Structural and electrical properties of La-modified BiFeO3–BaTiO3 composites

In the present investigation, La-modified solid solutions of BiFeO₃ (BFO) and BaTiO₃ (BT) in different molar ratios [i.e., (Bi_0.5?x La _x Ba_0.5)(Fe_0.5Ti_0.5)O₃, with x = 0.0, 0.05, 0.10 and 0.15)] have been synthesized using a solid-state reaction route. Structural and electrical properties of single phase (with minor secondary phase) of BFO–BT system have been studied in details to understand their ferroelectric and other properties. Preliminary X-ray diffraction analysis confirms the formation of a new system, which is different from that of its parent compounds. Substitution of a small amount BaTiO₃ into BiFeO₃ enhances dielectric and ferroelectric responses and reduces electrical leakage or tangent loss. The ac conductivity obeys Jonscher’s universal power law. The electrical behavior of the samples was investigated by impedance spectroscopy in a wide temperature range (25–525 °C) at different frequency (1 kHz–1 MHz). The impedance spectroscopy of the materials also confirms the origin of the relaxation mechanism in the system.     

Structural, ferroelectric and piezoelectric properties of Mn-modified BiFeO3–BaTiO3 high-temperature ceramics

Mn modified BiFeO₃–BaTiO₃ (abbreviated as BFBT-Mnx%, x = 0.1, 0.3, 0.6, 0.9, 1.2) high-temperature lead-free ceramics were prepared by conventional oxide-mixed method and the effect of Mn doping on microstructure and electrical properties was investigated. The solid solutions show a single phase perovskite structure, and the content of Mn has a significant effect on the microstructure of ceramics. The addition of Mn can induce combinatory “hard” and “soft” piezoelectric characteristics due to aliovalent substitutions. In particular, x = 0.6 BFBT-Mnx% ceramic, with a Curie temperature, T _c, of ~463 °C, shows optimum piezoelectric properties of d ₃₃ = 131pC/N, k _p = 0.298. The simultaneous existence of good piezoelectric properties and high T _c makes these ceramics suitable for elevated temperature piezoelectric devices.     

Dielectric and electrical energy storage properties of BiFeO3–BaTiO3–SrTiO3 ternary bulk ceramics

Journal of Materials Science: Materials in Electronics - Recently, it is shown that the thin films of BiFeO3–BaTiO3–SrTiO3 have ultrahigh-energy storage density. However, the energy...     

Structural and physical properties of Ni–Tb–Fe–O system

A series of soft ferrites in the system Ni_1 ? xTb_xFe₂O₄ (0 ≤ x ≤ 0.2), was prepared by a standard ceramic technique. The influence of terbium content was investigated by means of X-ray diffraction, Fourier Transform Infrared (FTIR) spectroscopy and scanning electron microscopy. The X-ray diffraction analysis reveals that the samples have a cubic spinel (single phase) structure for 0 ≤ x ≤ 0.08; for x > 0.08 a small peak of orthorhombic phase (TbFeO₃) appears and becomes more conspicuous with increased terbium substitution. The lattice parameter changes in a non-linear way as a function of terbium content which may be attributed to differences in the ionic radii of the cations involved and the solubility limit of terbium ions. A gradual increase in the bulk density was observed with the increase of terbium concentration, from 5.13 g/cm³ to 5.69 g/cm³. FTIR absorption spectra of the Ni–Tb–Fe–O system were investigated in the wave number range 370–1500 cm^? 1. Each spectrum exhibited two main absorption bands, thereby confirming the spinel structure.     

Effects of Bi excess on the structure and electrical properties of high-temperature BiFeO3–BaTiO3 piezoelectric ceramics

BiFeO₃–BTiO₃(BF–BT) ceramics as a promising candidate for lead-free high-temperature piezoelectric ceramics were studied with a special emphasis on the compositional dependence of piezoelectric properties. Excess Bi was added to compensate for the evaporation of Bi³⁺ ions during sintering and this addition was found to be effective in improving the piezoelectric properties of BF–BT ceramics. The microstructure, dielectric and piezoelectric properties of excess Bi doped BF–BT ceramics were investigated. Maximum piezoelectric constant d ₃₃ = 142 pC/N and k _p = 0.302 were obtained with 0.04 Bi doping. At the same time, an enhanced Curie temperature T _c, 452 °C, was obtained. The combination of improved piezoelectric properties and increased T _c makes these ceramics suitable for elevated temperature piezoelectric devices.     

High thermally stable BiFeO3–PbTiO3–BaTiO3 ceramics with improved ferroelectric properties

High temperature (0.9-x)BiFeO₃–(x)PbTiO₃–0.1BaTiO₃ (BF–PT–BT) ceramics at MPBs (x = 0.18, 0.20 and 0.22) were synthesized by solid-state reaction technique. Well-saturated P–E loops were obtained and an enhanced ferroelectric behavior of P_r ~60 μC/cm² and E_c ~50 kV/cm was observed in 0.68BiFeO₃–0.22PbTiO₃–0.10BaTiO₃ ceramics, which was much higher than those of reported BiFeO₃–PbTiO₃-based and BiFeO₃–BaTiO₃-based ceramics. The temperature stability of the ceramics was also investigated, showing a high resistivity to thermal depoling, with a degradation temperature T_d of ~500 °C. Our results suggested that BF–PT–BT was a good lead-reduced high-temperature ferroelectric ceramics.     

Conduction mechanism and dielectric properties of BiFeO3–BaTiO3 solid solutions

The first measurements are reported for the frequency-dependent conductivity of (1?x)BiFeO₃–xBaTiO₃ (x = 0.10, 0.15 and 0.30) solid solutions in the frequency range of 10⁰–10⁶ Hz and in the temperature range of 50–300 °C. Powder X-ray diffraction confirms the formation of solid solutions. The dielectric properties were seen to improve with increasing BaTiO₃ (BT) content. The conductivity (AC and DC) measurements reveal an inverse variation of the frequency exponent ‘s’ with temperature, high density of states and thermally activated process. The calculated density of states was found to be N(E_f) = 80.2 × 10³² eV^?1 cm^?1 at 1 kHz and 50 °C for BiFeO₃–10 % BaTiO₃ (BFO–10 % BT) solid solution. The impedance spectroscopy analysis confirms the presence of grain and grain boundary affecting the conductivity. Our results provide the first unambiguous evidence of conduction in crystallite BFO–BT solid solutions through correlated-barrier-hopping model.     

Enhanced electrical properties of 0.7BiFeO3–0.3BaTiO3 lead-free ceramics obtained by optimizing the calcination temperature and time

Journal of Materials Science: Materials in Electronics - 0.7BiFeO3–0.3BaTiO3 ceramics were synthesized through the solid-state reaction method under different calcination temperatures (Tcal)...     

Dielectric and multiferroic properties of 0.75BiFeO3–0.25BaTiO3 solid solution

Solid solution 0.75BiFeO₃–0.25BaTiO₃ (BFO–25 % BT) was prepared by solid state reaction method. Powder X-ray diffraction showed the morphotropic phase boundary (MPB) with the coexistence of both rhombohedral and cubic phases due to splitting in the line at 2θ = 39.7°. Scanning electron micrographs indicated that the ceramic has compact and uniform microstructure with average grain size <3 μm. The polarization vs applied electric field analysis showed an unsaturated hysteresis loop with the remnant polarization 12.95 μC/cm² at 22 kV/cm for 0.75BiFeO₃–0.25BaTiO₃ ceramic. The calculations of diffuse parameter i.e. slope γ = 1.63 suggested a high degree of diffusion in BFO–BT lattice. The room temperature magnetic measurements confirmed the weak ferromagnetism of magnetization ~0.1 emu/gm at an applied magnetic field of H = 5 kOe for 0.75BiFeO₃–0.25BaTiO₃ ceramic. The high temperature magnetic and dielectric analysis suggested a coupling between ferroelectric and magnetic parameters near the antiferromagnetic–paramagnetic transition T_c ~ 310 °C, which was responsible for the broad frequency dependent dielectric maxima. The impedance spectroscopy and complex modulus analysis confirmed the conventional relaxor, NTCR (negative temperature coefficient of resistance), giant ferroelectricity and polydispersive non-Debye type dielectric relaxation behaviour for 0.75BiFeO₃–0.25BaTiO₃ ceramic at 170 °C on 1 kHz with activation energy 2.33 eV. The modulus analysis also confirmed the possibility of hopping mechanism for electrical transport process in material.     

Structural,optical and electrical properties of Bi2−xMnxTe3 thin films

Journal of Materials Science: Materials in Electronics - Undoped and Mn doped Bi2Te3 (x = 0, 0.05 and 0.10 at%) thin films were prepared via thermal evaporation method from their bulk alloys. X-ray...     

Structural,electrical, and magnetic properties of erbium (Er3+) substituted Cu–Cd nano-ferrites

In the present work, we reported the structural, electrical, and magnetic properties of erbium Er³⁺-substituted Cu–Cd nano-ferrites with generalized formula Cu_0.8Cd_0.2Er_xFe_2?xO₄ (where x?=?0.000, 0.0010, 0.0015, 0.002, 0.0025, 0.003), as synthesized by the Citrate-Gel Auto-Combustion. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies were carried out to investigate their microstructural and surface morphology. The XRD measurements confirm pure cubic spinel phase composition of these nanoparticles. The crystallite size ranges over 9.22–19.22 nm and it reduces with the increase in erbium Er³⁺ concentration from 0.000 to 0.003. The vibration properties were carried out by using FTIR spectrometer. The two probe measurements were used to determine DC resistivity, Curie temperature, and DC conductivity. The plot between DC electrical resistivity and temperature indicates the semiconductor behavior. At room temperature, the vibrating sample magnetometer (VSM) was used to investigate magnetic properties, and the observed values revealed the ferrimagnetic behavior with high saturation magnetization (34.24 emu/g) and high coercivity (1121.70 Oe).

     

Structural evolution and magnetic properties of mechanically alloyed metastable Fe–Ni–Zr–B system

Present investigation focuses on synthesizing metastable Fe₅₂Ni₂₆B₁₈Zr₄ (at.%) soft magnetic material through mechanical alloying. Mechanical alloying was employed to achieve nanocrystalline phase under optimized milling parameters such as milling speed, milling time, composition, etc. The effects of milling time on structural evolution and magnetic properties of Fe₅₂Ni₂₆B₁₈Zr₄ powders were analyzed using x-ray diffraction (XRD), transmission electron microscope (TEM) and vibrating sample magnetometer (VSM). Nano crystallization was achieved during the early stages of milling. The crystallite size of Fe₅₂Ni₂₆B₁₈Zr₄ was decreased with increasing milling time. The minimum grain size was found to be about 6 nm. The appreciable magnetic softening, in terms of coercivity values, observed as the milling progresses in amorphous phase at 25 h milling.     

Influence of Mn doping on structural,electrical and magnetic properties of (0.90)BiFeO3–(0.10)BaTiO3 composite

Structural, electrical and magnetic properties of chemically synthesized polycrystalline Mn doped (0.90)BiFeO₃–(0.10)BaTiO₃ composites [(0.90)BiFe_1?xMn_xO₃–(0.10)BaTiO₃ (x = 0.0, 0.03, 0.05 and 0.10)] were studied. The dielectric constant was observed to decrease when frequency was increased from 20 Hz to 1 MHz and increased with the increase in temperature from 313 to 773 K. An interesting correlation between the antiferromagnetic Neel temperature (T_N) of bismuth ferrite and temperature dependent dielectric constant was observed. The calculated values of activation energies were in the order of 0.25–0.74 eV (<1.0 eV) and decreases with an increase of Mn concentration. The variation of a.c. conductivity obeyed the Jonscher’s power law (σ _ac  ∝ ω ^s ). The observed value of exponent‘s’ were in the range 0.09 < ‘s’ < 0.78 (<1.0) for all the sample at temperature ranging from 473 to 598 K. There was a systematic increase in the value of spontaneous magnetization on increasing Mn concentration.     

Microstructure and electrical properties of Ni–Zn manganite ceramics

Nickel zinc manganite ceramics Mn_2.34−xNi_0.66Zn_xO₄ (0≤x≤1.02) were investigated using structure, microstructure and electrical property interrelationships. The resistivity increased with zinc content whereas the activation energy remained constant. The drift of resistivity under thermal constraint, commonly observed in NTC thermistors was almost nil when the zinc content was sufficiently high (x≥0.7). Homogeneous microstructures and high densities were obtained when the ceramics were prepared from fine powders. The Ni/Zn/Mn/O system prepared by ‘chimie douce’ has interesting NTC properties for industrial applications.     

Structural and durability properties of hydraulic lime–pozzolan concretes

This paper discusses the results of a suite of tests designed to assess the structural and durability characteristics of hydraulic lime–pozzolan concretes. Specifically, this paper reports on the rate of strength development, elastic modulus, linear shrinkage and rate of carbonation of four hydraulic-lime–pozzolan concretes. The purpose of this investigation was to ascertain the technical feasibility of producing high strength concretes using hydraulic lime and pozzolans as an alternative binder to Portland cement. Results have demonstrated that 28-day compressive cube strengths of 35 MPa can be attained by water-cured lime–pozzolan concretes. The results are presented alongside comparable test results for Portland-cement (CEMI) and blastfurnace cement (CIII/A) concretes. Similarities and differences in material characteristics are discussed in terms of fundamental material properties and in terms of the emergent threats and opportunities for the potential development of these novel concretes.     

Enhanced dielectric and electrical properties of three-component PMMA–NaNbO3–starch percolative composite films

Journal of Materials Science: Materials in Electronics - Three-component PMMA–NaNbO3–starch percolative composites with starch and sodium niobate (NaNbO3; NN) particles embedded into...     

Structural,dielectric, magnetic,and optical properties of Ni0.75Zn0.25Fe2O4–BiFeO3 composites

The magnetoelectric composites of spinel ferrite Ni_0.75Zn_0.25Fe₂O₄ (NZF) and BiFeO₃ (BFO) with general formula xNi_0.75Zn_0.25Fe₂O₄ + (1 ? x)BiFeO₃ (x = 0, 0.10, 0.20, and 0.30) have been prepared via hybrid processing route. Subsequently, the effects of addition of NZF on structural, dielectric, magnetic, magnetoelectric, and optical properties of BFO have been investigated, and significant enhancements have been observed in physical observables such as grain size, dielectric constant, magnetization, and polarization in ferroelectric hysteresis loops. The variation of magnetization with temperature indicates the presence of spin glass behavior along with the ferromagnetic component. The magnetoelectric coupling is found with a value of magnetocapacitance to be 4.6 % for 30 mol% addition of NZF. The optical properties of the composites are also studied using UV–Vis diffuse reflectance spectroscopy, Photoluminescence spectroscopy, and FTIR spectroscopy.