional co-ordinates of individual atoms in each phase have also been observed.     

Thermoelectric properties of Sb<Subscript>2</Subscript>Te<Subscript>3</Subscript>–Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> solid solutions prepared through melt solidification in liquids

Using scanning electron and optical microscopies, we have studied the morphology of fracture surfaces and microstructure of samples of an Sb₂Te₃–Bi₂Te₃ solid solution (p-type conductivity) prepared by hot pressing and extrusion of granules produced through melt solidification in liquids. All of the samples were found to contain an additional phase in the form of a tellurium-based eutectic, and their macroscopic structure was shown to depend on the granule comminution procedure. The electrical conductivity, Seebeck coefficient, and thermal conductivity of the samples have been measured in the range 100–700 K. We have obtained materials with the highest dimensionless thermoelectric figure of merit ZT ~ 1.0 at temperatures from 300 to 440 K.     

Mössbauer Analysis and Cation Distribution of Zn Substituted BaFe<Subscript>12</Subscript>O<Subscript>19</Subscript> Hexaferrites

Barium hexaferrite is a well-known hard magnetic material. Doping using nonmagnetic cation such as Zn²⁺ were found to enhance magnetization owing to preferential tetrahedral site (4 f ₁) occupancy of the zinc. However, the distribution of cations in hexaferrites depends on many factors such as the method of preparation, nature of the cation, and chemical composition. Here, Zn-doped barium hexaferrites (Ba_1?xZn_xFe₁₂O₁₉) were synthesized by sol-gel method. In this study, we summarized the magnetic properties of Ba_1?xZn_xFe₁₂O₁₉ (x = 0, 0.1, 0.2, 0.3) BaM, investigated by Mössbauer spectroscopy. Moreover, cation distribution was also calculated for all the products. Mössbauer parameters were determined from 57Fe Mössbauer spectroscopy and according to it, the replacement of Ba-Zn affects all parameters such as isomer shift, the variation in line width, hyperfine magnetic field, and quadrupole splitting. Cation distribution revealed the relative area of undoped BaM, 12k, 2a, and 4 f ₂ positions which are close to theoretical values.     

Crystal structure of a Np(V) sesquioxalate,Na<Subscript>4</Subscript>(NpO<Subscript>2</Subscript>)<Subscript>2</Subscript>(C<Subscript>2</Subscript>O<Subscript>4</Subscript>)<Subscript>3</Subscript>·2H<Subscript>2</Subscript>O

The crystal structure of a previously unknown Np(V) sesquioxalate, Na₄(NpO₂)₂(C₂O₄)₃·2H₂O was studied. The crystal structure consists of neptunyl(V) cations, sodium cations, oxalate anions, and water molecules of crystallization. Neptunyl(V) cations and oxalate ions form anionic chains [(NpO₂)₂(C₂O₄)₃] _n ^4n? . The coordination polyhedron (CP) of Np (pentagonal bipyramid) contains two apical “yl” oxygen atoms and five equatorial O atoms of three oxalate ions. The CP of Na(1) and Na(2) cations are combined through the common edges into zigzag chains in the [010] direction. Two independent oxalate ions are tridentate and tetradentate ligands.     

Temporal Stability of Magnetization of ε-In<Subscript>0.24</Subscript>Fe<Subscript>1.76</Subscript>O<Subscript>3</Subscript> Nanoparticles

The kinetics of spontaneous demagnetization in nanoparticles of the exotic epsilon-phase of indium-doped iron(III) oxide (ε-In_0.24Fe_1.76O₃) has been studied using the method of accelerated testing of magnets for temporal stability in a magnetization-reversal field. Time dependences of the magnetization of nanoparticles measured in a wide range of magnetic fields exhibited rectification in semilogarithmic coordinates. The dependence of the magnetic viscosity on the magnetic field has been measured and used for determining the fluctuation field and activation volume. A relationship between the magnetic viscosity and magnetic noise caused by random thermoinduced magnetization reversal in separate nanoparticles is established.     

Small angles X-ray diffraction and Mössbauer characterization of annealed Tb/Fe multilayer

The effect of thermal annealing on the structure and magnetic properties of crystalline Tb/Fe multilayers has been studied using conversion electron M?ssbauer spectrometry and small-angle X-ray diffraction. The growth of Tb–Fe amorphous alloy from the interface is observed with increasing annealing temperature. After annealing at 873 K, a clear total mixing of the multilayers by interdiffusion has been evidenced. The results are compared with the effect of ion irradiation in the same system.     

Mechanochemically driven amorphization of nanostructurized arsenicals,the case of β-As<Subscript>4</Subscript>S<Subscript>4</Subscript>

The amorphization is studied in mechanically activated β-As₄S₄ using high-energy ball milling in a dry mode with 100–600 min^?1 rotational speeds, employing complementary methods of X-ray powder diffraction (XRPD) related to the first sharp diffraction peak, positron annihilation lifetime (PAL) spectroscopy, and ab initio quantum-chemical simulation within cation-interlinking network cluster approach (CINCA). The amorphous substance appeared under milling in addition to nanostructurized β-As₄S₄ shows character XRPD halos parameterized as extrapolation of the FSDPs, proper to near-stoichiometric amorphous As–S alloys. The structural network of amorphized arsenicals is assumed as built of randomly packed multifold cycle-type entities proper to As₄S₄ network. The depressing and time-enhancing tendency in the PAL spectrum peak is direct indicative of milling-driven amorphization, associated with free-volume evolution of interrelated positron- and Ps-trapping sites. At lower speeds (200–500 min^?1), these changes include Ps-to-positron trapping conversion, but they attain an opposite direction at higher speed (600 min^?1) due to consolidation of β-As₄S₄ crystallites. In respect of CINCA modeling, the effect of high-energy milling is identified as destruction–polymerization action on monomer cage-type As₄S₄ molecules and existing amorphous phase, transforming them to amorphous network of triple-broken As₄S₄ derivatives. These findings testify in a favor of “shell” kinetic model of solid-state amorphization, the amorphous phase continuously generated under speed-increased milling being identified as compositionally authentic to arsenic monosulfide, different in medium range ordering from stoichiometric As₂S₃.     

Structure,dielectric property and impedance spectroscopy of La<Subscript>2/3</Subscript>Cu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> ceramics by sol–gel method

La_2/3Cu₃Ti₄O₁₂ (LCTO) precursor powders were synthesized by the sol–gel method. Effect of sol conditions and sintering process on microstructure and dielectric properties of LCTO powders or ceramics were investigated systematically. The optimum sol conditions for the synthesis of precursor powders were as follows: the Ti⁴⁺ concentration of 1.00 mol/L, the molar ratio of water and titanium of 5.6:1 and the sol pH of 1.0, respectively. After sintered at 1105 °C for 15 h, the LCTO ceramics exhibited more homogeneous microstructure, much higher dielectric constant (ca 09–1.6 × 10⁴) and lower dielectric loss (ca 0.057). The higher dielectric constant of the LCTO ceramics might be due to the internal barrier layer capacitor effect. The LCTO ceramics showed two kinds of conductivity activation energy for grain boundary conductivity from complex impedance analysis. The transition temperature of two activation energy values occured between 170 and 210 °C. The temperature range of 170–210 °C was critical pseudocritical region of the dielectric constant, dielectric loss and activation energy. Furthermore, it was concluded that the grain boundary play an important role for electrical properties.     

Kinetics of the II → III polymorphic transformation in KNO<Subscript>3</Subscript>-RbNO<Subscript>3</Subscript> solid solutions

The formation rate of polymorph III during the II → III phase transition in single crystals of the KNO₃-RbNO₃ solid solutions containing 2.5, 5, and 10 wt % RbNO₃ has been measured as a function of temperature using optical microscopy. The formation rate is shown to increase with increasing ΔT (ΔT = T _tr − T ₀, where T _tr is the transition temperature and T ₀ is the equilibrium temperature). Best fit equations are derived for describing this process, and its activation energy is determined.