Single or both site doped BiFeO3—Which is better candidate for profound electronic device applications?

Magnesium (Mg) and Zirconium (Zr) doped bismuth ferrite (BiFeO₃; BFO) such as Bi_1?xMg_xFeO₃ (Mg doped BFO; BMO), BiFe_1?xZr_xO₃ (Zr doped BFO; BZO) and Bi_1?xMg_xFe_1?xZr_xO₃ (both Mg and Zr doped BFO; BMZO) were synthesized by solid-state reaction techniques with dopant concentrations x?=?0 and 0.1, respectively. The distorted rhombohedral structures of doped BFO were confirmed by X-ray diffraction analysis. The microstructural analysis revealed that there were uniform dispersions and homogeneous distributions of ceramics in BMZO as compared to BMO, BZO and pure BFO. The presence of both grain and grain boundary in BMZO indicated its good electrical response than others as evidenced from impedance analysis and in agreement with AC conductivity study. The dielectric and ferroelectric measurement signified that BMZO possessed enhanced dielectric constant and high remanent polarization thus could be a better prominent candidate than others to be used in electronic devices.     

Effect of Zn and Mg doping on structural,dielectric and magnetic properties of tetragonal CuFe2O4

The Cu_1?xA_xFe₂O₄ (A = Zn, Mg; x = 0.0, 0.5) ferrites were successfully synthesized by chemical co-precipitation method. X-ray diffraction and Raman spectroscopy reveals that all the ferrite samples are in single-phase with tetragonal structure for CFO and cubic spinel structure for CZFO and CMFO samples. SEM micrograph shows the variation of grain size with Zn and Mg doping in parent CFO sample. Frequency dependent dielectric response confirms the dielectric polarization and electrical conduction mechanism in the present series with a maximum value of dielectric constant and loss tangent for CZFO sample. The anomaly ～493 K in temperature dependent dielectric constant and dielectric loss is assigned to tetragonal to cubic phase transition in CFO sample. The magnetic measurement explored that the saturation value (M_s) is maximum for CZFO as compared to CFO and CMFO ferrites samples.     

Effect of Y2O3 doping on the electrical transport properties of Sr2MnNiFe12O22 Y-type hexaferrite

Y₂O₃ doped Y-type composite hexa-ferrites Sr₂MnNiFe₁₂O₂₂ + xY₂O₃ (x = 0 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%) were synthesized successfully using sol-gel auto combustion technique. X-ray diffraction analysis reveals Y-type hexagonal structure with few traces of secondary phases. The decrease in grain size as a function of Yttrium content is attributed to the fact that Yttrium acts as a grain inhibitor. The DC resistivity was observed to increase with increasing Yttrium-contents due to the unavailability of Fe³⁺ ions at octahedral sites. Activation energy showed that the samples with high resistivity have high value of activation energy and vice versa. Permittivity decreases with the increase of frequency following Maxwell Wagner Model. In addition, the doped samples exhibit very low dielectric constant and low loss tangent in frequency range 20 Hz–1 MHz. The sample x = 5 wt% exhibit the lowest value of dielectric constant. The variation in imaginary part of dielectric constant and loss tangent with frequency show normal dielectric behavior for all the samples. The frequency dependent ac conductivity increases with increase in frequency and decrease with Y₂O₃ doping. These characteristics may be suitable for their potential applications in electromagnetic attenuation materials and microwave devices. The conductivity mechanism so determined was hopping mechanism. The dc resistivity of the doped ferrites measured in our case is about 10¹⁰ Ω-cm that meets the requirement for fabrication of components by electroplating.     

Synthesis and characterizations of Ho2O3 modified SrBi2Nb2O9 ceramics

SrBi_2-xHo_xNb₂O₉ (0?≤?x?≤?0.5) ceramics were prepared through the conventional solid state route. The materials have been characterized by XRD, FTIR and SEM. All compounds were pure and well crystallized. In FTIR spectroscopy, the spectral patterns of the crystal structures of these polyphases are unique and smoothly different from each other. The grains were prone to become spherical with increasing x. Dielectric and electrical properties of these materials as a function of temperature at different frequencies have been carried out. The dielectric constant and dielectric loss were found to decrease with an increase of the holmium concentration at room temperature. Reaching up to x?=?0.4 and x?=?0.5, the diffusivity increases, leading to the occurrence of relaxor behavior. 20–30 at.% Ho doping on the Bi-site can fill up the oxygen vacancies and decrease the AC conductivity. However, at higher doping levels greater than 40% holmium oxide, the AC conductivity is found to increase.     

Reduced conductivity and enhancement of Debye orientational polarization in lanthanum doped cobalt ferrite nanoparticles

In this work we have investigated the conductivity and dielectric properties of CoLa_xFe_2−xO₄ (x=0.0, 0.03, 0.05, and 0.07) nanoparticles synthesized by chemical co-precipitation route. X-ray diffraction analysis confirms the inverse spinal structure of nanoparticles with slight increase in the lattice constant as La concentration increases. Transmission electron microscopy shows spherical nanoparticles with sizes of ∼20 nm. Impedance spectroscopy of the samples was performed in the frequency range 20 Hz-2 MHz at room temperature. The resistance of the grains and grain boundaries was found to increase with lanthanum concentration while the AC conductivity of the samples was observed to decrease with increasing La concentration. Dipolar orientational polarization was found to play an important role in determining dielectric properties of the samples.     

Influence of Al doping on electrical properties of Ni–Cd nano ferrites

We have reported the structural and electrical properties of nano particles of Al doped Ni_0.2Cd_0.3Fe_2.5O₄ ferrite using X-ray diffraction, dielectric spectroscopy and impedance spectroscopy at room temperature. XRD analysis confirms that the system exhibits polycrystalline single phase cubic spinel structure. The average particle size estimated using Scherrer formula for Lorentzian peak (3 1 1), has been found 5(±) nm. The results obtained show that real (ε′), imaginary (ε″) part of the dielectric constant, loss tangent (tan δ), and ac conductivity (σ_ac) shows normal behaviour with frequency. The dielectric properties and ac conductivity in the samples have been explained on the basis of space charge polarization according to Maxwell–Wagner two-layer model and the Koop’s phenomenological theory. The impedance analysis shows that the value of grain boundary impedance increases with Al doping. The complex impedance spectra of nano particles of Al doped Ni–Cd ferrite have been analyzed and explained using the Cole–Cole expression.     

Study on electrical conductivity and phase transition in singly doped BIPBVOX (Bi2V1−xPbxO5.5−x/2) solid electrolyte

Samples of bismuth lead vanadium oxide (BIPBVOX) (Bi₂V_1–xPb_xO_5.5–x/2) singly substituted system in the composition range 0.05 ≤ x ≤ 0.20 were prepared by sol–gel synthesis route. Structural investigations were carried out by using a combination of differential thermal analysis (DTA) and powder X-ray diffraction (PXRD) technique. Energy dispersive X-ray spectroscopy analysis (EDXA) of doped samples was carried out to predict the sample purity and doping concentration. Transitions, α?β, β?γ and γ′?γ were detected by XRD, DTA and variation in the Arrhenius plots of conductivity. The ionic conductivity was measured by AC impedance spectroscopy. The solid solutions with composition x ≤ 0.07 undergo α?β phase transition, at 329 °C and β?γ phase transition at 419 °C. The highly conducting γ′-phase was effectively stabilized at room temperature for compositions with x ≥ 0.17 whose thermal stability increases with Pb content. At 300 °C, the highest value of conductivity 6.234 × 10^?5 S cm^?1 was obtained for composition x = 0.15 and at 600 °C the highest value of conductivity 0.65 S cm^?1 is observed for x = 0.17. AC impedance plots reveal that the conductivity is mainly due to the grain contribution to oxide ion conductivity.     

Effect of nickel doping on structural, optical and electrical properties of TiO2 nanoparticles by sol-gel method

Nickel-doped anatase TiO₂ nanoparticles have been prepared by sol-gel method. The X-ray powder diffraction study reveals that all the prepared samples have pure anatase phase tetragonal system. The average crystallite size of the prepared sample is 14 nm, when found through transmission electron microscope. A strong frequency dependence of both dielectric constant (?′) and dielectric loss (tan δ) were observed for various dopant levels at room temperature in the frequency range of 42 Hz to 5 MHz. At low frequency, the piling up of mobile charge carriers at the grain boundary produces interfacial polarization giving rise to high dielectric constant. The asymmetric shape of frequency dependence of the dielectric loss for the primary relaxation process is observed for each concentration. From the ac conductivity studies, the reduction in conductivity may arise due to the decreasing particle with the increase in Ni-dopant level.     

Dielectric and impedance measurements on (1−x)Ba(Fe1/2Ta1/2)O3-xBa(Zn1/3Ta2/3)O3 ceramics

In this work, ((1−x)Ba(Fe_1/2Ta_1/2)O₃-xBa(Zn_1/3Ta_2/3)O₃), ((1−x)BFT-xBZT) ceramics with x = 0.00–0.12 were synthesized by the solid–state reaction method. X-ray diffraction data revealed that both the powders and ceramics were of a pure-phase cubic perovskite structure. All ceramics showed large dielectric constants. For the x = 0.12 sample, a very high dielectric constant (>20,600) was observed. A lowering in the dielectric loss compared to pure BFT ceramics was observed with the BZT addition. The impedance measurements indicated that BZT has a strong effect on the bulk grain and grain boundary resistance of BFT ceramics. These results are in agreement with the measured dielectric properties. Based on dielectric and impedance results, (1−x)BFT-xBZT ceramics could be of great interest for high performance dielectric materials applications due their giant dielectric constant behavior.     

Growth and characterization of pure and doped organic nonlinear optical single crystal: l-Alanine alaninium nitrate (LAAN)

The pure l-alanine alaninium nitrate (LAAN) single crystals and LAAN crystals doped with lanthanum oxide (La₂O₃), sodium chloride (NaCl), urea (CH₄N₂O), glycine (C₂H₅NO₂) and thiourea (CH₄N₂S) were grown by slow evaporation method. The X-ray diffraction analysis, scanning electron microscopy (SEM), energy dispersive X-ray (EDAX) analysis, UV–vis spectral analysis, dielectric studies and powder SHG measurement are studied systematically. The slight changes in the lattice parameters were observed for the doped crystals compared to pure LAAN crystal. The incorporation of doping into the crystal lattice was confirmed by energy dispersive X-ray analysis. There is no change in the transmission window due to doping and the percentage of transmission in doped samples was found to increase as compared to that of pure LAAN crystal. The dielectric constant of pure crystal was found to be less than that of doped crystals. The AC conductivity was found to increase after doping and with the increase in temperature. A green radiation of 532 nm was observed from the pure and doped LAAN crystals confirming the second harmonic generation (SHG) of the crystals.     

Structural and electrical characterization of BiFeO3–NaTaO3 multiferroic

Using a standard high-temperature solid-state reaction technique, polycrystalline samples of (Bi_1?x , Na _x ) (Fe_1?x , Ta _x ) O₃ (x = 0.0, 0.5) were prepared. The formation of the desired materials was confirmed by X-ray diffraction. The surface texture of the prepared materials recorded by scanning electron microscope exhibits a uniform grain distribution with small voids suggesting the formation of high-density pellet samples. The impedance and dielectric properties of the materials were investigated as a function of temperature and frequency. The relative dielectric constant and loss tangent of BiFeO₃ decrease on addition of NaTaO₃ (x = 0.5). The effect of addition of NaTaO₃ on grain and grain boundary contributions in the resistive and capacitive components of BiFeO₃ was studied using complex impedance spectroscopy. The value of activation energy due to both grain and grain boundary of both the samples is nearly same. The nature of variation of dc conductivity confirms the Arrhenius behavior of the materials. Study of frequency dependence of ac conductivity suggests that the materials obey Jonscher’s universal power law and the presence of ionic conductivity.     

Compare of the electronic structures of F- and Ir-doped SmFeAsO

The electronic structures of Fe-based superconductor SmFeAsO_1−xF_x and SmFe_1−yIr_yAsO are compared through X-ray photoemission spectroscopy in this study. With fluorine or iridium doping, the electronic structure and chemical environment of the SmFeAsO system were changed. The fluorine was doped at an oxygen site which introduced electrons to a reservoir Sm–O layer. The iridium was doped at an Fe site which introduced electrons to a conduction Fe–As layer directly. In a parent material SmFeAsO, the magnetic ordering corresponding to Fe3d in the low-spin state is suppressed by both fluorine and iridium doping through suppressing the magnetism of 3d itinerant electrons. Compared to fluorine doping, iridium doping affected superconductivity more significantly due to an iridium-induced disorder in FeAs layers.     

Synthesis of Fe-doped NiO nanofibers using electrospinning method and their ferromagnetic properties

To make p-type diluted magnetic semiconductor (DMS), Ni_1−xFe_xO nanofibers with different Fe doping concentrations have been successfully synthesized by electrospinning method using polyvinyl alcohol (PVA) and Ni(CH₃COO)₂·4H₂O as starting materials. The nanofibers were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, superconductivity quantum interference device (SQUID) and X-ray photoelectron spectroscopy (XPS) test. The results show that Fe doping has no influence on the diameter and surface morphology of NiO nanofibers, and the nanofibers are polycrystalline with NaCl structure. All Fe-doped samples show obvious ferromagnetic properties and the saturation magnetization is enhanced with increase of the doping concentration of Fe, which indicates that the doped Fe has been incorporated into the NiO host and results in room-temperature ferromagnetism in the Ni_1−xFe_xO nanofibers.     

The role of W doping in response of hydrogen sensors based on MAO titania films

Anatase TiO₂ and W doped TiO₂ films were fabricated by micro-arc oxidation (MAO) on titanium substrates and their hydrogen sensing properties were investigated. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the oxide films and electrochemical impedance spectroscopy (EIS) was applied to investigate the gas sensing mechanism. It is found that the conductivity of TiO₂ films varies with the introduction of W dopant. EIS analysis reveals that the grains and especially the grain boundaries are mainly contributed to the hydrogen response and their equivalent circuits could be represented electrochemically by parallel resistor and constant phase element (CPE). The enhanced sensor signal at higher measuring temperature (300 °C) is observed with an optimal doping concentration of W ions (1.81 at.%).     

Structural,optical and dielectric properties of Ni substituted NdFeO3

Present study reports the structural, optical and dielectric properties of Ni substituted NdFe_1−xNi_xO₃ (0 ≤ x ≤ 0.5) compounds prepared through the ceramic method. X-ray diffraction (XRD) confirmed an orthorhombic crystal structure of all the samples. Both unit cell volume and grain size were found to decrease with an increase in Ni concentration. Morphological study by Scanning electron microscope (SEM) shows less porosity with Ni substitution in present system. From UV–vis spectroscopy, the optical band gap was found to increase with Ni doping. This observed behavior was explained on the basis of reduction in crystallite size, unit cell volume and its impact on the crystal field potential of the system after Ni substitution. The dielectric properties (?′ and tanδ) as a function of frequency or temperature, and the ac electrical conductivity (σ_ac) as a function of frequency have been studied. Hopping of charge carriers between Fe²⁺ → Fe³⁺ ions and Ni²⁺ → Ni³⁺ ions are held responsible for both electrical and dielectric dispersion in the system. Wide optical band gap and a very high dielectric constant of these materials promote them to be a suitable candidate for memory based devices in electronic industry.     

Investigation of phase segregation in Zn1−xMgxO systems

The present work reports on the synthesis of the Zn_1?xMg_xO (x = 0, 0.02, 0.05, 0.10, 0.15 and 0.20) samples by sol–gel method and the investigations on their structural, morphological and optical properties. X-ray diffraction (XRD) data analysis confirms the formation of pure ZnO phase below 10% Mg doping and MgO related phases appears in 10% doped sample indicating that phase segregation of MgO starts at x ≥ 0.10 samples. The phase segregation observed through XRD analysis is also supported by results from Scanning Electron Microscopy (SEM), Raman spectroscopy and photoluminescence studies. Furthermore, the enhancement in optical band gap, with Mg doping, from 3.1 ± 0.1 eV to 3.5 ± 0.1 eV has been observed through UV–Vis spectroscopic analysis. Above results have been discussed on the basis of defects level observed through Raman and photoluminscence studies.     

Grain size effect on the universality of AC conductivity in SnO2

Nanocrystalline tin oxide (SnO₂) material with different grain sizes was synthesized by using a chemical precipitation method. This material was characterized by using the X-ray diffraction and transmission electron microscopy. The electrical properties of compressed nanocrystalline SnO₂ were studied by using impedance spectroscopy. AC conductivity data for SnO₂ material having grain sizes between 9 and 34 nm were analyzed using a power law. The exponent n is found to be 0.5 for bulk (34 nm) and unity for material with grain size below 18 nm. The results show a universal behavior for very low average grain sizes and the non-universal behavior for larger grain sizes even at room temperature.     

Sn1−xBixO2 and Sn1−xTaxO2 (0≤x≤0.75): A first-principles study

The structural, elastic, electronic and optical (x=0) properties of doped Sn_1−xBi_xO₂ and Sn_1−xTa_xO₂ (0≤x≤0.75) are studied using the first-principles pseudopotential plane-wave method within the local density approximation. The independent elastic constants C_ij and other elastic parameters of these compounds have been calculated for the first time. The mechanical stability of the compounds with different doping concentrations has also been studied. The electronic band structure and density of states are calculated and the effect of doping on these properties is also analyzed. It is seen that the band gap of the undoped compound narrowed with dopant concentration, which disappeared for x=0.26 for Bi doping and 0.36 for Ta doping. The materials thus become conductive oxides through the change in the electronic properties of the compound for x≤0.75, which may be useful for potential application. The calculated optical properties, e.g. dielectric function, refractive index, absorption spectrum, loss-function, reflectivity and conductivity of the undoped SnO₂ in two polarization directions are compared with both previous calculations and measurements.     

Effect of Pb on structural and magnetic properties of Ba-hexaferrite

Lead was doped in barium hexaferrite by co-precipitation method and the Pb-doped Ba-hexaferrite with compositions of Ba_1−xPb_xFe₁₂O₁₉ was investigated for the first time at x=0.0, 0.2, 0.4, 0.6, 0.8, 1.0. The molar ratio (Fe³⁺/Ba²⁺) of the solutions was kept 12 while pH was maintained at 13 by using NaOH (M=5) as precipitating agent. Prepared samples were sintered at 965±5 °C for three hours. Structural and morphological studies were done by X-ray diffractometer (XRD) and the scanning electron microscope (SEM). SEM micrographs confirmed the formation of hexagonal plate like structures and particle size was observed to be increased with the increase in Pb concentration. The hysteresis loops obtained from the magnetometer showed that with the increase in Pb concentration, the coercivity decreased while magnetic induction and remanence increased, which in turn increased the maximum energy product (BH)_max. Lower coercivity and the moderate increase in saturation magnetization obtained from Pb doping makes the material useful for magnetic recording media and other frequency based applications.     

Thermal, electrical, and electrochemical properties of Lanthanum-doped Ba0.5Sr0.5 Co0.8Fe0.2O3-δ

Crystal structure, thermogravimetry (TG), thermal expansion coefficient (TEC), electrical conductivity and AC impedance of (Ba_0.5Sr_0.5)_1-xLa_xCo_0.8Fe_0.2O_3-δ (BSLCF; 0.05?x?0.20) were studied in relation to their potential use as intermediate temperature solid oxide fuel cell (IT-SOFC) cathode. A single cubic pervoskite was observed by X-ray diffraction (XRD). The TEC of BSLCF was increasing slightly with the increasing content of La, and all the compounds showed abnormal expansion at high temperature. Proved by the TG result, it was associated with the loss of lattice oxygen. The electrical conductivity, which is the main defect of Ba_0.5Sr_0.5 Co_0.8Fe_0.2O_3-δ (BSCF), was improved by La doping, e.g., the compound of x=0.20 demonstrated a conductivity of σ=376 S cm⁻¹ at 392 °C. The increase of electrical conductivity resulted from the increased concentration of charge carrier induced by La doping. In addition, the AC impedance revealed the better electrochemical performance of BSLCF. For example, at 500 °C, the sample with composition x=0.15 yielded the resistance values of 2.12 Ω cm², which was only 46% of BSCF.