Single-phase Character Research Articles

Some Thermomagnetic and Mechanical Properties of Amorphous Fe75Zr4Ti3Cu1B17 Ribbons.

The microstructure, revealed by X-ray diffraction and transmission Mössbauer spectroscopy, magnetization versus temperature, external magnetizing field induction and mechanical hardness of the as-quenched Fe75Zr4Ti3Cu1B17 amorphous alloy with two refractory metals (Zr, Ti) have been measured. The X-ray diffraction is consistent with the Mössbauer spectra and is characteristic of a single-phase amorphous ferromagnet. The Curie point of the alloy is about 455 K, and the peak value of the isothermal magnetic entropy change, derived from the magnetization versus external magnetizing field induction curves, equals 1.7 J·kg−1·K−1. The refrigerant capacity of this alloy exhibits the linear dependence on the maximum magnetizing induction (Bm) and reaches a value of 110 J·kg−1 at Bm = 2 T. The average value of the instrumental hardness (HVIT) is about 14.5 GPa and is superior to other crystalline Fe-based metallic materials measured under the same conditions. HVIT does not change drastically, and the only statistically acceptable changes are visibly proving the single-phase character of the material.

Robust ferromagnetism in rare-earth and transition metal co-doped ZnO nanoparticles for spintronics applications

This work reports on the robust ferromagnetism at room temperature in co-precipitation derived rare-earth (Tb) and transition metal (Co) co-doped ZnO nanoparticles (NPs). X-ray diffraction (XRD) analysis reveals the single-phase character. Morphological studies confirm the formation of spherical-shaped particles with different orientations separated by well-defined grain boundaries. The increase in oxygen vacancies is confirmed by photoluminescence (PL) spectra. The (Tb, Co) co-doped NPs exhibit room temperature ferromagnetic (RTFM) behavior, which has been discussed based on oxygen vacancies mediated magnetic polarons and the effect of grain boundaries.

Investigation of local geometrical structure, electronic state and magnetic properties of PLD grown Ni doped SnO2 thin films

We have investigated the ferromagnetic behavior, electronic states and local geometrical structure of Ni (2 and 10 at %) doped SnO2 thin films. The films were successfully fabricated with the help of pulsed laser deposition (PLD) technique on Si (100) substrate under ultrahigh vacuum (UHV) condition. X-ray diffraction (XRD) results revealed the single phase character of SnO2 rutile lattice structure with P42/mnm space group. The inclusion of Ni ions into SnO2 matrix induced oxygen vacancy (Vo), enhanced the distortion in octahedral local symmetry and reduced the oxidation state of the host Sn4+ (SnO2) to Sn3+ (Sn2O3), these details have been estimated by Raman scattering, Near edge X-ray absorption fine structure (NEXAFS) spectra at Ni L3,2 and O K edges. Further quantitative details on the local geometrical structure around Ni ions were obtained via fitting the experimental Fourier transforms EXAFS spectra |X(R)| with FEFF6 code. The magnetization measurements performed at room temperature (RT) infers that Ni doped SnO2 films displayed ferromagnetic (FM) signal, and there was no significant difference in the saturation moments even with increase in the Ni content. Hence, the similarity in the observed magnetic behavior of the films seems relevant to the same crystal growth condition (UHV) and might not be limited directly to the Ni dopant concentrations. The FM signal and the role of surface defects have been discussed in the light of spin-split impurity band percolation mechanism.

Optical and magneto-optical properties of Nd0.1La0.1Y1.8O3 transparent ceramics

Transparent ceramics in the form of yttrium oxide (Y2O3) doped with La and Nd and pure yttrium as a reference material were successfully prepared via modified EDTA gel process and hot isostatic pressure sintering. Their structure and microstructure were examined by means of scanning electron microscopy and X-ray diffraction, which revealed the high density and single-phase character of these materials. Their optical and magneto-optical properties were also analyzed. Emission spectra of Nd0.1La0.1Y1.8O3 after excitation performed with a continuous 808 nm laser beam showed strong and sharp emission lines. The luminescence lifetime was also investigated. The doped material exhibited a high Verdet constant of over 1000 deg/T m. The figure of merit was calculated in the VIS spectrum. The investigated transparent oxide ceramics can be considered a promising material for application in lasers and magneto-optical devices.

Inhomogeneous Superconducting Behaviour in hbox {La}_{5}hbox {Ni}_{2}hbox {Si}_{3}

The superconducting phase transition at T_mathrm{c} = 2.3 K was observed for the electrical resistivity rho ({T}) and magnetic susceptibility chi (T) measurements in the ternary compound La_{5}hbox {Ni}_{2}hbox {Si}_{3} that crystallizes in the hexagonal-type structure. Although a single-phase character with the nominal stoichiometry of the synthesized sample was confirmed, a small trace of the La–Ni phase was found, being probably responsible for the superconducting behaviour in the investigated compound. The magnetization loop recorded at {T} = 0.5 K resembles a star-like shape which indicates that the density of the critical current can be strongly suppressed by a magnetic field. The low-T _{rho }(T) and specific heat {C}_mathrm{p}({T}) data in the normal state reveal simple metallic behaviour. No clear evidence of a phase transition to any long- or short-range order was found for C_mathrm{p}(T) measurements in the T-range of 0.4–300 K.

Coordination polymer 4,4,10,10-tetramethyl-1,3,7,9-tetraazaspiro[5.5]undecane-2,8-dione with cobalt(II) nitrate: Synthesis and molecular structure

The coordination polymer of cobalt(II) nitrate with bicyclic bis(urea), 4,4,10,10-tetramethyl-1,3,7,9-tetraazaspiro[5.5]undecane-2,8-dione (Sk) {[Co(C11H20N4O2)2(H2O), Co(C11H20N4O2)2(H2O)2]4+(NO3-)4}n (I), is synthesized for the first time, and its atomic structure is determined (CIF file CCDC no. 925792). The crystals of compound I are monoclinic: space group P2/c, a = 26.1284(6), b = 7.1763(2), c = 17.1825(5) A, β = 105.042(3)°, V = 3111.43(15) A3, ρcalcd = 1.474 g/cm3, Z = 2. The powder X-ray pattern at 293 K is refined using the Rietveld method to confirm the single-phase character of the obtained sample of powdered compound I: a = 26.1456(9), b = 7.1810(4), c = 17.1997(11) A, β = 105.016(3)°, V = 3119.0(3) A3. The content of the major phase of compound I in the sample is 100 ± 1%, and impurity phases are absent. The crystal of compound I contains two types of chains oriented along the crystallographic direction [001] with similar structures but differed in the coordination numbers of the cobalt atoms. The Co(1) atom has a coordination number of 5 (trigonal bipyramid), and the coordination number of the Co(2) atom is 6 (octahedron). The nitrate anions are uncoordinated.

PdCu Nanoalloy Electrocatalysts in Oxygen Reduction Reaction: Role of Composition and Phase State in Catalytic Synergy.

The catalytic synergy of nanoalloy catalysts depends on the nanoscale size, composition, phase state, and surface properties. This report describes findings of an investigation of their roles in the enhancement of electrocatalytic activity of PdCu alloy nanoparticle catalysts for oxygen reduction reaction (ORR). Pd(n)Cu(100-n) nanoalloys with controlled composition and subtle differences in size and phase state were synthesized by two different wet chemical methods. Detailed electrochemical characterization was performed to determine the surface properties and the catalytic activities. The atomic-scale structures of these catalysts were also characterized by high-energy synchrotron X-ray diffraction coupled with atomic pair distribution function analysis. The electrocatalytic activity and stability were shown to depend on the size, composition, and phase structure. With Pd(n)Cu(100-n) catalysts from both methods, a maximum ORR activity was revealed at Pd/Cu ratio close to 50:50. Structurally, Pd50Cu50 nanoalloys feature a mixed phase consisting of chemically ordered (body-centered cubic type) and disordered (face-centered cubic type) domains. The phase-segregated structure is shown to change to a single phase upon electrochemical potential cycling in ORR condition. While the surface Cu dissolution occurred in PdCu catalysts from the two different synthesis methods, the PdCu with a single-phase character is found to exhibit a tendency of a much greater dissolution than that with the phase segregation. Analysis of the results, along theoretical modeling based on density functional theory calculation, has provided new insights for the correlation between the electrocatalytic activity and the catalyst structures.

The effect of low temperature thermal annealing on the magnetic properties of Heusler Ni–Mn–Sn melt-spun ribbons

We report the effect of low temperature vacuum annealing (823K; 550°C) on the elemental chemical composition, structural phase transition temperatures, phase structure, and magnetic properties of Ni50.6Mn36.3Sn13.1 as-solidified ribbons. Their elemental chemical composition, highly oriented columnar-like microstructure and single-phase character (L21-type crystal structure for austenite) remain unchanged after this low temperature annealing. Annealed ribbons show a reduction of interatomic distances which lead to a small change in the characteristic phase transition temperatures (~3–6K) but to a significant rise of ~73 and 63% in the saturation magnetization of the martensite and austenite phases, respectively, that can be strictly ascribed to the strengthening of ferromagnetic interactions due to the change in interatomic distances.

Effect of grain size and grain boundary defects on electrical and magnetic properties of Cr doped ZnO nanoparticles

Nanostructure of Zn1−xCrxO (x=0.0, 0.05 and 0.1) were synthesized successfully through sol–gel route. The effects of grain size and grain boundary defects on the electrical and magnetic properties have been investigated. X-ray diffraction (XRD) and selected area electron diffraction (SAED) results reveal the single-phase character. Crystallite sizes were obtained from the XRD patterns whose values are decreasing from ∼27 to ∼16nm with increase in Cr content from 0% to 10% respectively. X-ray photoelectron spectroscopy (XPS) confirms the incorporation of Cr3+/Cr2+ ions in the lattice structure of ZnO, which causes decreasing in the valence electron density of Zn. Dielectric constant (ε) has been explained in the light of Maxwell–Wagner interfacial model, which differentiates between the structure of grain-core and grain-boundary. Complex impedance spectroscopy has been used to separate the grain and grain boundary contributions, the high resistivity values (107 Ω) can be attributed to the dominance of grain boundary resistance. The samples exhibit room temperature ferromagnetic (RT-FM) behavior, which has been discussed based on BMP model and effect of grain/grain boundary structure.

Physical properties of new, lead free (Na0.5Bi0.5)(1−x)BaxTi(1−x)(Fe0.5Nb0.5)xO3 ceramics

This study reports on the synthesis of polycrystalline samples of (Na0.5Bi0.5)(1−x)BaxTi(1−x)(Fe0.5Nb0.5)xO3 with x=0, 0.025, 0.05, 0.075, and 0.1, using the solid-state reaction technique. It investigates the effects of the substitution of sodium and bismuth by barium in the A site and of titanium by iron and niobium in the B site with regard to the free NBT symmetry and dielectric properties were investigated. The crystallographic and dielectric properties were also investigated. The diffractograms showed that all the samples had a single phase character. The increase of ceramic lattice parameters induced an increase in the size of the perovskite lattice. This increase was caused by the increase of the radii of the A and B sites. Room temperature X-ray data revealed that the ceramic structures underwent a gradual distortion with the increase in the composition fraction. Dielectric permittivity was measured in the temperature range of 120–780K with frequencies ranging from 1 to 103KHz. Three anomalies, namely Td, T1 and Tm, were detected and noted to coexist at lower Td and Tm as the rate of substitutions increased. All the samples exhibited a diffuse phase transition and implied better dielectric permittivity maxima values at temperatures approaching room temperature, since the substitution rate values increased more than that of pure NBT. A relaxor behavior with ΔTm=14K and ε'rmax=3876 at 1kHz was observed for (Na0.5Bi0.5)0.9Ba0.1Ti0.9(Fe0.5Nb0.5)0.1O3 ceramic.

Magnetic heating by silica-coated Co–Zn ferrite particles

This study is aimed at the preparation of silica-coated nanoparticles of cobalt–zinc ferrite and their heating properties with respect to potential application in magnetic fluid hyperthermia. The magnetic cores of Co0.4Zn0.6Fe2O4+γ possessing two different sizes were prepared by the coprecipitation method followed by annealing and mechanical treatment. The subsequent encapsulation of the samples by silica led to colloidally stable suspensions in water. The single phase character of the cores was confirmed by x-ray powder diffraction while detailed studies of the coated products by transmission electron microscopy and x-ray photoelectron spectroscopy showed that the silica shell had a thickness of at least 5 nm. The dc magnetic measurements were employed in order to determine the concentrations of magnetic particles in suspensions and to analyse the distribution of blocking temperatures. The heating efficiency of the nanoparticles was studied simultaneously by means of magnetic and calorimetric measurements in various ac fields. Specifically, the magnetic losses were calculated from the ac hysteresis loops while the heating effect of the nanoparticles was determined by measuring the time dependence of the temperature of their suspensions. The evaluation of the heating power from the latter experiments was supplemented by deriving the corrections for non-adiabatic properties of the calorimeter. More accurate results enabled detailed analysis and comparison with data published for other heating agents.

Dielectric and electrical conductivity studies of bulk lead (II) oxide (PbO)

The dielectric properties, the impedance spectroscopy and AC conductivity of bulk PbO have been investigated as a function of frequency and temperature. The measurements were carried out in the frequency range from 40 to 5×106 Hz and in temperature range from 313 to 523K. The frequency response of dielectric constant, ε1, and dielectric loss index, ε2, as a function of temperature were studied. The values of ε1 and ε2 were found to decrease with the increase in frequency. However, they increase with the increase in temperature. The presence of a single arc in the complex modulus spectrum at different temperatures confirms the single-phase character of the PbO. The AC conductivity exhibited a universal dynamic response: σAC=Aωs. The AC conductivity was also found to increase with increasing temperature and frequency. The correlation barrier hopping (CBH) model was found to apply to the AC conductivity data. The calculated values of s were decreased with temperature. This behavior reveals that the conduction mechanism for PbO samples is CBH. The activation energy for AC conductivity decreases with increasing frequency. This confirms that the hopping conduction to the dominant mechanism for PbO samples.

Ferroelectric and magnetic properties of Fe-doped BaTiO3 thin films grown by the pulsed laser deposition

Fe-doped BaTiO3 thin films were grown on (001) oriented SrTiO3 substrates using pulsed-laser deposition technique. These films had a single-phase character and good epitaxial relationship with the substrate. Polarization-electric field (P-E) hysteresis revealed saturated polarization with remnant polarization (Pr) of 13.5 μC/cm2 for 10 mol. % Fe-doped BaTiO3 films. Further increase of composition resulted in the large leakage currents and reduction of polarization. The piezoelectric domain switching in the films was confirmed by local hysteresis using piezoelectric force microscopy measurements. The Fe-doped BaTiO3 thin films exhibited room temperature ferromagnetism, and the magnetization value increased with increasing Fe concentration. Our results demonstrate that the addition of Fe ≤10 mol. % in BaTiO3 induces the ferromagnetism and a switchable ferroelectric state.

Dielectric, modulus and impedance analysis of lead-free ceramics Ba0.8La0.133Ti1−x Sn x O3 (x=0.15 and 0.2)

Titanate barium (BaTiO3)-type oxide ceramics Ba0.8La0.133Ti1−x Sn x O3 (BLTS) (here x=0.15 and 0.2) have been synthesized by the standard solid-state reaction method. Preliminary room temperature X-ray study confirms the formation of single-phase compounds in a rhombohedral crystal system. The electrical properties of BLTS were studied using the ac impedance spectroscopy technique over a wide range of temperature (120–320 K) in the frequency range of 40 Hz to 10 MHz. The presence of a single arc in the complex modulus spectrum at different temperatures confirms the single-phase character of the BLTS compounds.

Properties of Co/Ni codoped ZnO based nanocrystalline DMS

Nanoparticles of Co and Ni codoped zinc oxide, Zn0.9Co0.1−xNixO (x=0.0, 0.03, 0.06 and 0.09), diluted magnetic semiconductors (DMSs) are synthesized by the sol–gel method at annealing temperature of 500°C. X-ray diffraction (XRD) patterns confirm the single phase character of the samples with x=0.0 and 0.03. However, minor NiO secondary phase is detected in the samples with x=0.06 and 0.09. All of them possess the hexagonal wurtzite structure. There is no significant change in the lattice parameters due to variation of doping concentration. The average particle size is found to be 19.31–25.71nm. FTIR and UV–vis spectroscopic results confirm the incorporation of the dopants into the ZnO lattice structure. Magnetization data reveal the presence of room temperature ferromagnetism (RTFM). The XRD patterns rule out the formation of secondary phase of either metallic Co cluster or CoO in the samples. Nevertheless, the secondary phases are a concern in any DMS system as a source of spurious magnetic signals. Therefore, we carried out the XPS studies from which the oxidation states of Co and Ni are found to be Co2+ and Ni2+, respectively. Moreover, XPS O 1s spectra show evidence of the presence of the oxygen vacancy in the ZnO matrix.

Ionic Conduction and Fuel Cell Performance of Ba0.98Ce0.8Tm0.2O3−α Ceramic

The perovskite-type oxide solid solution Ba0.98Ce0.8Tm0.2O3−α was prepared by high temperature solid-state reaction and its single phase character was confirmed by X-ray diffraction. The conduction property of the sample was investigated by alternating current impedance spectroscopy and gas concentration cell methods under different gases atmospheres in the temperature range of 500–900°C. The performance of the hydrogen-air fuel cell using the sample as solid electrolyte was measured. In wet hydrogen, the sample is a pure protonic conductor with the protonic transport number of 1 in the range of 500–600 °C, a mixed conductor of proton and electron with the protonic transport number of 0.945-0.933 above 600 °C. In wet air, the sample is a mixed conductor of proton, oxide ion, and electronic hole. The protonic transport numbers are 0.010–0.021, and the oxide ionic transport numbers are 0.471-0.382. In hydrogen-air fuel cell, the sample is a mixed conductor of proton, oxide ion and electron, the ionic transport numbers are 0.942-0.885. The fuel cell using Ba0.98Ce0.8Tm0.2O3−α as solid electrolyte can work stably. At 900 °C, the maximum power output density is 110.2 mW/cm2, which is higher than that of our previous cell using BaxCe0.8RE0.2O3−α (x≤1, RE=Y, Eu, Ho) as solid electrolyte.

Sonochemical Synthesis of Amorphous Yttrium Iron Oxides Embedded in Acetate Matrix and their Controlled Thermal Crystallization toward Garnet (Y3Fe5O12) and Perovskite (YFeO3) Nanostructures

Sonolysis of stoichiometric mixtures of tris(2,4-pentanedionato)iron, Fe(acac)3, and tris(2,4-pentanedionato)yttrium, Y(acac)3(H2O)3, under Ar atmosphere in tetraglyme led to a colloidal solution from which amorphous Y−Fe−O nanopowders could be precipitated by hexane. These powders are composed of amorphous nanoparticles (3 nm) of yttrium iron(III) oxide embedded in an acetate matrix as proved by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), mass spectrometry, and Mössbauer and IR spectroscopy. The increasing amount (0, 2, 6%) of added water in the reaction mixture was found to lower the organics content in the sonochemical products. The thermally induced crystallization of the amorphous Y−Fe−O nanoparticles was studied by thermal analysis (TG/ DSC), evolved gas analysis (EGA), high-temperature XRD, and Mössbauer spectroscopy. Depending on the Y/Fe starting stoichiometric ratio in the sonicated reaction mixture, the single-phase YFeO3 (YIP) with the perovskite structure or Y3Fe5O12 (YIG) with the garnet structure can be synthesized by such controlled thermal transformation. The single-phase character of crystallized samples and the well-defined structure of both YIP and YIG nanoparticles were confirmed by XRD and Mössbauer spectra excluding the presence of any other phases in the reaction products. The hyperfine parameters of magnetically ordered spectrum of YIP reflect the octahedral environment of high-spin Fe(III) in the perovskite structure, while two nonequivalent octahedral and tetrahedral Fe(III) positions were identified in the YIG garnet spectrum.

Magneto-electric coupling in multiferroic La 0.8Bi 0.2Fe 0.7Mn 0.3O 3 ceramic

We present here the structural, electrical, magnetic and magneto-electric properties of La 0.8Bi 0.2Fe 0.7Mn 0.3O 3 multiferroic sample synthesized by conventional solid state reaction route. X-ray diffraction (XRD) data show single phase character of the sample. Temperature (150–475 K) variation of dielectric constant exhibits step like escalation which consists of two transitions corresponding to the respective peaks in temperature vs. loss tangent curve. Slight shift in peak positions to higher temperatures with the increase of frequency indicates the presence of relaxor behavior. Magnetic field dependent magnetization (M–H) curve at 300 K demonstrates weak ferromagnetic conduct. Coupling between the electric and magnetic orders has been explored by means of magneto-capacitance measurement. Presence of magneto-electric (ME) coupling ascertains the candidature of this material for device application.

Electrical behavior of nano-polycrystalline (La 1− yK y) 0.7Ba 0.3MnO 3 manganites

We present a study of the structural and electrical behavior of nano-polycrystalline mixed barium and alkali substituted lanthanum-based manganite, (La 1− y K y ) 0.7Ba 0.3MnO 3 with y=0.0–0.3. The samples were synthesized by the polymerization complex sol–gel method. The powder X-ray diffraction (XRD) data of the samples show a single-phase character with R 3 ¯ c space group. The magnetic and electrical transport properties of the nano-polycrystalline samples have been investigated in the temperature range 50–300 K and a magnetic field up to 10 kOe. The metal–insulator transition temperature T p of all the samples decreased with potassium doping, and also, it increased slightly with the application of magnetic field. The low field magnetoresistance, which is absent in the single-crystalline perovskite, was observed and increased with decreasing temperature. Comparing the experimental resistivity data with the theoretical models shows that the high temperature electrical behavior of these samples is in accordance with the adiabatic small polaron-hopping model. In the metal-ferromagnetic region the resistivity is found to be quite well described by ρ = ρ 0 + ρ 2 T 2 + ρ 4.5 T 4.5 .

Structural, dielectric, and magnetic properties of La0.8Bi0.2Fe1−xMnxO3 (0.0≤x≤0.4) multiferroics

Polycrystalline multiferroic La0.8Bi0.2Fe1−xMnxO3 (0.0≤x≤0.4) samples were synthesized by the conventional solid state reaction method. Reitveld refinement of the x-ray diffraction patterns confirms the single phase character of all the compositions with orthorhombic structure having space group Pnma (No. 62). Dielectric properties of the samples at temperatures 200–475 K and frequencies 500 kHz–1 MHz authenticate the stabilization of ferroelectric phase with Mn substitution. Dielectric responses of these multiferroics have been analyzed carefully, in the light of “universal dielectric response” model. While cooling from room temperature to 20 K, systematic shifts in magnetization hysteresis loops indicate the presence of exchange bias (EB) phenomenon in the system. Magnetic behavior of these samples has been briefly discussed on the basis of “EB” model for granular systems. Temperature and magnetic field dependent magnetization data demonstrate enhanced magnetization due to the Mn substitution. Magnetocapacitance measurement reveals the magnetoelectric coupling for wide range of temperature (180–280 K) and decrease in dielectric loss at high magnetic field (3 T).