Effect of Sm substitution on the magnetic and electrical properties of Cu-Zn ferrite

Samples of the chemical formula Cu_0.5Zn_0.5Fe_2–x Sm _x O₄ where x = 0.0, 0.02, 0.04, 0.06, 0.08 and 0.1 are studied. X-rays analysis indicated that all investigated samples are formed in a single cubic phase. The lattice parameter is found to increase relative to x = 0.0 except x = 0.02. The grain size is decreased for all samples relative to unsubstituted one except that with x = 0.02. It is noticed that the sample with x = 0.02 has the highest values of initial permeability, magnetization and Curie temperature, T _c. The homogeneity of the samples, the coercive field as well as T _c are found to decrease while the electrical resistivity increases with increasing Sm content.     

Effect of Gd3+ substitution on dielectric properties of nano cobalt ferrite

CoGd_xFe_2 ? xO₄ (x = 0.0, 0.1, 0.3, 0.5) nano magnetic ferrite particles were synthesized by chemical co-precipitation method. The variation of dielectric parameters like dielectric constant, dielectric loss, capacitance and resistance for different Gd³⁺ compositions has been measured at room temperature for frequency dependence in the range of 100 Hz to 10 MHz using impedance analyzer. Results of measurements reveal strong dependence of dielectric parameters on frequency and Gd³⁺ ion content. Dielectric constant, dielectric loss, capacitance and resistance decrease with increasing frequency for all the CoGd_xFe_2 ? xO₄ compositions. Increase in Gd³⁺ ion composition in material, increases the values of dielectric constant, dielectric loss and capacitance while decreases the electrical resistance of nano-particles. A qualitative explanation is given for the composition and frequency dependence of dielectric parameters.     

Grain-oriented fabrication of bismuth titanate ceramics and its electrical properties

The concept of grain-oriented fabrication in ceramics, which utilizes anisotropy either in morphology or some specific property of the particle, is reviewed. A fabrication method, which maximizes the grain orientation, is described for Bi(4)Ti(3)O(12 ). The process utilized plate-like morphology of Bi(4)Ti (3)O(12) particles and yielded a ceramic with an X-ray density of 95.4% and an unprecedented value of 100% for Lotgering's orientation factor in the direction of orientation. The dielectric and piezoelectric properties of this ceramic are described and compared to single crystal values. Complex impedance analysis of the ceramics was used to explain the dielectric relaxations at elevated temperatures. The use of grain-oriented fabrication as a practical technique for making polycrystalline ceramics with electrical properties close to those of single crystals (in the direction of orientation) is emphasized. The use of grain-oriented Bi(4)Ti(3)O(12) ceramics as a high-temperature piezoelectric transducer is suggested.     

Ce-doped bismuth ferrite thin films with improved electrical and functional properties

Bi_1?xCe_xFeO₃ (BCFO) thin film capacitors (x = 0 to 0.2) are fabricated on indium tin oxide coated corning glass substrate by chemical solution deposition method. X-ray diffraction results show a partial phase transition from rhombohedral to tetragonal structure induced in BCFO thin film having preferred (110) orientation with increase in Ce dopant concentration. Current density–field (J–E) characteristics indicate that the leakage current density reduces by several orders of magnitude in Ce-doped BFO thin films resulting from smaller grain sizes and smoother surfaces. Space-charge-limited current and Fowler–Nordheim tunneling are identified as dominating leakage behavior in BCFO thin film capacitors at moderate and high field regions, respectively. Enhanced ferroelectric response with well-saturated (P–E) hysteresis loop is observed for Bi_0.88Ce_0.12FeO₃ thin film having high remnant polarization (P _r—127 µC/cm²) at an applied field of 1080 kV/cm. Bi_0.88Ce_0.12FeO₃ thin film exhibiting well-defined capacitance–field (C–E) butterfly loop with dielectric loss (tan δ—0.03) measured at 10 kHz suggested good ferroelectric properties with high tunability of about 88 %.     

锌铁氧体的合成及磁电性能

用化学共沉淀法制备了系列锌铁氧体微粉。借助于TG-DTA、XRD、SEM、VSM和PNA技术,对干凝胶的热分解过程、产物的物相、微观结构、磁性能和介电常数进行了研究。结果表明,随煅烧温度的提高,锌铁氧体微粉的粒径增大,磁性也增强;尖晶石结构的块状锌铁氧体具有负电阻率温度系数,而且随着煅烧温度的提高,介电常数减小。     

Effect of La3+ substitution on the structural,electrical and electrochemical properties of strontium ferrite by citrate combustion method

The La³⁺ substituted nanocrystalline strontium ferrite has been prepared by citrate combustion method using metal nitrate salts as cation precursors and citric acid as a fuel. The structural characteristics of the compounds have been evaluated using XRD and FTIR. The existence of the single-phase perovskite structure with nanocrystalline size has been confirmed from the X-ray powder diffraction patterns. The stretching and bending vibrations of the metal cations are confirmed from the FTIR spectra. The electrical conductivity of the materials is found to increase with increasing temperature measured by using a modified four-probe technique. The electrochemical behavior has been studied by using potentiostatic polarization method in KOH solutions at two different concentrations of 1 and 2 M. From the polarization studies it has been found that the material La_0.4Sr_0.6FeO₃ gives the lowest corrosion rate of 0.001 mmpy in 1 M KOH solution.     

Effect of Sr substitution on structural,dielectric, magnetic and magnetoelectric properties of rapid liquid sintered BiFe0.8Ti0.2O3 ceramics

Structural, dielectric, magnetic and magnetoelectric properties of polycrystalline Sr doped BiFe_0.8Ti_0.2O₃ ceramics [Bi_1?xSr_x(Fe_0.8Ti_0.2)O₃; x = 0.05, 0.10 and 0.15)] were studied. All the samples were prepared by rapid liquid phase sintering method. Rietveld refinement of X-ray diffraction patterns of all samples confirmed that the samples crystallize in a rhombohedral structure and showed change in Fe–O–Fe bond angle and Fe–O bond length which in turn enhanced magnetization from 0.33 to 0.73 emu/g with the increase in Sr concentration from x = 0.05 to 0.15. The dielectric constant and dielectric loss were observed to increase with the increase in temperature from 30 to 500 °C. An anomalous peak has been observed in dielectric constant versus temperature plot around 300 °C for all the samples, which is close to the magnetic transition temperature of BiFeO₃. The composition-dependent magnetic properties with the expected Fe²⁺/Fe³⁺ ratio fluctuations were correlated by X-ray photoelectron spectroscopy. Magnetic and electric hysteresis loops showed a systematic increase in magnetization and polarization as a result of Sr doping in BiFe_0.8Ti_0.2O₃ ceramics. The value of magnetocapacitance at 10 kHz was observed as 0.95, 1.23 and 1.73 for x = 0.05, 0.10, 0.15 respectively in Bi_1?xSr_xFe_0.80Ti_0.20O₃ ceramics.     

Effect of Pr substitution on structural and electrical properties of BiFeO3 ceramics

Investigation on structural, vibrational, dielectric and ferroelectric properties of Bi_1−xPr_xFeO₃ (x = 0.0, 0.15, 0.25) ceramic samples has been carried out. Room temperature Rietveld-refined X-ray diffraction pattern shows the crystal structure of Bi_1−xPr_xFeO₃ is rhombohedral for x = 0 and triclinic for x = 0.15, 0.25. The changes in Raman normal modes with increasing doping concentration infer the structural transformation is due to Pr substitution at A-site in BiFeO₃. Raman spectra also reveal suppression of ferroelectric behavior due to Pr doping. The dielectric parameters, namely, dielectric permittivity (ε′) and loss tangent (tan (δ)) were evaluated as a function of frequency at room temperature. The ferroelectric polarization reduces in Pr doped bulk BFO samples due to structural change.     

Effect of doping pairs (La,Na) on structural and electrical properties of PZT ceramics

Polycrystalline samples of double-doped PZT with a general formula Pb_0.91(La_1−z/3Na_z)_0.0.9 (Zr_0.65Ti_0.35)_0.9775O₃ [z = 0.0, 0.1, 0.3, 0.5, 0.7] near the morphotropic phase boundary (MPB) have been synthesized by a solution-mixing technique. X-ray structural analysis of the compound shows that there is no change in the crystal structure of PZT on double doping with La and Na. Detailed analysis of the dielectric constant (ɛ) and dissipation factor (tanδ) at different temperatures (room temperature to 350°C) at 10 kHz and frequencies (0.4 to 10 kHz) shows a very dramatic effect of double doping. The transition temperature shifts towards the higher-temperature side with the increase in Na concentration. The dielectric constant is found to increase initially and then to decrease with increasing Na concentration. A diffuse phase transition is observed in these compositions. D.c. resistivity studies have been carried out from room temperature to 300°C and the results are presented.     

Influence of Gd2O3 on phase,microstructure, and electrical properties of ZnO varistor ceramics

Journal of Materials Science: Materials in Electronics - Gd2O3-doped ZnO varistor ceramics were successfully prepared through the solid reaction sintering route. The influence of Gd2O3 additive on...     

Effect of ZnO addition on the sintering and electrical properties of (Mn,W)-doped PZT-PMS-PZN ceramics

The effect of ZnO addition on the phase structure, microstructure and dielectric and piezoelectric properties of 0.2 wt.% MnO₂ and 0.6 wt.% WO₃-doped Pb(Zr_0.52Ti_0.48)O₃-Pb(Mn_1/3Sb_2/3)O₃-Pb(Zn_1/3Nb_2/3)O₃ (PZT-PMS-PZN) ceramics was investigated. X-ray diffraction shows that the phase structure of ceramics is transformed from rhombohedral to tetragonal with the increasing of ZnO addition. The bulk density significantly increases when ZnO is added and then it slightly decreases for ZnO addition above 0.2 wt.%. SEM micrographs show the grains of ceramics are uniform and well developed by adding 0.1 wt.% ZnO. The Curie temperature (T_c) of 270 °C is obtained at the 0.1 wt.% ZnO addition. Mechanical quality factor (Q_m), electromechanical coupling factor (K_p) and piezoelectric constant (d₃₃) increase firstly, and then decrease with the increasing of ZnO addition, while dielectric loss tan δ drops all the time. The Q_m, K_p, d₃₃, tan δ and T_c of the ceramics show the optimum values of 1899, 0.55, 300 (pC/N), 0.0063 and 270 °C, respectively, at the lower sintering temperature of 1120 °C and with 0.1 wt.% ZnO addition.     

Optical and electrical properties of multiferroic bismuth ferrite thin films fabricated by sol-gel technique

Single-phase multiferroic BiFeO₃ thin films have been prepared on LaNiO₃/Si(100) and Si(100) wafer via sol-gel technique. The films are polycrystalline with preferring orientation of (101). The film has a conspicuous absorption in the blue and green light region, and band gap of 2.74 eV. The refractive index and the extinction coefficient of the film is about 2.36 and 0.06 at 600 nm, 2.26 and close to zero in the range of 800-1200 nm, respectively. The films also exhibit favorable ferroelectric and dielectric properties. A large photo induced open-circuit voltage was observed, indicating that the film exhibits photovoltaic behaviours.     

Effect of annealing atmosphere on phase formation and electrical characteristics of bismuth ferrite thin films

Bismuth ferrite thin films were deposited on Pt/Ti/SiO₂/Si substrates by a soft chemical method and spin-coating technique. The effect of annealing atmosphere (air, N₂ and O₂) on the structure and electrical properties of the films are reported. X-ray diffraction analysis reveals that the film annealed in air atmosphere is a single-phase perovskite structure. The films annealed in air showed better crystallinity and the presence of a single BFO phase leading to lower leakage current density and superior ferroelectric hysteresis loops at room temperature. In this way, we reveal that BFO film crystallized in air atmosphere by the soft chemical method can be useful for practical applications, including nonvolatile digital memories, spintronics and data-storage media.     

Influence of Sr and Mn co-doping on the structural,optical, dielectric,multiferroic properties and band gap tuning in bismuth ferrite ceramics

Journal of Materials Science: Materials in Electronics - Solid state reaction was employed to synthesize the Bi1?xSrxFe1?xMnxO3 (x?=?0.05, 0.10, 0.20, 0.25) ceramic...     

Effect of simultaneous substitution of magnesium and niobium on dielectric properties and phase transition temperature of bismuth sodium barium titanate ceramics

(Bi_1/2 Na_1/2)_0.94Ba_0.06Ti_1?x (Mg_1/3Nb_2/3) _x O₃ ceramic samples with x = 0.0, 0.01, 0.05, 0.15, 0.20 were synthesized by solid state method. Microstructure, dielectric properties, impedance and conductivity of the ceramics were studied. Phase formation was confirmed by X-ray diffraction. Co-doping of the ceramics with Mg and Nb at x = 0.01 raised the dielectric constant from 6510 to 8225 at the frequency of 1 KHz. Further increase in (Mg_1/3Nb_2/3)⁴⁺ concentration up to 0.15 increased the transition temperature from 275 °C to 339 °C and lowered the dielectric constant. The ac impedance measurements showed a linear response with frequency at lower temperature indicating insulating behavior and a single semicircular arc with spike at higher temperature.     

Synthesis,structure, and properties of solid solutions based on bismuth ferrite

Solid solutions of Bi_{1 ? x} Pb _x Fe_{1 ? x} Zr _x O₃ (x = 0.1?0.2) are synthesized by the methods of liquid-phase and modified solid-phase synthesis. Also, solid solutions of [Bi_0.9(Pb_0.9Ln_0.1)_0.1][Fe_0.9(Zr_0.65Ti_0.35)_0.1]O₃, and [Bi_0.9(Pb_0.9Ln_0.1)_0.1][Fe_0.9(Zr_0.53Ti_0.47)_0.1]O₃ (Ln - La, Pr, Gd, Yb) are made, including synthesis of their precursors with organic ligands. Comprehensive investigations involving thermal analysis, IR spectroscopy, X-ray powder diffraction, atomic force microscopy, dielectric and magnetic measurements, and neutron powder diffraction are performed. The full-profile analysis of X-ray and neutron diffraction patterns by the Rietveld method shows that, over the whole temperature interval of 10–700 K under study, the Bi_0.9Pb_0.1Fe_0.9Zr_0.1O₃ and Bi_0.8Pb_0.2Fe_0.8Zr_0.2O₃ compounds are characterized by the perovskite structure (space group R3c). The magnetic measurements reveal an antiferromagnetic phase transition in the Bi_0.9Pb_0.1Fe_0.9Zr_0.1O₃ and Bi_0.8Pb_0.2Fe_0.8Zr_0.2O₃ solid solutions. The Néel temperature (T _N ) decreases considerably with growing PbZrO₃ concentration as compared to the Néel point in pure BiFeO₃ (T _N = 633 K). The perovskite structure with a hexagonal distortion is found in lanthanide-substituted solid solutions and specific features of the surface morphology of the ceramics are analyzed. The magnetic measurements suggest the presence of an antiferromagnetic phase transition in the solid solutions under study, with a considerable drop of T _N in the Ln-alloyed compound as compared to the T _N value in pure BiFeO₃     

Effect of bismuth on the properties of Mn ferrite nanoparticles prepared by co-precipitation method

Nanoparticles of MnBi_xFe_2−xO₄(x = 0.0, 0.02, 0.04, 0.06) have been synthesized by a chemical co-precipitation method. X-ray diffraction analysis (XRD) reveals that bismuth exits in its Bi³⁺ and Bi⁵⁺ state. It was also observed that bismuth substitution enhances the grain growth and density. The dielectric constant (ε′) and the loss tangent (tan δ) increases with increase in bismuth content. Resistivity (ρ) and maximum magnetization (M) was found to decrease with increasing bismuth content.     

The effect of Cu substitution on the microstructure and magnetic properties of MnFe2O4 ferrite

The effect of compositional variation on grain size and porosity of Mn_{1 – x} Cu _x Fe₂O₄ ferrite, where x = 0.0, 0.25, 0.50, 0.75, 1.00, prepared by standard ceramic method are reported. From microstructure analysis it follows that porosity increases with the Cu concentration where as coercivity increases up to x = 0.50. Above x = 0.5 the decrease in coercivity is explained on the basis of Neel's mathematical model treating the demagnetizing influence of non-magnetic material in cubic crystals. The coercivity, varies inversely with the grain size upto x = 0.5. The decrease in coercivity above x = 0.5 with grain size can be correlated with the inter-granular domain wall movement because of large porosity.