Spin states and glassy magnetism in LaCo1−xNixO3 (0 ≤ x ≤ 0.5)

We investigated the effect of Ni substitution on electronic structure and magnetic properties of perovskite LaCoO₃ in the substitution range 0 ≤ x ≤ 0.5. A homovalent +3 state and spin state transition of Co⁺³ has been observed upon Ni substitution in x-ray absorption measurements at the Co and the Ni K-edges. Thermally driven spin state transition has been found to disappear with Ni substitution. A change in nature of magnetic interactions from antiferromagnetic to ferromagnetic and spin glass behavior with substitution is observed in dc and ac magnetization measurements. Ni substitution has been found to lower the average effective magnetic moment which has been ascribed to the decrease in Co/Ni ratio. Changes in fine structure and magnetic properties due to Ni substitution have been explained through the stabilization of intermediate spin state of Co⁺³ by the lattice expansion induced changes in crystal field. The Jahn-Teller distortion is assumed to be suppressed in the expanded lattice and possibility of antiferro-orbital ordering has been proposed for the ferromagnetic super-exchange interactions Co⁺³(IS)–O–Co⁺³(IS). The present work provides possible explanation for the ambiguity in the origin of FM in Co and Ni based perovskite cobaltites as well as supports the idea of lattice expansion induced ferromagnetism.     

Compositional dependence of the optical parameters for Bi5GexSe65−x (30 ≤ x ≤ 45) films

Different compositions of Bi₅Ge_xSe_95−x (x = 30, 35, 40 and 45 at %) thin films were deposited onto cleaned glass substrates by thermal evaporation method. The structural characterization revealed that, the as-prepared films of x = 30, 35 and 40 at. % are in amorphous state but there are few tiny crystalline peaks of relatively low intensity for the film with x = 45 at. %. The chemical composition of the as-prepared Bi₅Ge_xSe_65−x films has been checked using energy dispersive X-ray spectroscopy (EDX). The optical properties for the as-deposited Bi₅Ge_xSe_65−x thin films have been studied. The additions of Ge content were found to affect the optical constants (refractive index, n and the extinction coefficient, k). Tauc’s relation for the allowed indirect transition is successfully describing the mechanism of the optical absorption. It was found that, the optical energy gap (E_g) decreases with the increase in Ge content. These obtained results were discussed in terms of the chemical bond approach proposed by Bicermo and Ovshinsky. The composition dependence of the refractive index was discussed in terms of the single oscillator model.     

Substitutional effect on structural and dielectric properties of Ni1−xAxFe2O4 (A = Mg,Zn) mixed spinel ferrites

The Ni_1−xA_xFe₂O₄ (A = Zn, Mg; x = 0.0, 0.5) ferrites synthesized by chemical co-precipitation method. X-ray diffraction and Raman spectroscopy reveals that all the ferrite samples are in single-phase cubic spinel structure with Fd3m space group. The lattice parameter enhances with Mg and Zn substitution. Raman spectroscopy identifies a doublet like nature of A_1g mode for all the three ferrites. A blue shift in Mg doped ferrite and a red shift in Zn doped ferrite has been observed as compared to parent NiFe₂O₄. Frequency dependent dielectric response confirms the dielectric polarization and electrical conduction mechanism. The minimum value of loss tangent (∼0.03) at 5 KHz suggests that Ni_1−xA_xFe₂O₄ is effective material for microwave application. The activation energy for NiFe₂O₄, Ni_0.5Mg_0.5Fe₂O₄ and Ni_0.5Zn_0.5Fe₂O₄ are found to be 0.28 eV, 0.29 eV and 0.31 eV, respectively.     

Study of dielectric, magnetic and ferroelectric properties in Bi1 − xGdxFeO3

Gd-doped BiFeO₃ polycrystalline ceramics were synthesized by solid-state reaction method and their dielectric and magnetic properties were investigated. X-ray diffraction pattern showed that Bi_1 − xGd_xFeO₃ (x = 0, 0.05 and 0.1) ceramics were rhombohedral. The Gd substitution has suppressed the usual impurity peaks present in the parent compound and we obtained single phase Bi_0.9Gd_0.1FeO₃ ceramic. Gd substitution reduced the antiferromagnetic Néel temperature (T_N) in Bi_1 − xGd_x FeO_3. An anomaly in the dielectric constant(ε) and dielectric loss(tan (δ)) in the vicinity of the antiferromagnetic Néel temperature (T_N) was observed. Ferroelectric and magnetic hysteresis loops measured at room temperature indicated the coexistence of ferroelectricity and magnetism. The room temperature magnetic hysteresis loops were not saturated, but the magnetic moment was found to increase with increase in Gd concentration.     

Tuning the optical properties of alloyed CdSexS1 − x nanoparticles by changing the constituent stoichiometry

The spherical particles CdSe_xS_1 − x with 30-80 nm in radius have been successfully prepared by the hydrothermal reaction at 200 °C. The structure characterization which has been carried out using X-ray diffraction (XRD) shows hexagonal crystal structure. Novel properties have been observed via UV-visual absorption spectra and photoluminescence (PL) spectra. The absorption shoulder and the luminescence emission peaks have been tuned by changing the mole ratio of Se in the CdSe_xS_1 − x samples.     

Static magnetic properties of Co and Ru substituted Ba-Sr ferrite

M-type hexagonal ferrite powders, Ba_0.5Sr_0.5Co_xRu_xFe_(12−2x)O₁₉ (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2) have been synthesized by conventional ceramic method. Magnetic properties have been investigated as a function of substitution of Co and Ru ions at applied external field of 10 kOe. XRD and SEM revealed hexagonal structure for these ferrites. The Co and Ru ions substitution cause increase in saturation magnetization and rapid decrease in magnetocrystalline anisotropy at lower substitution. The magnetic parameters variation has been explained by taking into account preferential site occupancy of sublattice sites by substituted ions. Curie temperature decreases with substitution due to weakening of superexchange interaction. The obtained hysteresis parameters suggest that the proposed materials cannot be used for recording applications.     

Optical properties of CdxZn(1−x)O films deposited by ultrasonic spray pyrolysis method

Cd_xZn_(1−x)O (x = 0, 0.59, 0.78 and 1) films have been produced by ultrasonic spray pyrolysis technique using aqueous solutions of CdCl₂ H₂O and ZnCl₂ on the microscope glass substrate between 325 and 400 °C. The Cd_xZn_(1−x)O samples have been crystallized both cubic and hexagonal structures. The optical properties of the samples were characterized by transmittance and absorption spectroscopy measurements. Transmissions of the samples have decreased with increasing x values. The optical band gap energies of the Cd_xZn_(1−x)O samples from the absorption spectra have been calculated between 2.48 and 3.23 eV by different Zn contents. The samples were annealed at 350 and 450 °C. The optical band gap energy has decreased at 350 °C whereas it increased at 450 °C.     

Thermal expansion properties of Ln2−xCrxMo3O12 (Ln = Er and Y)

Structures and thermal expansion properties of Ln_2−xCr_xMo₃O₁₂ (Ln = Er and Y) have been investigated by X-ray powder diffraction. Rietveld analysis results of Ln_2−xCr_xMo₃O₁₂ indicate that compounds Er_2−xCr_xMo₃O₁₂ (0 ≤ x ≤ 0.3) and Y_2−xCr_xMo₃O₁₂ (0 ≤ x ≤ 0.2) crystallize in orthorhombic structure and exhibit negative thermal expansion, while both monoclinic and orthorhombic compounds Er_2−xCr_xMo₃O₁₂ (1.7 ≤ x ≤ 2.0) and Y_2−xCr_xMo₃O₁₂ (1.8 ≤ x ≤ 2.0) possess positive coefficient of thermal expansion. The coefficients of linear thermal expansion of orthorhombic Ln_2−xCr_xMo₃O₁₂ change from negative to positive with increasing chromium content. Thermogravimetric and differential scanning calorimetry have been used to study the hygroscopicity and the phase transition temperature.     

Crystalline structures and intrinsic magnetic properties of ZnTi-substituted hexagonal M-type Ba ferrite powder

Ion-substituted hexagonal M-type Ba ferrites are studied more and more frequently due to their large magnetic anisotropy and low production cost. In this study, hexagonal M-type Ba ferrite powder specimens with nominal composition Ba(ZnTi)_xFe_12−2xO₁₉ (x = 0.0, 0.2, 0.6, 1.0, 1.4) were prepared via a new route by combining a chemical coprecipitation technique with a conventional ceramic technique. The magnetic properties and crystalline structures were studied by a vibrating sample magnetometer and an X-ray diffractometer, respectively. It was found that small quantities of ZnTi substitutions helped to form single-phase ferrite at a low calcination temperature, which has never been reported before. The magnetic properties were reduced obviously with the increase of x from 0.2 to 1.4, and the best content of substitutions in our case was x = 0.2.     

Sr and Ba substitution in charge ordered Pr0.5Ca0.5MnO3: Sharp steps in the magnetic and transport properties for a narrow composition range

The magnetic and transport properties of Pr_0.5Ca_0.5−xA_xMnO₃ (A = Sr, Ba) have been investigated in this paper. The substitution of Ca with bigger cations such as Sr and Ba can favour the field-induced ferromagnetism and induce sharp steps in the magnetization versus field and resistivity versus field curves. These properties strongly depend on the thermal history of the samples. All the results have been interpreted by a martensitic-like mechanism based on phase separation induced by A-site size mismatch. The above model can also explain the result that the less efficient ability of Sr substitution than Ba substitution to induce ferromagnetism and sharp steps. Another interesting feature in the system is the existence of an optimum substitution range to induce magnetization steps and reach high field-induced magnetization values for both Sr (x = 0.07–0.10) and Ba (x = 0.01–0.08) substitution. We suggest that the disappearance of the steps beyond the optimum substitution range possibly results from the different nature of phase separation in the optimum substitution range and beyond this range.     

Synthesis of layered Li1.2+x[Ni0.25Mn0.75]0.8−xO2 materials (0 ≤ x ≤ 4/55) via a new simple microwave heating method and their electrochemical properties

Li_1.2+x[Ni_0.25Mn_0.75]_0.8−xO₂ (0 ≤ x ≤ 4/55) was prepared by a new simple microwave heating method and the effect of extra Li⁺ content on electrochemistry of Li_1.2Ni_0.2Mn_0.6O₂ (x = 0) was firstly revealed. X-ray diffraction identified that they had layered α-NaFeO₂ structure (space group R-3m). Linear variation of lattice constant as a function of x value supported the formation of solid solution, that is, extra Li⁺ is possibly incorporated in structure of layered Li_1.2Ni_0.2Mn_0.6O₂ (x = 0), accompanying oxidization of Ni²⁺ to Ni³⁺ to form Li_1.2+x[Ni_0.25Mn_0.75]_0.8−xO₂ (0 ≤ x ≤ 4/55). This was confirmed by X-ray photoelectron spectroscopy that Ni³⁺ appeared and increased in content with increasing x value. Charge–discharge tests showed that Li_1.2+x[Ni_0.25Mn_0.75]_0.8−xO₂ (0 ≤ x ≤ 4/55) truly displayed different electrochemical properties (different initial charge–discharge plots, capacities and cycleability). Li_1.2Ni_0.2Mn_0.6O₂ (x = 0) in this work delivered the highest discharge capacity of 219 mAh g⁻¹ between 4.8 and 2.0 V. Increasing Li content (x value in Li_1.2+x[Ni_0.25Mn_0.75]_0.8−xO₂) reduced charge–discharge capacities, but significantly enhancing cycleability.     

Structure and magnetic properties of Ni0.11ZnxCo0.03Fe2.86-xO4 ferrite films deposited on Ag-coated glass substrates by wet chemical method

Ni_0.11Zn_xCo_0.03Fe_2.86-xO₄ spinel ferrite films with x = 0.00, 0.23, 0.34, 0.43 and 0.51 were prepared on Ag-coated glass substrates from nitrate and dimethylamine borane solution at 80 °C. The Ni_0.11Zn_xCo_0.03Fe_2.86-xO₄ ferrite films are singe-phased spinel ferrite. With the Zn content x increasing from 0 to 0.51, the lattice constant of the ferrite films increases from 0.8383 to 0.8425 nm. The Ni_0.11Zn_0.51Co_0.03Fe_2.35O₄ film is about 500 nm thick and composed of uniform equiaxed granules of about 40–50 nm. The Raman spectrum analysis indicates that the Zn²⁺ ions occupy the A sites. Saturation magnetization increases with x increasing from 0 to 0.35, reaches a maximum value of 460 kA/m at x = 0.35, and then decreases with further increase of x. Coercivity decreases monotonically from 12.3 to 1.7 kA/m with x increasing from 0 to 0.51. The change in magnetic properties may be explained by the decrease of A–B interactions and the anisotropy constant due to the incorporation of non-magnetic Zn²⁺ ions.     

Crystal structure and IR spectra of Sr1? x La x Fe1? x Cd x O3?δ

Sr_1−x La _x Fe_1−x Cd _x O_3−δ solid solutions with x = 0.1 and 0.5 prepared at 1270 K are shown to have a cubic perovskite structure and the SrLaFeO₄ structure, respectively. In the range x = 0.25-0.4, the samples consist of a perovskite phase and SrLaFeO₄. As x increases from 0.2 to 0.5, the content of the perovskite phase gradually decreases, and that of the phase isostructural with SrLaFeO₄ increases. The IR spectra of the samples with x = 0.3−0.5 are similar to the spectrum of SrLaFeO₄. The Sr_2/3La_1/3FeO_3−δ ferrite has the perovskite structure, rather than the Sr₂LaFe₃O₈ structure. The synthesis of this ferrite proceeds through the formation of SrFeO_3−δ and LaFeO₃, followed by the mutual dissolution of these orthoferrites. Original Russian Text ? S.V. Smolenchuk, L.A. Bashkirov, M.V. Bushinskii, S.S. Dorofeichik, 2007, published in Neorganischeskie Materialy, 2007, Vol. 43, No. 5, pp. 621–625.     

New Pb-based 1212 Superconductor Containing Phosphorus, (Pb0.75P0.25)Sr2(Y1?xCax)Cu2Oz

New Pb-based 1212 compounds containing phosphorus have been discovered in the (Pb_1−y P _y )Sr₂(Y_1−x Ca _x )Cu₂O _z system; almost the single 1212 phase samples can be obtained for the composition range of 0.0≤x≤0.6 and y=0.25. The crystal structure for each sample has a tetragonal symmetry with the typical lattice parameters a=0.3828 nm and c=1.182 nm. Among them, the sample with x=0.6 and y=0.25 shows the onset of resistivity drop at about 39 K and zero-resistivity at about 17 K. Moreover, the sample shows a diamagnetic signal at about 38 K. These phenomena are found to originate from superconductivity with the bulk feature.     

Yttrium-doped effect on thermoelectric properties of La0.1Sr0.9TiO3 ceramics

Ceramic samples of La_0.1Y _x Sr_0.9–x TiO₃ with different yttrium concentration have been synthesized by conventional solid state reaction technique, and their thermoelectric properties have been investigated. X-ray diffraction characterization confirms that the main crystal structure is of perovskite, but with a small amount of second phase of Y₂Ti₂O₇ for samples with x = 0.05, 0.08, and 0.10. SEM images indicate all ceramic samples are dense and compact, and the largest grain size appears in sample with x = 0.03 and 0.05. Also the second phase can also be identified from the SEM images for x = 0.05, 0.08, and 0.10 samples. Electrical conductivity and Seebeck coefficient of samples have been measured in the temperature range between 300 and 1100 K. With increasing of yttrium concentration, electrical resistivity decreases, and reaches 0.8 mΩ cm for x = 0.10 sample at room temperature. The absolute Seebeck coefficients increase monotonically with increasing temperature in the whole temperature range. Sample with x = 0.03 exhibits the highest absolute Seebeck coefficient 219 μV K⁻¹ at 1059 K, as well as the maximum power factor 11 μW cm⁻¹ K⁻² at 624 K.     

Synthesis and characterizations of Nd doped SrFe12O19 nanoparticles

This is the first report ever on Nd³⁺ doped M-type hexaferrite nanoparticles: SrNd_xFe_12−xO₁₉ (0 ≤ x ≤ 1) prepared by citrate precursor using the sol–gel technique followed by gel to crystallization. The influence of the Nd³⁺ substitution, Fe³⁺/Sr²⁺ molar ratio and the calcination temperature on the crystallization of ferrite phase have been examined using powder X-ray diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), inductance capacitance resistance meter bridge (LCR) and vibrating sample magnetometer (VSM). The structural analysis reveals that the Nd³⁺ ions rearrange themselves in the host lattice without disturbing the parent lattice and Fe³⁺/Sr²⁺ molar ratio less than 12 is more favorable to achieve single phase hexaferrite at calcination temperature 900 °C for 4 h. Mid-IR analysis confirms that Nd³⁺ occupies the octahedral site. Detailed studies of electrical properties of prepared materials have been investigated in the frequency range 100–1000 Hz at room temperature by LCR meter and two probe technique. The result shows that the electrical properties strongly depend upon the frequency of applied field and dopant concentration. The magnetic measurements showing a considerable improvement in coercivity with the substitution of Nd³⁺ on iron sites, while the unsubstituted hexaferrites have highest value of specific saturation magnetization.     

Magnetism in Si1 − xMnx diluted magnetic semiconductor thin films

We have studied the electrical and magnetic properties of p-type semiconductor thin films of Si_1 − xMn_x/Si (x = 0.036 and 0.05) grown by molecular beam epitaxy. Experimental results reveal that the resistivity of the samples decreases gradually with increasing measurement temperature, which can be described well by Mott's variable-range-hopping model. All the samples exhibit the ferromagnetic ordering above room temperature. Among these samples, Si_0.95Mn_0.05 has a higher hole density and magnetization. This indicates an enhancement of hole-mediated ferromagnetic exchange interactions when the Mn-doping concentration is increased.     

Structural, electrochemical and thermal properties of LiNi0.8−xCo0.2CexO2 as cathode materials for lithium ion batteries

A series of cathode materials for lithium ion batteries with the formula LiNi_0.8−xCo_0.2Ce_xO₂ (0 ≤ x ≤ 0.03) were synthesized by sol–gel method using citric acid as a chelating agent. The effects of cerium substitution on the structural, electrochemical and thermal properties of the cathode materials are investigated through X-ray diffraction (XRD), charge–discharge cycling, cyclic voltammogram (CV), electrochemical impedance spectroscopy (EIS) experiments and differential scanning calorimetry (DSC). Results show that the Ce substitution made the layered structure of materials more regular and less cation-ion mixing. An effective improved cycling performance is observed for cerium-doped cathode materials, which is interpreted to a significant suppression of phase transitions and charge-transfer impedance increasing during cycling. The thermal stability of cerium-doped materials is also improved, which can be attributed to its lower oxidation ability and enhanced structural stability at delithiated state.     

Microwave dielectric properties of Ba2 − xSrxLa3Ti3NbO15 ceramics

High dielectric constant and low loss ceramics in the system Ba_2 − xSr_xLa₃Ti₃NbO₁₅ (x = 0-1) have been prepared by conventional solid-state ceramic route. Ba_2 − xSr_xLa₃Ti₃NbO₁₅ solid solutions adopted A₅B₄O₁₅ cation-deficient hexagonal perovskite structure for all compositions. The materials were characterized at microwave frequencies. They show a linear variation of dielectric properties with the value of x. Their dielectric constant varies from 48.34 to 43.03, quality factor Q_u × f from 20,291 to 39,088 GHz and temperature variation of resonant frequency from 8 to 1.39 ppm/°C as the value of x increases. These low loss ceramics might be used for dielectric resonator (DR) applications.     

Microwave dielectric and elastic properties of glass-added Ba6−3xR8+2xTi18O54 (x = 2/3)

Microwave dielectric properties of Ba_6−3xSm_8+2xTi₁₈O₅₄ (x = 2/3) [BST] ceramics with the addition of 0–3 wt.% of various glasses have been studied. It has been found that the addition of 0.5 wt.% of the glasses decreases the sintering temperature by about 150 °C. In general, addition of 0.5 wt.% of Zn, Mg and Pb-based glasses deteriorate the quality factor, whereas aluminum and barium borosilicates do not decrease it considerably. The quality factor and dielectric constant decrease with increasing amount of glass. The temperature coefficient of resonant frequency shifts towards positive or negative depending on the composition of the glass. A glass–ceramic composite with a dielectric constant 64, Q × f nearly 8500 GHz and near to zero τ_f could be obtained at a sintering temperature of 1175 °C when 3–4 wt.% Al₂O₃–B₂O₃–SiO₂ glass was added to BST ceramic. The Young's modulus decreases with increasing amount of glass, irrespective of the composition of glass.