Investigation on Electrical and Magnetic Properties of Gd-doped BiFeO<Subscript>3</Subscript>

Multiferroic ceramic samples of Bi_1−x Gd _x FeO₃ (x=0, 0.05, 0.1 and 0.15) have been prepared by rapid liquid-phase sintering technique. The effect of Gd substitution on ferroelectric and magnetic properties of Bi_1−x Gd _x FeO₃ ceramics has been investigated. The results of X-ray diffraction (XRD) patterns show that the single-phase BiFeO₃ sample has a rhombohedral structure and Gd³⁺ substitution for Bi³⁺ has not affected its structure. Experimental results suggest that for Bi_1−x Gd _x FeO₃ system, the ferroelectric and magnetic properties of BiFeO₃ are improved by Gd doping and the loop area increases with the Gd content. When x=0.15, saturated ferroelectric hysteresis loop is observed at room temperature with the maximal 2Pr=1.62 μC/cm², which is about 578.6% higher than that of BiFeO₃.     

Superconducting and Normal-State Properties of (Y1?x Bi x )Ba2Cu3O7?δ (x=0.00–0.30)

The effect of Bi in (Y_1−x Bi _x )Ba₂Cu₃O_7−δ for x=0.00–0.30 has been investigated by powder X-ray diffraction method, dc electrical resistance measurements and scanning electron microscopy. The resistance versus temperature curves showed metallic behavior for samples with x≤0.20 and semiconductor-like behavior for x=0.25 and 0.30. The resistance versus temperature curves showed onset transition temperature (T _{c onset}) between 89 and 93 K and a broadening of the superconducting-transition width with increasing Bi content for all samples. T _{c onset} decreased linearly indicating a pair-breaking mechanism in T _c suppression for x=0 to 0.3. The non-systematic broadening of the transition width may be due to the inhomogeneities in the samples as Bi content was increased. No substitution of Bi for Y was observed.     

La-modification of multiferroic BiFeO<Subscript>3</Subscript> by hydrothermal method at low temperature

This study reports the effect of La doping on structural, morphological and magnetic characteristics of BiFeO₃ synthesized under mild hydrothermal conditions at 200°C for 16 h using the KOH concentration of 4 M. The as-synthesized powders of Bi_1−x La _x FeO₃ for x = 0.05, 0.10, and 0.15 were characterized by X-ray powder diffraction scanning electron microscope and the vibrating sample magnetometer. The formation mechanism of Bi_1−x La _x FeO₃ powders can be expressed by “dissolution-nucleation-crystallization” process. The magnetism of Bi_1−x La _x FeO₃ increased with increase of La content due mainly to increscent suppressing spiral magnetic structure and magnetic contribution of La.     

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.     

Characterizations of trimetallic heteronuclear Bi1−x La x [Fe(CN)6]·n(H2O) complexes and their thermal decomposition products

Heteronuclear Bi_1−x La _x [Fe(CN)₆]·nH₂O complexes were synthesized, and their crystal structures and thermal decomposition process were investigated by X-ray diffraction (XRD), thermogravimetry analysis (TGA), Auger electron spectroscopy (AES) with scanning electron microscope (SEM), and transmission electron microscopy (TEM). The crystal system of the complexes was orthorhombic having n = 4 for x = 0–0.7 and was hexagonal having n = 5 for x = 1.0. Their mixture was confirmed for x = 0.8 and 0.9. The lattice parameters for the orthorhombic increased with increasing the x value for the complexes. The single phase of trimetallic perovskite-type Bi_1−x La _x FeO₃ was obtained by its thermal decomposition at low temperature. The crystal system was hexagonal for BiFeO₃ (x = 0) and orthorhombic for x = 0.1–1.0. In the case of the decomposed perovskite sample, the lattice parameters decreased with increasing x values for Bi_1−x La _x FeO₃. The particle size was ca. 30 nm for Bi_0.2La_0.8FeO₃ obtained by thermal decomposition at 500 °C and it grew with an increase in decomposition temperature. For the Bi_0.5La_0.5FeO₃, AES showed that the elemental distributions of Bi, La, and Fe on the surface were very homogeneous for the sample decomposed at 700 °C.     

Influence of Bi substitution on microwave dielectric properties of BaO–La<Subscript>2</Subscript>O<Subscript>3</Subscript>–Sm<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiO<Subscript>2</Subscript> ceramics

The influences of Bi substitution on microwave dielectric properties of Ba₄(La_0.5Sm_0.5)_9.33Ti₁₈O₅₄ solid solutions were investigated. Dielectric ceramics with general formula Ba₄(La_(0.5−z)Sm_0.5Bi _z )_9.33Ti₁₈O₅₄, z = 0.0–0.2 were prepared by conventional solid state route. The structural analysis of all the samples was carried out by X-ray diffraction and scanning electron microscopy. The dielectric properties were investigated as a function of Bi contents using open-ended coaxial probe method in the frequency range 0.3–3.0 GHz at room temperature. Dielectric constant varies from 83 to 88 and loss tangent from 2.1 × 10⁻³ to 5.5 × 10⁻³ at 3 GHz with temperature coefficient of resonant frequency changing from 106.7 to −8.4 ppm/oC as Bi contents increases from z = 0.00–0.20. It has been found that dielectric constant and temperature coefficient of resonant frequency improve whereas loss tangent is adversely affected with increase in Bi substitution.     

The Effect of Mn Substitution on Properties of Bi1.6Pb0.4Sr2Ca2?x Mn x Cu3O y Superconductors

The effects of Mn substitution on the physical properties and structural characteristics of Bi_1.6Pb_0.4Sr₂Ca₂Cu_3−x Mn _x Oy (Bi-2223) superconductor system have been studied. For this, the samples of nominal composition Bi_1.6Pb_0.4Sr₂Ca₂Cu_3−x Mn _x Oy (x=0.00, 0.10, 0.15 & 0.20) was prepared by the solid-state reaction method. It has been found that the effects of Mn substitution favor the formation of Bi-2223 phases. The phase identification/gross structural characteristics of synthesized (HTSC) materials explored through powder X-ray diffractometer reveals that all the samples crystallize in orthorhombic structure with lattice parameters (a=5.4918 ?, b=5.4071 ?, and c=37.0608 ?) up to Mn concentration of x=0.20. The critical transition temperature (T _c) measured by standard four probe method has been found to depress from 108 K to 70 K and transport current density (J _c) has been increased from 4.67×10² to 3.52×10³ A cm⁻² as Mn content (x) increases from 0.00 to 0.20. The surface morphology investigated through scanning electron microscope and atomic force microscopy (SEM and AFM) results that voids and grains size increases as the Mn concentration increases besides the nanosphere like structures on the surface of the Mn doped Bi-2223 sample.     

Improved dielectric properties in pyrochlore type oxides: Ca3Sm3?xBixTi7Nb2O26.5 (x = 1.0, 2.0 or 3.0) by Bi substitution

Improved dielectric properties are observed in pyrochlore type oxides, Ca₃Sm_3−x Bi_xTi₇Nb₂O_26.5 (x = 1.0, 2.0 or 3.0) by Bi substitution. The dielectric constant increased with increasing Bi concentration. The dielectric constant obtained for Ca₃Bi₃Ti₇Nb₂O_26.5 is 110, whereas, without Bi (Ca₃Sm₃Ti₇Nb₂O_26.5) it is 62 at 100 kHz. The Powder X-ray diffraction analysis reveals that cubic pyrochlore type phase is formed for all the compositions. The experimental results further show that the formation of Bi substituted compounds is complete at a lower temperature than the compounds without Bi. Microstructure studies reveal that the grains formed are acicular when Bi is present in large amounts compared to cuboid grains in samples having no Bi.     

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.     

Structural, dielectric, magnetic, magnetodielectric and impedance spectroscopic studies of multiferroic BiFeO3-BaTiO3 ceramics

Polycrystalline (1−x)BiFeO₃-xBaTiO₃ (x = 0.00, 0.10, 0.20 and 0.30) ceramics have been prepared via mixed oxide route. The effect of BaTiO₃ substitution on the dielectric, ferroelectric and magnetic properties of the BiFeO₃ multiferroic perovskite was studied. From XRD analysis it revealed that BaTiO₃ substitution does not affect the crystal structure of the (1−x)BiFeO₃-xBaTiO₃ system up to x = 0.30. Improved dielectric properties were observed in the prepared system. An anomaly in the dielectric constant (?) was observed in the vicinity of the antiferromagnetic transition temperature. Experimental results suggest that in the (1−x)BiFeO₃-xBaTiO₃ system, the increase of BaTiO₃ concentration leads to the effective suppression of the spiral spin structure of BiFeO₃, resulting in the appearance of net magnetization. The dependence of dielectric constant and loss tangent on the magnetic field is a evidence of magnetoelectric coupling in (1−x)BiFeO₃-xBaTiO₃ system. The impedance analysis suggests the presence of a temperature dependent electrical relaxation process in the material, which is almost similar for all the concentrations in the present studies. The electrical conductivity has been observed to increase with rise in temperature showing a typical negative temperature coefficient of the resistance (NTCR) behaviors analogous to a semiconductor and suggests a non-Debye type of electrical relaxation.     

Synthesis of the Bi-2222 Compounds of Bi–Sr–Ln(Zr)–Cu–O (Ln = Sm,Eu, Gd,and Dy)

Bi-based superconducting compounds with the 2222 structure has been already synthesized in the Bi₂Sr₂- (Ln_1−x Ce _x )₂Cu₂O_10+y (Ln = Sm, Eu, and Gd) systems. One of the characteristics of these compounds is the existence of the fluorite-like (Ln_1−x Ce _x )₂O₂ block between two CuO₅ pyramids in the crystal structure. The tetravalent ions of Ce⁴⁺ are reported to be necessary to stabilize the 2222 structure. Recently, we have discovered that the Bi-2222 phase could be composed in the Bi₂Sr₂(Ln_2−x Zr _x )Cu₂O _z (Ln = Sm, Eu, Gd, and Dy) systems, where Zr⁴⁺ is used as a new tetravalent ion stabilizing the 2222 structure in stead of Ce⁴⁺. In the new system, nearly single 2222 phase samples have been obtained at the nominal composition of x=0.5 (Ln = Sm, Eu, and Gd) and in the range of 0.1≤x≤0.3 (Ln = Dy). Among them, the sample with Ln = Gd has the smallest resistivity at 273 K. But it is a semiconductor, and the conduction process at low temperatures is assumed to be followed by a two-dimensional VRH. The experimental results for the Gd samples with a partial substitution of Pb for Bi in the Bi₂Sr₂(Gd_2−x Zr _x )Cu₂O _z system are also reported.     

Synthesis, and study of magnetic properties, of Bi1?xCdxFeO3

Ceramic Bi_1−x Cd _x FeO₃ (x = 0.0, 0.05, and 0.1) samples were prepared by a citrate-gel method. The as-prepared compounds were calcined at 600 °C for 3 h to obtain nearly single-phase materials. The crystal structure, examined by X-ray powder diffraction (XRD) and Rietveld analysis, confirmed that the samples crystallize in a rhombohedral (space group, R-3c no. 161) structure. Magnetic measurements were carried out on the resultant powders from 300 to ~2.5 K. Magnetic hysteresis loops showed a significant increase in magnetization as a result of Cd doping in BiFeO₃.     

Substitution site effect on structural and dielectric properties of La–Bi modified PZT

Substitution site effect of (La:Bi) on the structural and dielectric properties of chemically prepared PZT system Pb_0.92 (La_1−x Bi _x ) _0.08(Zr_0.65Ti_0.35)_0.98O₃ [(a) x = 0.0, (b) x = 0.1, (c) x = 0.2, (d) x = 0.3, (e) x = 0.4 and (f) x = 1.0] have been studied. The samples were prepared by employing a simple co-precipitation technique using nitrates of lead, lanthanum, bismuth, zirconium and titanium isopropoxide. X-ray diffraction studies confirm the formation of phase pure and homogeneous ceramics of rhombohedral symmetry without bismuth addition and a tetragonal symmetry was confirmed for the compounds containing bismuth due to the presence of a doublet (200) peak in these compounds. Scanning electron micrographs shows a uniform grain distribution and the grain size and shape were modified upon bismuth addition. Increase in Bi content causes a decrease in average grain size of the material. Dielectric measurements demonstrate a diffuse type of phase transition and this diffuseness decreases with increasing Bi ion concentration. Composition (A) only showed relaxor type of behaviour. Variation of dielectric constant with temperature shows that both T _c and ε_max increases with increase of Bi concentration. This was explained on the basis of favorable B-site substitution of Bi⁺³ ions and therefore the increased strength of spontaneous polarization. Finally, it is evident that the type of substitution site also has a significant effect on the dielectric properties of the PZT system. All these results suggest that the synthesized ceramics may be suitable for device applications.     

Structural stability and sintering properties of Fe/Nb/Ti co-substituted Sr(Co0.8Fe0.1Nb0.1)1?xTixO3?δ (x?=?0.00, 0.20, 0.40) oxides

The novel Fe/Nb/Ti co-substituted Sr(Co_0.8Fe_0.1Nb_0.1)_1−x Ti _x O_3−δ (x = 0.00, 0.20, 0.40) oxides have been synthesized by the solid-state reaction method. These co-substituted strontium cobaltates possess a cubic perovskite-type structure at room temperature. Structural stability and sintering properties of the samples x = 0.00, 0.20, 0.40 were investigated by X-ray diffraction (XRD), thermogravimetry (TG), and scanning electron microscopy. The combined TG and XRD results demonstrate that the structural and chemical stability of the Fe/Nb/Ti co-substituted Sr(Co_0.8Fe_0.1Nb_0.1)_1−x Ti _x O_3−δ (x = 0.20, 0.40) oxides is improved greatly compared with the sample x = 0.00 and the Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ oxide.     

Influence of bismuth and calcium on the luminescence intensity of NaY<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Eu<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>(MoO<Subscript>4</Subscript>)<Subscript>2</Subscript> phosphors

We have studied the effect of Bi³⁺ and Ca²⁺ cation additions and partial Si, P, and V substitutions for Mo on the photoluminescence of NaY_1−x Eu _x (MoO₄)₂ scheelite-like red phosphors. The results demonstrate that the photoluminescence intensity in NaY_{1 − x} Eux(MoO₄)₂ doped with Bi³⁺ and Ca²⁺ increases with europium concentration, up to x = 0.5, without concentration quenching. When the atomic fraction of Bi³⁺ is 0.2, it has a sensitizing effect on Eu³⁺. Ca²⁺ doping to an atomic fraction of 0.45 also increases the photoluminescence intensity. Partial Si, P, and V substitutions for Mo have little effect on the photoluminescence intensity.     

Effects of Nb doping on microstructure and properties of Bi4Ti3?xNbxO12 thin films prepared by magnetron sputtering

Bi₄Ti_3−xNb_xO₁₂ ferroelectric thin films were fabricated on p-Si substrates by magnetron sputtering. The effects of Nb doping on microstructure and properties of Bi₄Ti_3−xNb_xO₁₂ films were investigated. Bi₄Ti_3−xNb_xO₁₂ films had the same structure as Bi₄Ti₃O₁₂ with smaller and more uniform grains. The dielectric and ferroelectric properties of Bi₄Ti_3−xNb_xO₁₂ films were improved by Nb doping. Bi₄Ti_3−xNb_xO₁₂ films have better dielectric and ferroelectric properties with P _r = 16.5 μC/cm², E _C < 100 kV/cm, ε _r > 290, low dielectric loss (<0.9%) and clockwise C–V curves with a memory window of 0.9 V when x = 0.03–0.045, while an excessive Nb doping would lead to bad dielectric and ferroelectric properties.     

Influence of Dy-doping on ferroelectric and dielectric properties in Bi<Subscript>1.05−x</Subscript>Dy<Subscript>x</Subscript>FeO<Subscript>3</Subscript> ceramics

Bi_1.05−xDy_xFeO₃ (BDFO) (x = 0−0.2) ceramics were synthesized by solid-state reaction method. The influence of Dy dopant on crystal structural, dielectric and ferroelectric properties was investigated. The lattice parameter and the Curie temperature of BDFO were degraded continuously with increasing contents of Dy³⁺ cations. Leakage current density, ferroelectric polarization and dielectric loss were improved by appropriate Dy doping. When x = 0.1, BDFO showed the best electric properties. At applied electric field of 53 kV/cm, the remnant polarization (2P _r ) was 12.2 μC/cm².These improvements in electric properties in BDFO ceramics could have resulted from the relatively low oxygen vacancy concentration and structural distortion.     

Fabrication and characterization of compositionally graded Bi1−x Gd x FeO3 thin films

An undoped BiFeO₃ thin film, Gd doped Bi_0.95Gd_0.05FeO₃ thin film with a constant composition, Gd up-graded doped Bi_1?x Gd _x FeO₃ and Gd down-graded doped Bi_1?x Gd _x FeO₃ thin films were successfully grown on Pt (111)/Ti/SiO₂/Si (100) substrates using a sol-gel and spin coating technique. The crystal structure, ferroelectric and dielectric characteristics as well as the leakage currents of these samples were thoroughly investigated. The XRD (X-Ray Diffraction) patterns indicate that all these thin films consist of solely perovskite phase with polycrystalline structure. No other secondary phases have been detected. Clear polarization-electric field (P-E) hysteresis loops of all these thin films demonstrate that the incorporation of Gd³⁺ into the Bi site of BFO thin film have enhanced the ferroelectric performance of pure BiFeO₃ thin film, and the Gd down-graded doped Bi_1?x Gd _x FeO₃ thin film has the best ferroelectric properties. Compared to other thin films, the optimal ferroelectric behavior of the Gd down-graded doped Bi_1?x Gd _x FeO₃ thin film results from its large dielectric constant, low dissipation factor and low leakage current.     

Control of the structure,morphology and dielectric properties of bismuth titanate ceramics by praseodymium substitution using an intermediate fuel agent-assisted self-combustion synthesis

The volatilization of bismuth (Bi) species and bismuth oxide (Bi₂O₃) leads to the presence of the oxygen vacancies (V _O⁰⁰) and consequently restrains the properties of bismuth titanate (BIT; Bi₄Ti₃O₁₂). This report presents the incorporation of different atomic ratios of praseodymium ion (Pr³⁺: x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0) into the BIT (Bi_4−x Pr _x Ti₃O₁₂) ceramics through an intermediate fuel agent-assisted self-combustion synthesis (IFSC). X-ray diffraction and Raman spectroscopy results revealed that some of bismuth ion (Bi³⁺) in the pseudo-perovskite layer containing Ti–O octahedra was substituted by Pr³⁺ ion. The substitution by ion with a smaller ionic radius caused the structure distortion and consequently resulted in the phase transformation from an orthorhombic symmetry to a tetragonal symmetry. Besides, it suppressed the volatilization of Bi and Bi₂O₃ and increased the stability of metal–oxygen octahedra in the BIT. These play a crucial role to control the crystal growth, as well as limit the V _O⁰⁰. Dense ceramic with a relative density up to 96.2% was obtained by incorporating Pr³⁺ with atomic ratio of 1.0. It exhibited high dielectric constant as 908.19 and low dissipation factor as 0.0011. The results address the possibility to control the structure, morphology and dielectric properties of BIT ceramic by incorporating Pr³⁺ ion through IFSC.     

Effects of Gd doping on the sintering and microwave dielectric properties of BiNbO<Subscript>4</Subscript> ceramics

Gd³⁺ was chosen as a substitute for Bi³⁺ in BiNbO₄ ceramics, and the substitution effects on the sintering performance and microwave dielectric properties were studied in this paper. The high temperature triclinic phase was observed only in the Bi_0.98Gd_0.02NbO₄ ceramics when sintered at 920 °C. Both bulk densities and dielectric constant (ε_r) increased with the sintering temperature, while decreased with the Gd content. The quality factor (Q) exhibited a correlation to the Gd content and the microstructures of Bi_1−x Gd _x NbO₄ ceramics. At the sintering temperature of 900 °C, Bi_0.992Gd_0.008NbO₄ ceramics exhibited microwave dielectric properties of ε_r ∼ 43.87, Q × f ∼ 16,852 GHz (at 4.3 GHz), and its temperature coefficient of resonant frequency (τ_f) was found to be near-to-zero.