Structural and dielectric properties of Bi1−xSrxMnO3 (0.40≤x≤0.55)

In order to study the effect of Sr substitution on structural and dielectric properties of Bi_1−xSr_xMnO₃ (0.40≤x≤0.55) compounds were synthesized by the solid state reaction method. The as-prepared samples were characterized by X- ray diffraction (XRD) and dielectric measurements to correlate structural changes with dielectric properties. The XRD data were further analyzed by the Rietveld refinement. The highest dielectric constant was observed in Bi_0.55Sr_0.45MnO₃ and Bi_0.5Sr_0.5MnO₃ systems (∼10⁶) mainly because of orientation polarization. The charge ordering temperature decreases with increasing Sr concentration in Bi_1−xSr_xMnO₃ systems.     

Hopkinson effect,structural and magnetic properties of M-type Sm3+-doped SrFe12O19 nanoparticles produced by a proteic sol–gel process

Samarium doped M-type strontium hexaferrites with chemical formula Sr_1−xSm_xFe₁₂O₁₉ (0≤x≤0.15) (SrM) were synthesized using the proteic sol–gel process. This low cost and environment friendly method yields easily reproducible magnetic powders. The crystal structure and phase purity were studied by X-ray diffraction (XRD). All the XRD patterns have been analyzed by Rietveld refinement technique using the P6₃/mmc space group which showed crystallite size in the nanoscale. Results of field emission scanning electron microscope show that the grains are regular hexagonal platelets. The saturation magnetization reaches a minimum at x=0.10 and increases at higher concentrations. The coercivity increases with Sm³⁺ concentration. The remarkable appearance of a Hopkinson peak at the M vs. T curve indicates that particles of the sample are composed of a single domain particles.     

Finite size effect on Sm3+ doped Mn0.5Zn0.5SmxFe2−xO4 (0≤x≤0.5) ferrite nanoparticles

Samarium doped Mn–Zn ferrite nanoparticles of composition Mn_0.5Zn_0.5Sm_xFe_2−xO₄ (0≤x≤0.5) have been synthesized by a chemical co-precipitation method for developing low Curie temperature stable ferrofluid. These samples were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy Dispersive Spectroscopy (EDS), Electron Paramagnetic Resonance (EPR) spectroscopy and search coil method analytical techniques for their structural, morphological and magnetic properties. X-ray diffraction patterns confirmed the formation of crystalline single spinel phase of as grown nanoparticles. Lattice parameter and lattice strain increases with the increase in Sm³⁺ content. SEM images revealed the presence of ultrafine particles and their agglomerated structures in higher Sm³⁺ ions concentration analogues. The stoichiometry of the final product agreed well with the initial substitution composition as evidenced by EDS data. Electron paramagnetic resonance (EPR) spectra proved the ferromagnetic nature of nanoparticles. The magnetic measurements by search coil method showed superparamagnetism for x=0, 0.1 the samples with saturation magnetization of 23.95 emu/g for Mn_0.5Zn_0.5Fe₂O₄ sample which increases with rise in Sm³⁺ ions content. The results are explained and correlated with the structural, morphological and magnetic properties for developing stable kerosene based ferrofluid by using these nanoparticles.     

Chemical interpretation,enhanced ferroelectric property and dielectric breakdown strength of CuO-added Sr2Nb2O7 ceramics

The structural interpretation and electrical properties of perovskite layer structured (PLS) Sr₂Nb₂O₇-xwt%CuO ceramics prepared by solid-state reaction method are investigated. The chemical interpretation of enhanced piezoelectricity is confirmed to be attributed to the rotation and/or distortion of oxygen octahedron caused by possible Cu²⁺ substitution at the A-site of Sr₂Nb₂O₇ by XRD refinement and variable-temperature Raman spectra. Sr₂Nb₂O₇-xwt%CuO (x?=?0.3, 0.5 and 0.7) ceramics shows enhanced ferroelectric properties with a larger P_r of ～4.1?μC/cm² and a smaller E_c of ～63.1?kV/cm. This study further explains the cations in A-site play a major structural role in the polarization process for PLS system. It was found that dielectric breakdown strength increases up to 258.8?kV/cm and then decreases gradually with the increase of CuO content. Impedance spectroscopy indicated that CuO addition could be helpful in increasing the grain boundary resistance then dielectric breakdown strength.     

Structure,magnetic, electrical transport and magnetoresistance properties of La0.67Sr0.33Mn1−xFexO3 (x=0–0.15) doped manganite coatings

We have undertaken a systematic study of the effect of Fe³⁺ doping on the crystal structure, magnetic, electrical transport and magnetoresistance properties of La_0.67Sr_0.33Mn_1−xFe_xO₃ (0≤x≤0.15) polycrystalline coatings prepared by the sol-gel and screen printing method. The X-ray powder diffraction and Reitveld refinement results indicate that the partial substitution of Mn³⁺ ions by Fe³⁺ ions does not introduce noticeable lattice distortion and structural transition. Magnetic measurements show that Fe³⁺ ions significantly lowers the Curie temperature, and the magnetization at low temperatures first increases and then decreases with further Fe³⁺ doping. The Fe³⁺ doped manganites (x>0.05) are semiconductors with high resistivity, as the consequence of low number of available hopping sites of charge carriers. The most stimulating result obtained is that the magnetoresistance property is greatly enhanced around the percolation threshold (x=0.05) of Fe³⁺ ions in this system and the percolative phase separation is responsible for the anomalous behavior.     

Magnetic and dielectric properties of Zn substituted cobalt oxide nanoparticles

Zinc-substituted cobalt oxide nanoparticles (Zn_xCo_3-xO_4, 0 ≤ x ≤ 0.5) were produced by microwave refluxing technique. The structural, microstructural and magnetic properties of these samples were studied using X-ray diffractometer (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and magnetic property measurement system (MPMS) respectively. XRD and TEM analyses confirmed the single phase nature for all the samples. Rietveld analysis of the samples further confirmed the substitution of Zn-ions into the Co₃O₄ lattice. The chemical states of the elements were studied using X-ray photoelectron spectroscopy (XPS), which suggest the presence of Zn²⁺, Co²⁺, and Co³⁺ ions in the samples. The maximum saturation magnetization (M_S) values of 0.33 Am²/kg was obtained for x = 0.01 sample, and then it continuously reduced with increased Zn content. The dielectric property of the samples was studied in the frequency range of 40 Hz–110 MHz. The samples x = 0.05 and 0.5 displayed the lowest conductivity due to the narrow size distribution of grains.     

The structure,vacancy characteristics,and magnetic properties of GdMn1-xCrxO3 ceramics

To investigate the evolution of the structural and enhanced magnetic properties of GdMnO₃ systems induced by the substitution of Mn with Cr, polycrystalline GdMn_1-xCr_xO₃ samples were synthesized via solid-state reactions. XRD characterization shows that all GdMn_1-xCr_xO₃ compounds with single-phase structures crystallize well and that Cr³⁺ ions entering the lattice sites of GdMnO₃ induce structural distortion. SEM results indicate that the grain size of the synthesized samples (a few microns) decreases as the Cr substitution concentration increases. Positron annihilation lifetime spectroscopy reveals that vacancy-type defects occur in GdMn_1-xCr_xO₃ ceramics and that the vacancy size and concentration clearly change with the Cr content. The temperature and field dependence of the magnetization curves show that Cr substitution significantly influences the magnetic ordering of the gadolinium sublattice, improving the weak ferromagnetic transition temperature and magnetization of GdMn_1-xCr_xO₃. The enhanced magnetization of GdMn_1-xCr_xO₃ is closely related to the vacancy defect concentration.     

Stabilization of α-BiFeO3 structure by Sr2+ and its effect on multiferroic properties

We report a study on the effect of the substitution of Bi³⁺ by Sr²⁺ on the stabilization of R3c structure of Bi_1?xSr_xFeO₃ (0 ≤ x ≤ 0.3, Δx = 0.05), and its effect in the magnetic and dielectric behavior. Stoichiometric mixtures of Bi₂O₃, Fe₂O₃ and SrO were mixed and milled for 5?h using a ball to powder weight ratio of 10:1 by high-energy ball milling. The obtained powder were pressed at 900?MPa to obtain cylindrical pellets and sintered at 800?°C for 2?h. X-ray diffraction and Rietveld refinement were used to evaluate the effect of Sr²⁺ on the crystal structure. In addition, vibrating sample magnetometry (VSM) and dielectric tests were used for describing the multiferroic behavior. The results show that Sr-doped BiFeO₃ particles present rhombohedral structure (R3c) characteristic of α-BiFeO₃ when the doping is below 0.10?mol of Sr. Additionally, a gradual decrease in the amount of secondary phases with the increase of the amount of strontium is observed. For doping concentration higher than 0.15?mol of Sr, a phase transition to an orthorhombic symmetry (β-BiFeO₃, Pbnm) is detected. Besides, changes in relative intensities of reflection peaks planes (110) and (104) are associated with the phase transformations and with the magnetic and dielectric behavior. The α-BiFeO₃ phase show antiferromagnetic behavior and high values of dielectric permittivity, whereas the β-BiFeO₃ phase show a ferromagnetic behavior and low dielectric permittivity.     

Crystal structure,magnetic and electric properties of highly coercive ferrites Sr1 − x Sm x Fe12 − x Zn x O19 (0 ≤ x ≤ 0.4)

The samples of highly coercive ferrites Sr_{1 ? x} Sm _x Fe_{12 ? x} Zn _x O₁₉ (0 ≤ x ≤ 0.4) with the structure of magnetoplumbite have been obtained by the solid-phase method. It has been determined that the samples Sr_{1 ? x} Sm _x Fe_{12 ? x} Zn _x O₁₉ are single-phase at x ≤ 0.2 and contain the impurity phases of α-Fe₂O₃, SmFeO₃, and ZnFe₂O₄ at x ≥ 0.3. In the magnetic fields up to 14 T, the specific magnetization has been measured and the values of coercive force (_σ H _c ) have been determined at 5 and 300 K. It has been shown that semiconductor electroconductivity of single-phase samples Sr_{1 ? x} Sm _x Fe_{12 ? x} Zn _x O₁₉ gradually decreases with the increase in the degree of substitution of x from 0 to 0.2.     

Electronic structure and magnetic properties of Ba1-xSrxCoFe11O19 hexaferrites

We have prepared Ba_1-xSr_xCoFe₁₁O₁₉ hexaferrite nanoparticles (NPs) by using a co-precipitation method. The crystal/electronic structures and magnetic properties were then studied. Results revealed that all Ba_1-xSr_xCoFe₁₁O₁₉ NPs with particle sizes of 100–300?nm crystallized in a hexagonal structure. Both the particle shape and the unit-cell parameters are changed when Sr content (x) increases. The analysis of the electronic structure based on the Fe and Co K-edge XAS spectra proved the oxidation states of Fe and Co to be 3?+?and 2?+?, respectively, which are stable versus an x change in Ba_1-xSr_xCoFe₁₁O₁₉. Local-structural studies also revealed the average bond length between Fe and O of 1.89–1.91?Å less changed by Sr doping. Though the electronic structures of Fe and Co were unchanged, the studies about the magnetic property demonstrated a strong dependence of M_s and H_c on Sr doping. While M_s decreases from 46.1?emu/g for x?=?0–34.2?emu/g for x?=?1, H_c tends to increase from 1630?Oe for x?=?0 to ~ 2200?Oe for x?=?0.5, but slightly decreases to 2040?Oe for x?=?1. We think that the addition of the exchange interaction between Fe³⁺ and Co²⁺ ions and the changes of local-geometric structures and microstructures influenced directly M_s and H_c of NPs.     

Synthesis,structure, optical and magnetic properties of Nd1−xAxMn0.5Co0.5O3−δ (A = Ba,Sr and Ca; x = 0 and 0.25)

The structural, optical, and magnetic properties of polycrystalline Nd_1-xA_xMn_0.5Co_0.5O_3−δ (A = Ba, Sr and Ca; x = 0 and 0.25) perovskite oxides were investigated. The powder XRD pattern demonstrates that the unit cell volume decreases with the changing A-site dopant type. The estimated bandgap energy (Eg) from UV–vis spectroscopic for NdMn_0.5Co_0.5O_3−δ, Nd_0.75Ba_0.25Mn_0.5Co_0.5O_3−δ, Nd_0.75Sr_0.25Mn_0.5Co_0.5O_3−δ and Nd_0.75Ca_0.25Mn_0.5Co_0.5O_3−δ are 3.27, 3.82, 3.79 and 3.53 eV respectively. The substitution of divalent element alters the absorption spectrum, while the redshift optical transition was observed with an increasing ionic radius of dopant. Temperature-dependent magnetization exposes that the Curie temperature (TC) gradually decreases with the decreasing size of alkaline earth metals, and glassy nature was observed at a lower applied magnetic field. The observation of TC can be well explained by the considering of the cationic size disorder parameter in A-site than the random distribution of B-site ions.     

Structural and magnetic properties of Pr–Ni substituted Ca0.5Ba0.5Fe12O19 hexa-ferrite nanoparticles

Effect of Pr–Ni substitution on structural and magnetic properties of Ca_0.5Ba_0.5−xPr_xNi_yFe_12−yO₁₉ (x=0.00–0.10 and y=0.00–1.00) prepared by the sol–gel auto combustion method were investigated. The XRD analysis confirmed the single phase M-type hexa-ferrite structure. The lattice parameters were found to increase as Pr–Ni content increases, which is attributed to the ionic size of the implicated cations. The Pr–Ni seems to be completely soluble in the lattice. Transmission electron microscopy reveals that the grain size decreases with increase of Pr–Ni substitution. The coercivity and remanent magnetization ranges from 1511 to 1925 (Oe) and 21.4 to 26.5 (emu/g), respectively. The coercivity values of all the samples fall in the range of M-type hexa-ferrites.     

A-site strontium doping effects on structure,magnetic, and photovoltaic properties of (Bi1−xSrx)FeO3−δ multiferroic ceramics

Raman spectroscopy, X-ray diffraction (XRD), magnetization hysteresis loop, synchrotron X-ray absorption spectroscopy, and photovoltaic effects have been measured in (Bi_1−xSr_x)FeO_3−δ (BFO100xSr) ceramics for x=0.0, 0.05, 0.10, and 0.15. Raman spectra and XRD reveal a rhombohedral R3c structure in all compounds. A-site Sr²⁺ doping increases fluctuations in cation-site occupancy and causes broadening in Raman modes. BFO15Sr exhibits a strong ferromagnetic feature due to reduction of FeOFe bond angle evidenced by the extended synchrotron X-ray absorption fine structure. The heterostructure of indium tin oxide (ITO) film/(Bi_1−xSr_x)FeO_3−δ ceramic/Au film exhibit clear photovoltaic (PV) responses under blue illumination of λ=405 nm. The maximal power-conversion efficiency and external quantum efficiency in ITO/BFO5Sr/Au are about 0.004% and 0.2%, respectively. A model based on optically excited charges in the depletion region between ITO and (Bi_1−xSr_x)FeO_3−δ can well describe open-circuit voltage and short-circuit current as a function of illumination intensity.     

Dielectric and ferroelectric properties of Ba0.8Sr0.2Ti1−5x/4NbxO3 ceramics

Ba_0.8Sr_0.2Ti_1−5x/4Nb_xO₃ ceramics, x = 0, 0.01, 0.05, 0.10, were fabricated by conventional solid-state reaction. With increasing niobium content the ferroelectric phase transition temperature decreases linearly, and the dispersivity of the transition increases. Niobium B-site decreases transition temperature more pronounced than Sr²⁺ at A-site. The heterovalent substitution of Nb⁵⁺ in low content causes local defect dipole, while more substitutions introduce disorder to disturb the long-range dipole correlation. Ba_0.8Sr_0.2Ti_1−0.5/4Nb_0.1O₃ ceramic shows weak ferroelectric loop at room temperature far from its transition temperature, 153 K.     

Structural,electrical, magnetic and magnetoelectric properties of Fe doped BaTiO3 ceramics

In the present work structural, electrical, magnetic and magnetodielectric properties of BaTi_1−xFe_xO₃ (0%≤x≤10%) ceramics have been investigated. X-ray diffraction (XRD) study reveals that the coexistence of tetragonal and hexagonal phases is strongly influenced by Fe doping concentration. The increase in Fe-doping content leads to the development of hexagonal phase along with an increase in average grain size. A reduction in the dielectric properties is also observed. All BaTi_1−xFe_xO₃ (BTFO) compositions exhibit ferroelectric behavior at room temperature. Remnant polarization (P_r) for pure BaTiO₃ (BTO) has been found to be 7.50 µC/cm² and further decreases with an increase in the Fe concentration. All Fe doped samples exhibit ferromagnetic ordering with saturation magnetization (M_s) being 26 memu/g for x=2.5%. Further, at x=5%, it decreases and thereafter again increases with Fe concentration. The magnetodielectric coefficient increases with Fe doping concentration and highest value found to be 2.80 at x=2.5%.     

Conductivity and electrochemical performance of (Ba0.5Sr0.5)0.8La0.2Fe1−xMnxO3−δ cathode prepared by the citrate-EDTA complexing method

This study reports the successful preparation of single-phase perovskite (Ba_0.5Sr_0.5)_0.8La_0.2Fe_1−xMn_xO_3−δ (x = 0-0.2) by the citrate-EDTA complexing method. The crystal structure, thermal gravity analysis, coefficient of thermal expansion, electrical conductivity, and electrochemical performance of (Ba_0.5Sr_0.5)_0.8La_0.2Fe_1−xMn_xO_3−δ were investigated to determine its suitability as a cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The lattice parameter a of (Ba_0.5Sr_0.5)_0.8La_0.2Fe_1−xMn_xO_3−δ decreases as the amount of Mn doping increases. The coefficients of thermal expansion of the samples are in the range of 21.6-25.9 × 10⁻⁶ K⁻¹ and show an abnormal expansion at around 400 °C associated with the loss of lattice oxygen. The electrical conductivity of the (Ba_0.5Sr_0.5)_0.8La_0.2Fe_1−xMn_xO_3−δ samples decreases as the amount of Mn-doping increases. The electrical conductivity of the samples reaches a maximum value at around 400 °C and then decreases as the temperature increases. The charge transfer resistance, diffusion resistance and total resistance of a (Ba_0.5Sr_0.5)_0.8La_0.2Fe_0.8Mn_0.15O_3-δ-Ce_0.8Sm_0.2O_1.9 composite cathode electrode at 800 °C are 0.11 Ω cm², 0.24 Ω cm² and 0.35 Ω cm², respectively.     

Electrical and magnetic properties of La1−xSrxMnO3 (0.1 ≤ x≤ 0.25) ceramics prepared by sol–gel technique

La_1−xSr_xMnO₃ (0.1 ≤ x ≤ 0.25) high density ceramics were prepared by sol-gel method using methanol as solvent. X-ray diffraction analysis showed that all samples exhibited single perovskite structure and no second phase was detected. Scanning electron microscopy images exhibited good particle connectivity on the surface of sample, and grain size increased with the increase in Sr doping. Resistivity-temperature curves of samples were measured by standard four-probe method, and curves exhibited significant differences in studied range of Sr doping. Magnetic measurement results indicated that the variation of susceptibility of different samples was quite different, and the Curie temperature of samples increased with the increase in Sr content. For x = 0.2, temperature coefficient of resistance value of the sample was larger, and corresponding peak TCR temperature was 307.1 K, which is very close to room temperature. Thus, La_0.8Sr_0.2MnO₃ ceramics exhibited high TCR value close to room temperature. Combined with its excellent magnetic properties, La_0.8Sr_0.2MnO₃ ceramics may potentially act as effective candidates for uncooled radiation calorimeter and uncooled magnetic sensor. Applications of La_0.8Sr_0.2MnO₃ ceramics in uncooled infrared radiation calorimeter at room temperature will be highly beneficial.     

Structural and electrical characterization of Sr- and Al- doped apatite type lanthanum silicates prepared by the pechini method

The subject of this work regards the synthesis of La_9.83−xSr_xSi_6−yAl_yO_26+δ (0≤x,y≤0.5) via a modified Pechini method. The compounds where characterized by XRD and SEM. Pure La_9.83Si₆O_26+δ, La_9.38Sr_0.45Si₆O_26+δ and La_9.38Sr_0.45Si_5.70Al_0.30O_26+δ were prepared after sintering at 1400 °C for 20 h while La_9.38Sr_0.45Si_5.55Al_0.45O_26+δ and La_9.38Sr_0.45Si_5.50Al_0.50O_26+δ contained traces (<8%) of La₂SiO₅ as secondary phase. Rietveld analysis showed that La_9.83−xSr_xSi_6−yAl_yO_26+δ (0≤x,y≤0.5) compounds crystallize in the P6₃/m space group. Al doping on Si site exhibits more pronounced effect upon structural parameters in comparison to Sr doping on La site. Interstitial oxygen accommodates a position at the periphery of the hexagonal channels in the vicinity of the SiO₄ groups. Ion conduction is close related with the size of the hexagonal channels and the interstitial oxygen content. The ion conductivity is promoted when an optimum balance between the aforementioned magnitudes is reached. The LS and LsSa4530 compounds exhibit the highest values of ionic conductivity at 700 °C with 11 and 14 mS/cm and activation energy of 0.47 and 0.46 eV, respectively.     

Structural and mechanical properties of Sr-doped barium niobate thick films

Polycrystalline strontium barium niobates Sr _x Ba_{1 ? x} Nb₂O₆ (SBN, 0.40 ≤ x ≤ 0.75) were prepared by standard solid state ceramic method at relatively at low temperatures. Thick SBN films prepared by simple, low-cost, screen printing route were characterized by XRD. Preliminary structural analysis exhibits the formation of tetragonal tungsten bronze crystal structure at room temperature. Texture coefficient [TC(hkl)], dislocation density (ρ_D), density of crystallites per unit surface area (Ψ), mechanical properties, and microwave behavior of synthesized materials are reported.     

Effect of Sr doped the YFeO3 rare earth ortho-ferrite on structure,magnetic properties,and microwave absorption performance

Given the remarkable performances of rare earth multiferroic ortho-ferrites with magnetic optical and dielectric properties, the Y_1-xSr_xFeO₃ (x = 0, 0.05, 0.1, 0.15) perovskite structure microwave absorbing ferrite materials was successfully synthesized by Sr²⁺ ions A-site doping based on sol-gel technology in this paper. The XRD of all samples was refined with FullProf software, which confirmed the formation of the orthogonal perovskite structure (SG: Pnma). The SEM and TEM results display the average particles size of the samples is distributed between 110 and 160 nm. The increase of Sr doping concentration leads to the increase of particles size, which may be related to the growth of preferred orientation and incomplete substitution. The XPS analysis shows that Fe³⁺ was accompanied by the presence of Fe²⁺ with the doping of Sr²⁺ ions and oxygen vacancies increased significantly. The samples change from weak ferromagnetic state to paramagnetic state with the increase of Sr content. The minimum reflection loss (RL) of the Y_0.95Sr_0.05FeO₃ samples at 12.2 GHz reached −30.87 dB with thickness of 2.2 mm, where its effective absorption bandwidth (EAB, RL ≤ −10 dB) reached 2.4 GHz (11.3–13.7 GHz). Moreover, the EAB of the Y_0.85Sr_0.15FeO₃ samples reached 2.64 GHz, and the corresponding range is 9.0–11.6 GHz (X-band).