Enhancement in electrical and magnetodielectric properties of Ca‐ and Ba‐doped BiFeO3 polycrystalline ceramics

We carried out a comparative study on the electrical and magnetodielectric properties of polycrystalline BiFeO₃, Bi_0.9Ca_0.1FeO_2.95, Bi_0.9Ba_0.05Ca_0.05FeO_2.95, and Bi_0.9Ba_0.1FeO_2.95 ceramics. The two dielectric anomalies, near 25 K and 281 K, are observed for BiFeO₃. Interestingly, the anomaly near 25 K shifts towards a higher temperature above 60 K with Ca and/or Ba doping, attributed to the doping induced chemical pressure. In addition, the room temperature switchable magnetodielectric effect is witnessed for the doped BiFeO₃ compounds, due to the quadratic magnetoelectric coupling. This indicates the improved magnetoelectric coupling in BiFeO₃ with the Ca and Ba doping. This is essentially due to the enhanced magnetic ordering and reduced leakage current in BiFeO₃ after the doping.     

Enhancement of dielectric,ferromagnetic and electrochemical properties of BiFeO3 nanostructured films through rare earth metal doping

In this present work first assessment of enhanced electrochemical properties of Bismuth Ferrite (BiFeO₃)thin films through Samarium(Sm) doping are delivered. Apart from this enhancement of structural, dielectric and magnetic properties with increasing samarium concentration is discussed. The pure phase BiFeO₃ films and Sm-doped BiFeO3(Bi_1-xSm_xFeO₃ where x = 0.05 & x = 0.1) films were synthesized using 2methoxy aided sol-gel process and were deposited on platinum substrates through spin coating technique. X-ray diffraction confirmed the formation of pure phase BiFeO₃ with Rhombohedral (R3c) structure. Morphological characterization through SEM presented the formation of nanostructures and its structural transformation through doping variant. AFM confirmed the smoothness of the film with a maximum grain size of 172.72 nm for the measured films. The elemental analysis and elemental purity was confirmed through EDAX. Mechanistic aspects of the prepared films were analyzed through Thermogravimetric, Differential Thermal Analysis and Fourier Transform Infrared spectroscopy. The variation of dielectric constant with frequency was measured until 1 MHz and remains almost constant due to the independent nature of polarization with frequency. The magnetic coercivity of the film improved from 77.7G to 240G with samarium doping. The Bi_0.9Sm_0.1FeO₃ films deposited on platinum substrates enhanced the specific capacity to about 184Fg^-1 along with its retention capability enabling it to be used as electrode material for supercapacitors.     

Structural,dielectric, vibrational and magnetic properties of Sm doped BiFeO3 multiferroic ceramics prepared by a rapid liquid phase sintering method

Rare earth Sm substituted Bi_1−xSm_xFeO₃ with x=0, 0.025, 0.05, 0.075 and 0.10 polycrystalline ceramics were synthesized by a rapid liquid phase sintering method. The effect of varying composition of Sm substitution on the structural, dielectric, vibrational, optical and magnetic properties of doped BiFeO₃ (BFO) ceramics have been investigated. X-ray diffraction patterns of the synthesized rare earth substituted multiferroic ceramics showed the pure phase formation with distorted rhombohedral structure with space group R3c. Good agreement between the observed and calculated diffraction patterns of Sm doped BFO ceramics in Rietveld refinement analysis of the X-ray diffraction patterns and Raman spectroscopy also confirmed the distorted rhombohedral perovskite structure with R3c symmetry. Dielectric measurements showed improved dielectric properties and magnetoelectric coupling around Néel temperature in all the doped samples. FTIR analysis establishes O–Fe–O and Fe–O stretching vibrations in BiFeO₃ and Sm-doped BiFeO₃. Photoluminescence (PL) spectra showed visible range emissions in modified BiFeO₃ ceramics. The magnetic hysteresis measurements at room temperature and 5 K showed the increase in the magnetization with the increase in doping concentration of Sm which is due to the structural distortion and partial destruction of spin cycloid caused by Sm doping in BFO ceramics.     

Structural,magnetic and photocatalytic properties of Sr2+ doped BiFeO3 nanofibres fabricated by electrospinning

Sr²⁺ doped BiFeO₃ (Bi_1-xSr_xFeO₃, 0?≤x?≤?0.35) nanofibres were fabricated by a sol-gel based electrospinning method. The as-spun BiFeO₃ (BFO) nanofibres consist of fine grained particles with high crystallinity. With Sr²⁺ doping, both the magnetic and photocatalytic properties of BFO are effectively improved. The best photocatalytic property for degradation of the methylene blue (MB) is obtained in Bi_0.75Sr_0.25FeO₃ nanofibres due to their weakest photoluminescence (PL) intensity. Meanwhile, the photocatalytic property of Bi_0.75Sr_0.25FeO₃ nanofibres is much higher than that of nanoparticles with the same constituent, which is attributed to the unique one-dimension fibrous structure benefiting the separation and decreased recombination of e^-/h⁺ pairs. This work proposes an effective approach for the degradation of organic pollutes.     

Structural transformation and multiferroic properties of Sm and Ti co-doped BiFeO3 ceramics with Fe vacancies

Sm and Ti co-doped BiFeO₃ (BFO) ceramics with Fe vacancies—Bi_0.86Sm_0.14FeO₃, Bi_0.86Sm_0.14Fe_0.99Ti_0.01O₃, and Bi_0.86Sm_0.14Fe_0.9Ti_0.05O₃—were prepared by a solid-state method using a rapid liquid process. X-ray diffraction indicated that all samples exhibited a rhombohedral structure with a minor secondary phase. The structural transformation from a rhombohedral (space group: R3c) to orthorhombic structure (space group: Pnma) was observed in the sample of Bi_0.86Sm_0.14Fe_0.9Ti_0.05O₃, which was also confirmed by Raman scattering spectra. Microstructural investigations with scanning electron microscopy showed a reduction in grain size with doping of BFO. The dielectric loss of Bi_0.86Sm_0.14Fe_0.9Ti_0.05O₃ reaches 0.05 (at 100 Hz) owing to the introduction of Ti and Fe vacancies. Ferroelectromagnetic measurements revealed the existence of ferroelectricity with a remanent polarization of 0.24 µC/cm² in Bi_0.86Sm_0.14FeO₃, paraelectricity in Bi_0.86Sm_0.14Fe_0.9Ti_0.05O₃, and weak ferromagnetism with a remanent magnetization of 0.2 emu/g in Bi_0.86Sm_0.14Fe_0.99Ti_0.01O₃. The two composition-driven phases exist simultaneously and the different coercive field might be related to the jumps in the ferromagnetic hysteresis loops. Both the ferroelectric and magnetic properties were shown to correlate with the composition-driven structural evolution.     

Effects of Ho and Ti Doping on Structural and Electrical Properties of BiFeO3 Thin Films

Effects of Ho and Ti ions individual doping and co‐doping on the structural, electrical, and ferroelectric properties of the BiFeO₃ thin films are reported. Pure BiFeO₃, (Bi_0.9Ho_0.1)FeO₃, Bi(Fe_0.98Ti_0.02)O_3+δ, and (Bi_0.9Ho_0.1)(Fe_0.98Ti_0.02)O_3+δ thin films were prepared on Pt(111)/Ti/SiO₂/Si(100) substrates by using a chemical solution deposition method. All thin films were crystallized in distorted rhombohedral structure containing no secondary or impurity phases confirmed by using an X‐ray diffraction study. Changes in microstructural features, such as grain morphology and grain size distribution, for the doped samples were analyzed by a scanning electron microscopy. From the experimental results, a low electrical leakage (1.2 × 10^?5 A/cm² at 100 kV) and improved ferroelectric properties, such as a large remnant polarization (2P_r) of 52 μC/cm² and a low coercive field (2E_c) of 886 kV/cm, were observed for the (Bi_0.9Ho_0.1)(Fe_0.98Ti_0.02)O_3+δ thin film. Fast current relaxation and stabilization observed in the (Bi_0.9Ho_0.1)(Fe_0.98Ti_0.02)O_3+δ imply effective reduction and neutralization of charged free carriers.     

Red-emitting enhancement of Bi4Si3O12:Sm3+ phosphor by Pr3+ co-doping for White LEDs application

In this account, Bi₄Si₃O₁₂:Sm³⁺ and (Bi₄Si₃O₁₂:Sm³⁺, Pr³⁺) red phosphors were prepared by solution combustion method fueled by citric acid at 900 °C for 1 h. The effects of co-doping Pr³⁺ ions on red emission properties of Bi₄Si₃O₁₂:Sm³⁺ phosphors, as well as the mechanism of interaction between Sm³⁺ and Pr³⁺ ions were investigated by various methods. X-ray diffraction (XRD) and Scanning electron microscopy (SEM) revealed that smaller amounts of doped rare earth ions did not change the crystal structure and particle morphology of the phosphors. The photoluminescence spectroscopy (PL) indicated that shape and position of the emission peaks of (Bi₄Si₃O₁₂:Sm³⁺, Pr³⁺) phosphors excited at λ_ex=403 nm were similar to those of Bi₄Si₃O₁₂:Sm³⁺ phosphors. The strongest emission peak was recorded at 607 nm, which was attributed to the ⁴G_5/2→⁶H_7/2 transition of the Sm³⁺ ion. The photoluminescence intensities of Bi₄Si₃O₁₂:Sm³⁺ phosphors were significantly improved by co-doping with Pr³⁺ ions and were maximized at Sm³⁺ and Pr³⁺ ions doping concentrations of 4 mol% and 0.1 mol%, respectively. The characteristic peaks of Sm³⁺ ions were displayed in the emission spectra of (Bi₄Si₃O₁₂:Sm³⁺, Pr³⁺) phosphors excited at respectively λ_ex=443 nm and λ_ex=481 nm (Pr:³H₄→³P₂, ³H₄→³P₀). This indicated the existence of Pr³⁺→Sm³⁺ energy transfer in (Bi₄Si₃O₁₂:Sm³⁺, Pr³⁺) phosphors.     

Sites occupancy preference of Bi3+ and white light emission through co‐doped Sm3+ in LiGd5P2O8

Bi³⁺, Sm³⁺‐activated LiGd₅P₂O₈ (LGPO) phosphors were prepared through high‐temperature solid‐state method. In LGPO host, there are 5 types of Gd crystallographic sites, named as Gd(1)/Gd(2)/Gd(3)/Gd(4), and Gd(5). Bi³⁺‐activated LGPO phosphors exhibit 1 broad excitation band from 250 to 320 nm centered at 293 nm and a broad asymmetric emission band ranging from 350 to 600 nm with the maximum value approximately at 409 nm. It can be concluded from dual‐emission spectra that Bi³⁺ may occupy 2 Gd sites and an obvious spectral blue‐shift appeared with increasing Bi³⁺ content, which is caused by the intensity of crystal field of Bi³⁺ is decreased. Notably, through the calculation of each Gd‐O chemical parameter, the environmental factor (h_e) value of each Gd site can be obtained and it can be further inferred that 2 emission bands centered at 409/461 nm are ascribed to Bi³⁺ ions which occupies Gd(3) and Gd(4) sites, respectively. Energy transfer from Bi³⁺ to Sm³⁺ ions in Bi³⁺/Sm³⁺ co‐doped LGPO samples occurred and it realizes the color‐tunable emission from cyan to yellow including white‐light emission, through controlling Sm³⁺ content. Moreover, energy transfer mechanism between Bi³⁺ and Sm³⁺ ions is verified to be dipole‐dipole interaction by analyzing the spectroscopic experimental results and the critical distance between them is calculated to be 8.22 Å by concentration quenching method. Finally, it is illustrated that Bi³⁺ and Sm³⁺ co‐doped LGPO phosphors will be a promising candidate for n‐UV chip pumped w‐LEDs.     

Enhanced magnetic and dielectric properties of Y doped bismuth ferrite nanofiber

Yttrium doped Bismuth ferrite (BFO) nanofiber was fabricated via a sol-gel-based electrospinning process with the fiber diameter in the range of 60–220 nm. The crystal structure, magnetic and dielectric properties were investigated at room temperature. The Rietveld refinement results indicate the phase transition from space group R3c to Pbnm by the Y doping. Dramatic increase of magnetization has been achieved in Y doped BFO nanofiber. Compared with BFO nanoparticle, the Bi_0.95Y_0.05FeO₃ nanofiber exhibits nearly eighteen-fold improved magnetization, which is the strongest in the reported Y doped BFO at the same doping level. The largely improved magnetization mainly originates from the serious suppression of spiral spin structure by the small crystal size of nanofiber structure. Moreover, the Bi_0.95Y_0.05FeO₃ nanofiber holds the lower dielectric loss and obvious dependence of the capacitance on bias voltage, indicating the improved ferroelectricity due to the decreased leakage current. The simultaneous enhancement of ferroelectricity and magnetization in Y doped BFO nanofiber suggests that nanofiber structure plays an important role in improving multiferroic performance.     

Tailoring the multiferroic properties of BiFeO3 by co-doping Er at Bi site with aliovalent Nb,Mn and Mo at Fe site

Single phase multiferroic undoped BiFeO₃ notoriously suffers due to the poor spin–charge coupling resulting in limitations to device applications. The present work focuses on the tailoring of its multiferroic and magnetoelectric coupling properties by synthesizing multiferroic Bi_0.95Er_0.05Fe_0.98TM_0.02O₃ (TM = Nb, Mn and Mo) ceramics. The ferroelectric, magnetic, current leakage measurements and magnetoelectric effect were investigated. XRD along with the Reitveld refinement results confirms that all the samples possess perovskite based rhombohedral structure and reveals that doping of (Er, Nb), (Er, Mn) and (Er, Mo) induced the crystallographic distortion in the BFO lattice and hence induced a variation in the bond lengths and bond angle. Dual doping significantly enhanced the electrical, magnetic properties and magnetoelectric coupling as compared to BiFeO₃. Doping has lowered the leakage current by three to four orders compared to BFO. The lattice distortion, reduced leakage current and destruction of spin–cycloidal structure could be the origin for these improved features. The (Er, Nb) doped BiFeO₃ yields enhanced ferroelectric character with the maximum polarization value of 0.46 µC/cm², maximum ME coupling of 0.22 mV/cm at a magnetic field of 130 G, an improved magnetization with a remanance value of 0.0903 emu/g and the lowest leakage current density.     

Crystal structure,leakage conduction mechanism evolution and enhanced multiferroic properties in Y-doped BiFeO3 ceramics

Ceramics of pure phase Yttrium (Y) doped BiFeO₃ prepared by a solid-state sintering route were characterized by X-ray diffraction, Raman spectroscopy, magnetic and electrical measurements. The results and analysis show that Y substitution greatly reduces the leakage current and enhances the multiferroic properties of BiFeO₃. Leakage conduction mechanism is shown to change from space-charge-limited conduction type in pure BiFeO₃ to a Poole–Frenkel emission behavior in Bi_0.90Y_0.10FeO₃. A Fowler-Nordheim tunneling mechanism in Bi_0.95Y_0.05FeO₃ ceramic is also evidenced under high electric fields. At the same time, enhanced magnetic properties due to Y-doping are confirmed by temperature dependent magnetometry and supported by Raman spectroscopy. An unexpected and sharp switching behavior in the magnetization under low magnetic fields observed in Bi_0.90Y_0.10FeO₃ ceramic, together with its improved ferroelectric property, may trigger such system for promising magneto-electric applications.     

Effect of Sm doping on structure,dielectric and magnetic properties of GdFeO3

Nano-particles of GdFeO₃ (GFO) and Gd_0.4Sm_0.6FeO₃ (GSFO) were synthesized by sol-gel auto-combustion method to study the effect of Sm³⁺doping on physical properties of GFO. Rietveld refinement of x-ray diffraction pattern confirms the proper phase formation of samples and the average octahedral <Fe–O1–Fe> angle of GSFO is found to be 145.54⁰ which is larger compared to GFO 142.53⁰. Temperature dependent DC magnetization measurements showed that Sm doping in GdFeO₃introduces spin-reorientation transition which is absent in pure GdFeO₃ phase. The dielectric constant of GSFO is found to be larger than that of GFO because of change in hybridization between the O-2p states and Fe-3d states. In both the ceramics at higher temperatures (above 150 °C) conduction mechanism is taking place via oxygen defect charge carrier hoping. The complex impedance analysis revealed that the distribution of relaxation time of charge carriers is temperature independent. Sm doping in GFO not only changed the dielectric properties but also changed the magnetic coercive field and shape of the magnetic isotherm of GFO.     

Achieving high-energy storage performance in 0.67Bi1-xSmxFeO3-0.33BaTiO3 lead-free relaxor ferroelectric ceramics

BiFeO₃–BaTiO₃ (BF-BT)-based lead-free ferroelectric ceramic has attracted immense interest in energy storage applications due to its great spontaneous polarization (P_max) strength. However, high remanent polarization (P_r) has become a serious obstruction for its practical application. In this work, Sm ions were doped into 0.67BiFeO₃-0.33BaTiO₃ (0.67Bi_1-xSm_xFeO₃-0.33BaTiO₃, BS_xF-BT) to tailor the structure and energy storage properties. It was found that the doping of Sm ions effectively reduced P_r by enhancing the relaxor behavior of BF-BT ceramic, which produce an enhancement in the energy storage performance. Large recoverable energy storage density W_rec of 2.8 J/cm³ with moderate energy storage efficiency η of 55.8% (200 kV/cm) were achieved in the ceramics with x = 0.1. Moreover, the energy storage capabilities exhibited good stability at temperature (20–95 °C) and frequency (0.1–50 Hz). Furthermore, the ceramic also possessed a predominant discharge speed with a discharge time less than 0.1 μs in a circuit with a load of 200 Ω. These results showed that the W_rec and η of BF-BT ceramic could be availably promoted by the doping of Sm ions, which may be helpful for the enhancement of energy storage performance of BF-BT-based ceramics.     

Luminescence properties and thermometric performance of Bi3+/Sm3+-codoped BaLa2ZnO5 phosphors

A zincate material, BaLa₂ZnO₅ was successfully synthesized by a high-temperature solid-state method as a host for Bi³⁺. All the peaks in the X-ray diffraction patterns of the obtained material could be attributed to single phase BaLa₂ZnO₅. The BaLa₂ZnO₅ host exhibited strong band-to-band absorption in the range of 200–290 nm. After the doping of Bi³⁺, the absorption band due to band-to-band transition decreased, and three new absorption bands appeared. Upon monitoring the luminescence of Bi³⁺ at 407 nm, three excitation peaks were observed for BaLa₂ZnO₅: Bi³⁺, which could be attributed to A, C and metal-to-metal charge-transfer states by analyzing its excitation and absorption spectra. When codoped with Bi³⁺ and Sm³⁺, BaLa₂ZnO₅: Bi³⁺/Sm³⁺ exhibited strong energy transfer process from Bi³⁺ to Sm³⁺. Variable-temperature emission spectra revealed that the luminescence intensity of Bi³⁺ decreases rapidly with the increase in temperature, while that of Sm³⁺ ions decreases slowly. The relative sensitivity (S_R) values of the BaLa₂ZnO₅: Bi³⁺ and BaLa₂ZnO₅: Bi³⁺/Sm³⁺ phosphors to temperature (1.77 and 1.12% K⁻¹, respectively) were high and extremely stable in the range of 293–423 K. Therefore, the Bi³⁺-doped BaLa₂ZnO₅ phosphor has great application potential for biological temperature sensing.     

White luminescence of bismuth and samarium codoped Y2O3 phosphors

In this work Sm³⁺ (0–2.0 at%) and Bi³⁺ (0–2.0 at%) doped Y₂O₃ luminescent powders were prepared by a sol–gel method from yttrium acetylacetonate, samarium and bismuth nitrates as metal sources. The as prepared powders (chemical composition is close to stoichiometric Y₂O₃) present the cubic structure from 700 °C, and at 900 °C are characterized by the presence of rounded particles with heterogeneous size of 42.9 nm. Luminescent effect of ions of Sm³⁺ and Bi³⁺ into Y₂O₃ host as was studied on heat treated powders from 800 to 1100 °C. The combination of the red luminescence from the Sm³⁺ ions and the bluish from Bi³⁺, makes the synthesized phosphors candidates to be used in fabrication of phosphor-converted light-emitting diodes (LEDs).     

Structural,Raman, and Dielectric Studies on Multiferroic Mn‐doped Bi1−xLaxFeO3 Ceramics

Multiferroic Bi_1?xLa_xFeO₃ [BLFO (x)] ceramics with x = 0.10–0.50 and Mn‐doped BLFO (x = 0.30) ceramics with different doping contents (0.1–1.0 mol%) were prepared by solid‐state reaction method. They were crystallized in a perovskite phase with rhombohedral symmetry. In the BLFO (x) system, a composition (x)‐driven structural transformation (R3c→C222) was observed at x = 0.30. The formation of Bi₂Fe₄O₉ impure phase was effectively suppressed with increasing the x value, and the rhombohedral distortion in the BLFO ceramics was decreased, leading to some Raman active modes disappeared. A significant red frequency shift (~13 cm^?1) of the Raman mode of 232 cm^?1 in the BLFO ceramics was observed, which strongly perceived a significant destabilization in the octahedral oxygen chains, and in turn affected the local FeO₆ octahedral environment. In the Mn‐doped BLFO (x = 0.30) ceramics, the intensity of the Raman mode near 628 cm^?1 was increased with increasing the Mn‐doping content, which was resulted from an enhanced local Jahn–Teller distortions of the (Mn,Fe)O₆ octahedra. Electron microscopy images revealed some changes in the ceramic grain sizes and their morphologies in the Mn‐doped samples at different contents. Wedge‐shaped 71° ferroelectric domains with domain walls lying on the {110} planes were observed in the BLFO (x = 0.30) ceramics, whereas in the 1.0 mol% Mn‐doped BLFO (x = 0.30) samples, 71° ferroelectric domains exhibited a parallel band‐shaped morphology with average domain width of 95 nm. Dielectric studies revealed that high dielectric loss of the BLFO (x = 0.30) ceramics was drastically reduced from 0.8 to 0.01 (measured @ 10⁴ Hz) via 1.0 mol% Mn‐doping. The underlying mechanisms can be understood by a charge disproportion between the Mn⁴⁺ and Fe²⁺ in the Mn‐doped samples, where a reaction of Mn⁴⁺ + Fe²⁺→Mn³⁺ + Fe³⁺ is taken place, resulting in the reduction in the oxygen vacancies and a suppression of the electron hopping from Fe³⁺ to Fe²⁺ ions effectively.     

Effect of A‐ or B‐site doping of perovskite calcium manganite on structure,resistivity, and thermoelectric properties

Bismuth‐, lanthanum‐, and molybdenum‐doped calcium manganite (CaMnO₃, abbreviated Mn113) are synthesized by solid‐state synthesis route from their respective oxide precursors at a same doping level (x=0.05). Depending on the ionic sizes, trivalent dopants (Bi³⁺ and La³⁺) replace Ca²⁺(A site), while penta/hexavalent dopant Mo⁵⁺/Mo⁶⁺ replaces Mn⁴⁺ (B site) in the Mn113 structure. XRD of all three doped samples confirm formation of single phase. In all three samples, doping causes unit cell volume to expand, while volume expansion is maximum for the Mo‐Mn113. The transport behavior of the doped samples follows small polaron hopping mechanism. Resistivity of the doped samples depends not only on the carrier concentration but also on the effective bandwidth determined by the structural distortion introduced by the dopant ions. Bi‐Mn113 has highest resistivity at the both temperature end, while La‐Mn113 has the lowest. Thermopower is determined by the carrier concentration only and does not depend on dopant type, having value ~260 μV/K at 1000 K. At high (>800 K), S reaches a saturation value and becomes independent of T. La‐Mn113 is having highest figure of merit (zT) 0.19 at 1000 K.     

Electrical and nonlinear current-voltage characteristics of La-doped BiFeO3 ceramics

Multiferroic Bi_1-xLa_xFeO₃(x=0, 0.05, 0.1, 0.2, and 0.3) ceramics with particle sizes of ~67–19 nm were prepared by a simple co-precipitation method. The effects of La dopant on the microstructure, giant dielectric response, and electrical properties were investigated. The grain size of Bi_1-xLa_xFeO₃ ceramics significantly decreased with increasing La doping ions. The Bi_0.95La_0.05FeO₃ ceramic exhibited the highest leakage current density value. Interestingly, it strongly decreased as the concentration of La increased. The nonlinear coefficient of La doped BFO slightly decreased with increasing La. This shows a space-charge-limited conduction mechanism, which is involved in low electric field regions for all samples investigated. La substitution significantly enhanced the breakdown field. It was found that the potential barrier height at the grain boundary was slightly reduced from 0.3 to 0.16 eV by substitution of La ions. Using impedance spectroscopy analysis, except for the Bi_0.7La_0.3FeO₃ ceramic, the grain boundary resistance at room temperature was affected by dc bias, whereas the grain resistance of all samples was independent of dc bias. This result was well consistent with the variation in low-frequency dielectric constant and loss tangent value due to the effect of dc bias. These results were closely related to the existence of the interfacial polarization at the grain boundary.     

Structural,dielectric and magnetic properties of Bi–Mn doped SmFeO3

We have studied the structural, magnetic, dielectric and impedance properties of the Sm_1-xBi_xFe_1-yMn_yO₃ [SmFeO₃ (SFO), Sm_0.9Bi_0.1FeO₃ (SBFO), Sm_0.9Bi_0.1Fe_0.9Mn_0.1O₃ (SBFMO)] polycrystalline samples synthesized by solid-state reaction method. Rietveld refinement of room temperature (RT) powder x-ray diffraction pattern confirms the orthorhombic crystal structure with Pnma/Pbnm space group. The average particle size of Bi doped and co-doped (Bi–Mn) samples determined from SEM analysis are 5.6 μm and 5.2 μm, respectively. Room temperature field-dependent magnetization increases, suggesting the presence of magnetic contribution due to the Rare earth-Fe ion interaction which persists even at RT. However, with co-doping of Bi and Mn, a decrease in magnetization is observed, which corresponds to the dilution of Fe³⁺-Fe³⁺ interactions due to the presence of Mn³⁺ ions. The observed values of magnetization at 90 kOe for Bi doped sample is (2.87 emu/g) approximately two times and for codoped (0.7 emu/g) sample is nearly half of that of pristine sample (1.51 emu/g). Dielectric measurements as a function of frequency/temperature and impedance analysis using equivalent circuit model reveal grain and grain boundary contributions of SBFO (at high temperature) and SBFMO (for all temperature) samples towards the electrical properties indicating the electrically heterogeneous nature of these samples. However, for SFO sample grain contribution is dominant. Observed value of dielectric constant varies from ~10³-10⁴ with Bi–Mn doping. The conduction mechanism of the studied samples has been explained by considering Jonscher power law. Arrhenius law fitting of AC conductivity data manifests two types of conduction mechanisms in these samples. The depressing nature of the semicircular arc observed in the Nyquist plot of all the samples indicates the presence of a non-Debye type of relaxation.     

Effect of Nb substitution on magnetic,ferroelectric and photocatalytic properties of Bi0.95Sm0.05Fe1-xNbxO3 (0 ≤ x ≤ 0.1) nanoparticles

The single phase Bi_0.95Sm_0.05Fe_1-xNb_xO₃ (0 ≤ x ≤ 0.1) nanoparticles were synthesized by the sol-gel route, and the effect of Nb substitution on their magnetic, ferroelectric and photocatalytic properties were studied. X-ray diffractometry confirms a phase transformation from rhombohedral to orthorhombic with an increase in Nb substitution. The grain size decreases significantly, and the morphology of grains becomes homogeneous with the increase of Nb concentration. The maximum remnant magnetization (0.014 emu/g), coercivity (565 Oe) and polarization (0.592 μC/cm²) are observed in Bi_0.95Sm_0.05Fe_0.9Nb_0.1O₃. It has been observed that the energy band gap has been slightly reduced from 2.14 to 2.03 eV with Nb substitution, indicating an improvement of photocatalytic activity. The methylene blue degradation is used to represent the photocatalytic ability of Bi_0.95Sm_0.05Fe_1-xNb_xO₃ nanoparticles. The highest degradation efficiency (~74%) of methylene blue is obtained in Bi_0.95Sm_0.05Fe_0.93Nb_0.07O₃, which is much higher than that of Bi_0.95Sm_0.05FeO₃ (~51%) and can be attributed to the optimum particle size and the smallest energy band gap.