Search

Polycrystalline samples of Bi0.90La0.10(Fe1-xMnx)O3 (x=0, 0.05, 0.10, 0.15, and 0.20) were prepared using a novel mechanical activation followed by a conventional solid-state reaction technique. The formation of the desired materials was confirmed using x-ray diffraction. The electrical and magnetic properties of the materials were investigated at different Mn concentrations as a function of temperature. Both dielectric constant and loss tangent increased with the increase in Mn content in the system. The grain and grain boundary contributions have been estimated using impedance spectroscopy analysis. Both grain and grain boundary conductivity increased with a rise in temperature for all Mn concentrations. The value of activation energy for both grain and grain boundary is nearly the same, and decreased with an increase in Mn concentration. There is a systematic increase in the value of magnetization on increasing Mn concentration. [ABSTRACT FROM AUTHOR]

The polycrystalline nanosize (∼60 nm) of (1-x)Pb(Fe2/3W1/3)O3–x(BiFeO3) solid solutions with a wide range of concentrations (0<=x<=0.20) were fabricated using a mechanical activation followed by a conventional solid-state reaction technique. The formation of single-phase material and better solubility of two phases [i.e., BiFeO3 (BFO) and Pb(Fe2/3W1/3)O3 (PFW)] were confirmed using an x-ray diffraction technique. Studies of frequency and temperature dependences of dielectric parameters of solid solutions have provided unique relaxor characteristics of PFW on substitution of a critical composition (i.e., 10%) of BFO in it. The loss tangent (tan δ) peaks of PFW are frequency dependent above room temperature. The sharp tan δ peaks of PFW diffuse on increasing BFO content in PFW–BFO solid solution. This exhibits the induction of relaxation properties in the nonrelaxor PFW material. An ac conductivity (σac) of solid solutions is very much dependent on the frequency and temperature. The nature of temperature dependent conductivity and values of activation energies suggest that space charge and oxygen ion vacancies play an important role in the conduction mechanism in the material. [ABSTRACT FROM AUTHOR]

In this study, the impact of Nd doping on the structural, microstructural, dielectric, ferroelectric, and transport properties of Pb (1 - x) Nd x (Fe 0.5 Nb 0.5) 1 - x / 4 O 3 (PNFN) solid solutions ( x = 0 , 0.02 , 0.04 , 0.08 , and 0.1 ) is reported. For all the solid solutions, room temperature Rietveld refined X-ray diffraction (XRD) analysis reveals the monoclinic crystal structure with Cm space group. From Field emission scanning electron microscope (FESEM) studies, the polyhedral-shaped grains are found to be homogeneously distributed. Variation of dielectric properties with temperature displays the decrease of phase transition temperature (TC) with increasing Nd content. The temperature-dependent AC conductivity follows the Arrhenius behavior and the activation energies are calculated for high temperature regions. The frequency dependent AC conductivity behavior obeys the Johnscher's power law. Impedance spectroscopy results show the impact of conductivity from the bulk (grain) and displays non-Debye type of behaviour. Electric modulus demonstrates thermally activated relaxation phenomenon in the materials. Polarization vs. electric field (P-E) loops analysis confirms the ferroelectric nature of the materials. With increase in Nd concentrations, the value of remanent polarization (2Pr) increases, on the other hand, the coercive field (2Ec) value decreases. Both of these properties are suitable for enhancement of the physical properties of the multiferroic materials. [ABSTRACT FROM AUTHOR]

Conductivity relaxation using modulus formalism has been used to explore the coupling of ionic conductivity to dielectric relaxation in polymer electrolyte based on polyethylene oxide complexed with various content of LiAsF6. The temperature dependence of conductivity followed the VTF behavior suggesting close correlation between conductivity and the segmental relaxation process in polymer electrolytes. The coupling of conductivity to the segmental process has been discussed in terms of coupling index. For all compositions studied, the coupling index was within the range of 1-11 in the temperature range of investigation, which was in agreement with the coupled systems. [ABSTRACT FROM AUTHOR]

In this report, we have investigated the effect of BaTiO3 on the preliminary structural analysis, ferroelectric phase transition and electrical properties of (1 − x) P b (F e 0.5 N b 0.5 ) O 3 − x B a T i O 3 (P F N − B T) (x = 0 , 0.025 , 0.05, and 0.1) solid solutions. Conventional solid-state reaction technique is adopted to synthesize P F N − B T solid solution. X-ray diffraction (XRD) analysis is used to study the preliminary structural analysis, which suggests the formation of the single-phase materials. The surface morphology is studied using field emission scanning electron microscope (FESEM). The temperature-dependent dielectric properties display a broad diffuse phase transition from ferroelectric to paraelectric state and the phase transition temperature was found to be decreased with an increase in BT concentrations. Ferroelectric property of the solid solutions is confirmed by the polarization vs. electric field (P–E) loops study at room temperature. Variation of AC conductivity with frequency and temperature is also studied. The addition of BT leads to a decrease in the dielectric loss and phase transition temperature. [ABSTRACT FROM AUTHOR]

Abstract: The polycrystalline samples of Sr(Fe2/3W1/3)O3 (SFW) were prepared by a high-energy ball-milling followed by solid-state reaction technique. The X-ray structural analysis showed the formation of single-phase compound in the tetragonal system, which is a distorted structure of an ideal cubic perovskite. The temperature–frequency dependence of dielectric constant and loss tangent exhibited relaxation behavior of the compound. The studies of impedance parameters (Z′, Z″) as a function of temperature and frequency have confirmed the contribution of bulk resistance of SFW. The small value of activation energy of the compound (∼0.35eV) can be explained by mixed ionic–polaronic conductivity mechanism. [Copyright &y& Elsevier]

Abstract: The effect of plasticizer (polyethylene glycol, PEG200) on dielectric and electrical properties of an ionically conducting polymer nanocomposites PEO25-NaI+5wt.% DMMT (dodecyl amine modified Na+-montmorillonite)+ x wt.% PEG200 with different value of x has been investigated. At low frequency, the variation of relative dielectric constant with frequency shows the presence of material electrode interface polarization processes. The tangent loss peaks appearing at a characteristic frequency suggest the presence of relaxing dipoles in all the samples. On addition of plasticizer, the peak shifts towards higher frequency side suggesting the speed up the relaxation time. The electrical modulus formalism is used to study the ionic relaxation processes in these composites in terms of conductivity relaxation time. Analysis of electrical modulus and dielectric permittivity functions suggest that ionic and polymer segmental motions are strongly coupled. The frequency dependence of ac conductivity follows the universal power law with a small deviation in the low frequency region due to the electrode polarization effect. [Copyright &y& Elsevier]

Abstract: The polycrystalline samples of Bi1− x Nd x FeO3 (BNFO) with x=0, 0.05, 0.1, and 0.15 were prepared by a chemical route (metal ion complex precursor solution method). A systematic change in crystal structure from rhombohedral to tetragonal on increasing Nd substitution was observed. The reduction of low-frequency dispersion in permittivity and loss pattern due to Nd substitution in BiFeO3 (BFO) was observed in its dielectric response curve. The loss tangent (tan δ) was found to be reduced on increased Nd concentration in BNFO. Dielectric anomaly near the reported Neel temperature of BFO and peaks in all the BNFO samples were observed in the permittivity vs. temperature graph. Significant opening in the room temperature M–H loop was observed on Nd substitution, which was more prominent for higher concentration of Nd. [Copyright &y& Elsevier]

The nanocrystalline fine powders (∼80 nm) of (Ba1− x La x )(Fe2/3W1/3)1− x/4O3, (BLFW) ( x = 0.0, 0.05, 0.10 and 0.15) were synthesized with a combined mechanical activation and conventional high-temperature solid-state reaction methods. Preliminary X-ray structural analysis of pellet samples (prepared from fine powders) showed formation of a single-phase tetragonal system. Detailed studies of dielectric properties (εr and tan δ) exhibit that these parameters are strongly dependent on frequency, temperature and La composition. The La-substitution increases the dielectric constant and decreases the tan δ up to 10% substitutions of La at the Ba-site, and then reversed the variation, and hence this composition is considered as a critical composition. This observation was found valid for structure, microstructures, dielectric constant, electrical conductivity, J– E characteristics and impedance parameters also. Like in other perovskites (PZT, BZT), La substitution plays an important role in tailoring the properties of Ba(Fe2/3W1/3)O3 ceramics. [ABSTRACT FROM AUTHOR]

Abstract: The polycrystalline samples of La-modified Bi(Sc1/2Fe1/2)O3 (i.e., (Bi1−x La x )(Sc1/2Fe1/2)O3) were prepared using a solid-state reaction technique. The formation of single-phase compound was checked with an X-ray diffraction (XRD) technique. A small amount of La-substitution (0≤ x ≤0.15) at the Bi site does not change the crystal structure of Bi(Sc1/2Fe1/2)O3. Detailed studies of dielectric properties (i.e., dielectric constant, loss tangent and ac conductivity) showed significant effect of La doping on these properties. High dielectric constant with relatively low loss tangent and electrical conductivity of the mixed-type (i.e., space charge and oxygen ion vacancies) are some of the special features of the La-modified Bi(Sc1/2Fe1/2)O3 compounds. [Copyright &y& Elsevier]

Abstract: The polycrystalline nanoceramics (∼60nm) of Ca(Fe2/3W1/3)O3 (CFW) were synthesized by mechanochemical and solid-state reaction techniques. Preliminary X-ray structural analysis of CFW suggested the formation of single-phase compound in tetragonal crystal system (distorted structure of ideal perovskite). The large distortion (∼16%) is supported by a large deviation of tolerance factor t=0.86 from unity (for ideal perovskite). The SEM micrograph shows the polycrystalline nature of the sample with different grain sizes, which are inhomogeneously distributed through the sample surface. Detailed studies of dielectric and impedance properties of the material in a wide range of frequency (1kHz–1MHz) and temperatures (300–630K) show that these properties are strongly temperature and frequency dependent. The nature of variation of AC conductivity exhibits a progressive increase in AC conductivity on increasing temperature. The oxygen vacancies, space charge and mobile charge carriers play an important role in relaxation and conduction process. The relaxation process in the material was found to be of non-Debye type. [Copyright &y& Elsevier]

Abstract: A nanocomposite electrolyte comprising a polymer–salt complex (PEO25–NaClO4) and an organically modified sodium montmorillonite (Na-MMT) has been prepared using tape casting technique. The effect of clay concentration on structural, microstructural and electrical properties has been investigated. X-ray diffraction (XRD) analysis confirmed the formation and structure of the nanocomposite. FTIR analysis suggested a clear evidence of polymer–ion–clay interaction indicated by the changes appearing in the ν(ClO4 −) and ν(C–O–C) bands as a function of the clay concentration. The surface properties and microstructure has been studied using atomic force microscopy (AFM) technique. Complex impedance spectrum (CIS) shows the existence of bulk and grain boundary effects in the nanocomposite films. The temperature dependence of electrical conductivity obeys VTF pattern of variation. [Copyright &y& Elsevier]

Abstract: A layered perovskite ceramic oxide, NaNdTiO4, has been prepared by a standard solid-state reaction technique. Compound formation and phase identification has been confirmed by X-ray diffraction (XRD) studies. The material has been found to contain NaNdTiO4 as the predominant phase together with a minor impurity phase of Na2Nd2Ti3O10. Sample microstructure, observed through scanning electron microscopy, appears to be polycrystalline with shape anisotropy. Complex impedance analysis of the sample has indicated (i) the presence of grain boundary effects at temperatures above 200°C; (ii) negative temperature coefficient of resistance (NTCR) effect; and (iii) evidence of multiple electrical relaxation phenomena in the sample. The sample impedance behavior has been explained in terms of brick-layer model. The impedance measurements have shown the evidence of grain boundary conduction and lowering of barrier to the motion of charge carriers with rise in temperature. Electrical conductivity (σ dc) as evaluated from complex impedance spectrum, shows a large jump in the value at higher temperatures (∼1.66 × 10−4 Scm−1 at 550°C) when compared to the room temperature conductivity value (∼4.5 × 10−9 Scm−1). It has been attributed to the weakening of the interaction between the interlayer sodium ion and the perovskite layer. The results of ac conductivity as a function of frequency are also discussed. [Copyright &y& Elsevier]

A new plasticized composite polymer electrolyte (PCPE) based on poly(ethylene oxide)–NaClO4 dispersed with a ceramic filler (SnO2) and plasticized with polyethylene glycol (PEG200) is reported. The effect of plasticizer concentration on changes in structure/microstructure and their correlation with physical properties has been investigated and reported. A substantial enhancement in the electrical conductivity, by two orders of magnitude at room temperature, of the PCPE has been noticed when compared with that of composite polymer electrolyte (CPE) films without any plasticizer. This enhancement in electrical conductivity of the PCPE films agrees well with the changes in the local microstructure/structure on plasticizer addition. Grain boundary resistance (Rgb) and glass transition temperature (Tg) have been observed to decrease with increasing concentration of PEG200. Plasticizer addition has resulted in the suppression of crystallinity as observed from differential scanning calorimetry (DSC) and X-ray diffraction (XRD) studies. The DSC results indicate enhancement in the volume fraction of the amorphous phase, which appears to be consistent with the broadening in the polymer host peaks observed in X-ray diffractograms. The improvement in electrical conductivity has been achieved without any sharp deterioration in the thermal, electrochemical or mechanical stability of the PCPE thin films. These observations have been interpreted in terms of the action of plasticizer as a diluent/co-solvent. [Copyright &y& Elsevier]

Doping of suitable metal ions in ferroelectric oxides modifies the physical properties and can induce additional functionalities. Here, we present a detailed study on the effects of Sm concentration on the structural, dielectric, ferroelectric, and piezoelectric properties of ((K0.5Na0.5)1−3xSmx)NbO3 (KNSN) (0.00 ≤ x ≤ 0.02) ceramics. X‐ray diffraction and Raman spectroscopic analysis indicate that KNSN ceramics exhibit the single‐phase orthorhombic (Amm2) structure for x = 0.00 and the coexistence of orthorhombic and tetragonal (Amm2 + P4mm) structure for the composition range 0.005 ≤ x ≤ 0.02. The tetragonal phase fraction increases with an increase in Sm concentration. We observed dielectric relaxation behavior in KNSN at orthorhombic to tetragonal (TO–T) phase transition temperature, and its origin can be attributed to the structural heterogeneity at the inter‐ferroelectric phase boundary. Increasing Sm concentration leads to the broadening of the ferroelectric phase transition peaks. Further, the structural heterogeneity of the ceramics was seen from the slope of the dielectric constant versus log frequency and central peak behavior of Raman spectra at room temperature (RT). The study reveals that x = 0.005 shows maximum dielectric constant (Ɛr = 583), remanent polarization (2Pr = 57.02 μC/cm2), and piezoelectric coefficient (d33 = 94 pC/N) at RT and is associated with increased local structural heterogeneity due to Sm doping. [ABSTRACT FROM AUTHOR]

Multiferroic composites consisting of a single-phase multiferroic [0.6(PbZr0.53Ti0.47O3)-0.4(PbFe0.5Ta0.5)O3] as a matrix and a magnetostrictive phase (Co0.6Zn0.4Fe1.7Mn0.3O4) dispersed in the matrix are fabricated via hybrid synthesis technique. The structure and surface morphology studies using x-ray diffraction and field emission scanning electron microscopy techniques indicate the formation of 3-0 type particulate composites. Coexistence of soft-magnetic behavior and ferroelectric characteristics are confirmed for composites from magnetization vs magnetic field (M–H) and polarization vs electric field (P–E) measurements, respectively. Magneto-dielectric (MD) measurement shows significant changes in the dielectric properties with the application of a magnetic field, indicating the existence of strong MD behavior. The biquadratic nature of magneto-electric (ME) coupling is described by the Landau free energy equation arising from the strain transfer at the interfaces between the constituent phases. The direct magneto-electric voltage coefficient measurement also confirms very strong coupling between ferroelectricity and magnetism and supports the strain-mediated magneto-electric effect in composites. The Φ = 0.3 composite exhibits the maximum ME coefficient of 20.72 mV/cm Oe with MS = 24.62 emu/g, HC = 59.66 Oe, and piezoelectric coefficient value d33 = 19 pC/N. The strong magneto-electric effect along with low dielectric loss at room temperature in these composites suggests their suitability for multifunctional magneto-electric device applications such as magnetic sensors, etc. [ABSTRACT FROM AUTHOR]

In this article, we present the results of low-temperature dielectric, magnetic and magnetodielectric properties of BiFeO3 nanoceramics prepared by auto-combustion method. Rietveld refinement results of X-ray diffraction data show that sample crystallizes in single-phase rhombohedral perovskite structure with R3c (No. 161) space group. The average crystallite size was found to be ≈ 600 Å from Williamson–Hall analysis. The temperature-dependent dielectric data have been presented in permittivity and modulus formalism to understand the relaxation dynamics. Three non-Debye-type relaxation processes were observed in the experimental window (173 to 423 K), which are explained using Kohlrausch–Williams–Watts (KWW) decay function. The temperature variation of relaxation times obeys Arrhenius's behaviour. The anomaly observed in the temperature dependence of relaxation times data near 240 K corresponds to the magnetic transition of BiFeO3. We found that single ionized oxygen vacancies with activation energy ranging from 0.4 to 0.8 eV are involved in the relaxation process. A crossover from AFM/PM to weak ferromagnetic ordering is observed at low temperature. The variation of capacitance with an applied magnetic field shows a hysteresis effect. The magnetocapacitance (MC%) changes by 3% at a magnetic field of 2 T for 200 kHz, indicating an intrinsic bulk magnetocapacitance effect in the ceramics. Hence, the above findings highlight the significance of the material as a potential candidate for device applications. [ABSTRACT FROM AUTHOR]

Ferroelectric materials exhibiting switchable and spontaneous polarization have strong potential to be utilized in various novel electronic devices. Solid solutions of different perovskite structures induce the coexistence of various phases and enhance the physical functionalities around the phase coexistence region. The construction of phase diagrams is important as they describe the material properties, which are linked to the underpinning physics determining the system. Here we present the phase diagram of (K0.5Na0.5NbO3)–(Ba0.5Sr0.5TiO3) (KNN-BST) system as a function of composition and their associated physical properties. Lead-free (1 − x)KNN–xBST (0 ≤ x ≤ 0.3) solid solution ceramics were synthesized by conventional solid-state reaction technique. The X-ray diffraction and Raman spectroscopic studies indicate composition-dependent structural phase transitions from an orthorhombic phase for x = 0 to orthorhombic + tetragonal dual-phase (for 0.025 ≤ x ≤ 0.15), then a tetragonal + cubic dual-phase (x = 0.2) and finally a cubic single phase for x ≥ 0.25 at room temperature (RT). Among these, the orthorhombic + tetragonal dual-phase system shows an enhanced value of the dielectric constant at room temperature. The phase transition temperatures, orthorhombic to tetragonal (TO-T) and tetragonal to cubic (TC), decrease with the increase in BST concentrations. The ferroelectric studies show a decrease of both 2Pr and EC values with a rise in BST concentration and x = 0.025 showed a maximum piezoelectric coefficient. [ABSTRACT FROM AUTHOR]

Here, we have studied the phase transition and magneto-electric properties of a 70 wt. % Pb(Fe0.5Nb0.5)O3–30 wt. % Co0.6Zn0.4Fe1.7Mn0.3O4 (70 wt. % PFN–30 wt. % CZFMO) multiferroic composite that exhibits a maximum magneto-electric (ME) coefficient of 26.78 mV/cm Oe at room temperature. Raman analysis confirms the formation of composite and development of strain with the shifting of Raman modes. The local symmetry breaking of end members of the composite is observed by the splitting of Raman modes. The first-order derivative of magnetization with temperature (dM/dT vs T) shows anomalies across 140 K due to the PFN phase, whereas the anomaly around 250 K is due to the spin glass transition of the CZFMO phase. The magnetization vs magnetic field (M–H) study at different temperatures reveals the existence of superparamagnetic behavior above 300 K. The temperature-dependent dielectric behavior of the composite shows an anomaly around ferroelectric phase transition (Tm) for the PFN phase along with the broad relaxation peak arising due to the CZFMO phase. The linear behavior of magnetocapacitance (MD%) with the square of magnetization (M2) suggests the existence of biquadratic ME coupling. The ME study on the composite suggests the existence of both direct and converse ME effects. [ABSTRACT FROM AUTHOR]

Abstract Varying the substrate temperature changes structural and magnetic properties of spinel ferrite Ni 0.65 Zn 0.35 Fe 2 O 4 (NZFO) thin films. X-ray diffraction of films grown at different temperature display only (004) reflections, without any secondary peaks, showing growth orientation along the c-axis. We find an increase in crystalline quality of these thin films with the rise of substrate temperature. The surface topography of thin films grown at different growth temperatures reveal that these films are smooth with low roughness; however, the thin films grown at 800 °C exhibit lowest average and root mean square (rms) roughness among all thin films. We find iron and nickel to be more oxidized (greater Fe3+ and Ni3+ content) in films grown and annealed at 700 °C and 800 °C, compared to those films grown at lower temperatures. The magnetic moment is observed to increase with an increase of substrate temperature and all thin films possess high saturation magnetization and low coercive field at room temperature. Films grown at 800 °C exhibit a ferrimagnetic–paramagnetic phase transition well above room temperature. The observed large magnetizations with soft magnetic behavior in NZFO thin films above room temperature suggest potential applications in memory, spintronics, and multifunctional devices. Highlights • Highly c-axis oriented NZFO thin films were grown by PLD technique. • Varying the substrate temperature changes structural and magnetic properties. • All thin films exhibit high Ms, low Mr and low Hc at room temperature. • The M s is found to be increased with increase of substrate temperature. • Thin films grown at 800 °C exhibit a ferrimagnetic Tc ∼716 (±10) K. [ABSTRACT FROM AUTHOR]

Magnetoelectric (ME) composite thin films are promising candidates for novel applications in future nanoelectronics, spintronics, memory, and other multifunctional devices as they exhibit much higher ME coupling and transition temperatures (Tc) than well-known single phase multiferroics discovered to date. Among the three types of multiferroic composite nanostructures, (2–2) layered and (1–3) vertically aligned composite nanostructures exhibit comparatively smaller ME coupling due to different shortcomings that restrict their use in many applications. Here, we study the morphological, piezoresponse force microscopic (PFM), ferroelectric, magnetic, and magnetodielectric properties of 0–3 [magnetic nanoparticles (0) homogeneously distributed in ferroelectric matrices (3)] multiferroic composite thin films. The Pb(Fe0.5Nb0.5)O3 (PFN)–Ni0.65Zn0.35Fe2O4 (NZFO) particulate composite films were synthesized by pulsed laser deposition. These particulate composite thin films are completely c-axis oriented with very low surface roughness. We observed magnetic and ferroelectric Tc above room temperature (RT) for all composite thin films. The PFN–NZFO 0–3 composites exhibit large polarization, high saturated magnetization with low coercive field, and low dielectric loss along with magnetodielectric coupling at RT. These nanocomposites might be utilized in next generation nano/microelectronics and spintronic devices. [ABSTRACT FROM AUTHOR]

With the rapid development of new device miniaturization technology, there is invigorated interest in magnetic nanostructures for potential application in novel multifunctional devices. In continuation to our search for a suitable magnetic material having Curie temperature (Tc) well above room temperature for multifunctional applications, we have studied the dielectric, optical, magnetic, and resistance switching characteristics of Ni0.65Zn0.35Fe2O4 (NZFO) thin films. The observation of only (004) reflection in the X-ray diffraction patterns confirms the c-axis orientation and high quality growth of NZFO thin films. The presence of mixed valences of Fe2+/Fe3+ cations is probed by X-ray photon spectroscopy, which supports the cationic ordering-mediated large dielectric response. Our investigations reveal NZFO to be an indirect band gap material (~1.8eV) with a direct gap at ~2.55eV. These nanostructures exhibit high saturation magnetization and a low coercive field with a ferrimagnetic-paramagnetic phase transition of ~713K. Magnetic force microscopy studies revealed the stripe-like domain structure of the investigated thin films. In addition, these thin films exhibit reliable and repeatable unipolar resistive switching characteristics. The observed high dielectric permittivity with low loss tangent, large magnetization with soft magnetic behavior, striped magnetic domain structure and reliable resistance switching in NZFO thin films above room temperature suggest potential application in memory, spintronics, and multifunctional devices. [ABSTRACT FROM AUTHOR]

This manuscript presents a systematic study of conductivity and dielectric relaxations in the solid solution of (BiFeO3)1-x -(YMnO3)x for compositional range (0.0 ≤ x ≤ 0.2) as function of frequency, temperature, and magnetic field. The samples have been synthesized by combustion method. The thermal activations of dc-conductivity and relaxation time obey Arrhenius behavior for, x = 0.0, 0.025, 0.05 but follow variable range hopping of small polarons above, x ≥ 0.075 with activation energy 0.45 eV. The compositional time-temperature superposition of dielectric modulus data suggests that conduction mechanism changes with composition. The bulk capacitance decreases with increase in magnetic field. [ABSTRACT FROM AUTHOR]

Spinel ferrites have been widely studied due to their remarkable properties such as high saturation magnetisation, large magnetic permeability, and high electrical resistivity. Among the oxides-based magneto strictive spinel ferrite, CoFe2O4 (CFO) possess the highest value of absolute magnetostriction coefficient (–110 ppm). But CFO has the disadvantage of large magnetic anisotropy and high coercivity. Therefore, doping of zinc (Zn) at Co-site of CFO is reported to reduce the magnetic coercivity and increases the resistivity (108Ω) keeping the magnetostriction coefficient with a sizable value. Also, substitution of Zn for Co in CFO reduces magnetic anisotropy. So, in view of this we have prepared Zn modified CFO compound: Co0.9Zn0.1Fe2O4 using sol-gel combustion technique. The room temperature (RT) XRD patterns indicate the formation of single-phase material without appearance of any impurity phases within the detection limit of X-ray diffractometer. The Rietveld refinement on the RT XRD pattern of CZFO sample was carried out using cubic crystal structure with space group Fd-3m. A good agreement between the experimental and the fitted data has been observed. The average crystallite size for the composition was calculated from the XRD patterns using Williamson–Hall method. Scanning electron micrographs displays homogeneous distribution of grains throughout the sample microstructure with the presence of minute amount of pores. The dielectric and electrical properties were studied as function of frequencies at different temperatures. Complex impedance spectroscopic technique study on this sample suggests existence of non-Debye type dielectric relaxation behaviour. [ABSTRACT FROM AUTHOR]

We report the mechanism to enhance the dielectric and ferroelectric behavior of polymer-ceramic composites through surface hydroxylation of 0.5Ba(Zr 0.2 Ti 0.8)O 3 -0.5(Ba 0.7 Ca 0.3)TiO 3 (BZT-BCT) ceramic filler-particles embedded in PVDF-HFP copolymer matrix. Varying the hydroxylated h-(BZT-BCT) filler particle-content (φ = 0–40 wt%) in PVDF-HFP copolymer matrix, composite films (of ~75 μm thickness) were prepared. We observed that, with an increase in filler content up to an optimum concentration of 15 wt% , a microstructure with gradually denser particle-arrangement and enhanced particles-polymer surface interaction is exhibited, which leads to improved dielectric and ferroelectric behavior. The energy storage density (728 mJ/cm3 at an electric field of 750 kV/cm) of the composite with 15 wt% of h-(BZT-BCT) is found to be much higher than those of the pure BZT-BCT sample, pure PVDF-HFP copolymer and their composites. Our work demonstrates the method of enhancing the functional properties through a suitable microstructure of composite materials with surface-hydroxylation of filler particles. • Ferroelectricity in virgin and hydroxylated (h-) BZT-BCT ceramic/PVDF-HFP copolymer composites is studied. • A 15 wt% concentration of h-(BZT-BCT) filler particles enhances packing density of composite by minimizing voids. • High packing density enhances interfacial interaction between h-(BZT-BCT) fillers and PVDF-HFP polymer. • Hydroxyl (–OH) ions on h-(BZT-BCT) particles facilitates formation of electroactive β-phase of PVDF-HFP. • Our work demonstrates a method to improve ferroelectricity and energy storage density of ceramic/polymer composites. [ABSTRACT FROM AUTHOR]

Abstract: Structural, microstructural and electrical properties of lanthanum-modified sodium bismuth titanate (Na0.5Bi0.5TiO3) (NBT) ceramics were investigated. X-ray diffraction (XRD) analysis of the prepared materials confirmed the formation of the compounds with rhombohedral crystal system. The nature of scanning electron micrographs of the compounds showed (i) the uniform distribution of grains on the sample surface with high density and (ii) reduction of grain size on La substitution at the (Na of NBT. Detailed studies of dielectric and impedance properties of the materials, carried out in the frequency range of 102–106 Hz at different temperatures (room temperature to 500°C), have provided many interesting properties. The dielectric constant at transition temperature was found to be decreased with increase of broadening of the dielectric peak on increasing La content in the sample. The transition temperature (T m) shifted to higher temperature side on addition of La (up to 6%), whereas the reverse trend was observed for higher concentration of La (i.e. 8%). The depolarization temperature (T d) of La-modified NBT compounds was found to be smaller than that of pure NBT. The tangent loss was also found to be decreased on the incorporation of La into NBT. The ac conductivity of the La-modified NBT obeyed the double power law behavior. Complex impedance spectroscopy has been carried out for better understanding of relaxation process and correlations between the microstructure–electrical properties of the materials. [Copyright &y& Elsevier]

Abstract: Li(Ni0.8Co0.1Mn0.1)O2 cathode materials were synthesized by solid-state reaction route. Single-phase layer structure with hexagonal unit cell having symmetry was obtained and the average particle size was around 6μm. Electrochemical studies showed single redox reaction and a maximum charging capacity of ∼140mAhg−1 was obtained. Ex situ structural studies by X-ray diffraction and Raman scattering at various stages of charging and discharging showed that the host layered structure is maintained throughout the electrochemical lithiation–delithiation processes in the 3–4.5V range with systematic change in the lattice parameters. First discharge capacity was 132mAhg−1 and the capacity retention was ∼86% after 20 charge–discharge cycles. [Copyright &y& Elsevier]

Ferroelectric ceramic–polymer composites consisting of Poly Vinyledine Fluoride–Hexa Fluoro Propylene (PVDF-HFP) as polymer host and 0.5Ba(Zr0.2Ti0.8)O3−0.5(Ba0.7Ca0.3)TiO3 (BZT-BCT) ceramics as filler were prepared using solution casting technique. These composites are characterized for structural, microstructural, vibrational, optical, dielectric and ferroelectric properties at various experimental conditions. The electroactive β phase fraction (observed from XRD and FTIR analysis) increases as the filler concentration increases up to 20 wt% of BZT-BCT and above that its value decreases. FTIR results were analyzed to understand the mechanism of enhancement of β phase by the interaction between negatively surface charged ions of filler with the CH2 dipole of polymer matrix. UV–visible spectroscopy also employed to confirm polymer–ceramic filler interaction. Variation of the dielectric constant with different filler concentrations is explained using the percolation theory. Finally, the interplay between the functional properties and the β phase is discussed in detail. [ABSTRACT FROM AUTHOR]

We report systematic studies on crystal structure and magneto-dielectric properties of (1-x) BiFeO3-x DyMnO3 (0.0⩽x⩽0.2) nanoceramics synthesized by auto-combustion method. Rietveld refinement of X-ray diffraction data indicates a structural transition from R3c to R3c + Pn21a at x=0.1. Field emission scanning electron micrographs display a decrease in grain size with increase in x. The presence of dielectric anomalies around antiferromagnetic transition temperature implies the magnetoelectric coupling. Dielectric measurements showed decrease in magnetic ordering temperature with increasing x in agreement with differential scanning calorimetry results. A significant increase in magnetization has been found with increasing DyMnO3 substitution. Magnetoimpedance spectroscopy reveals a significant change (∼18%) in dielectric permittivity at H=2T for x=0.2. [ABSTRACT FROM AUTHOR]

Multiferroic composites are promising candidates for magnetic field sensors, next-generation low power memory and spintronic devices, as they exhibit much higher magnetoelectric (ME) coupling and coupled ordering parameters compared to the single-phase multiferroics. Hence, the 3-0 type particulate multiferroic composites having general formula (1 − Φ)[PbFe0.5Nb0.5O3]-Φ[Co0.6Zn0.4Fe1.7Mn0.3O4] (Φ = 0.0, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 1.0, (1 − Φ) PFN-ΦCZFMO) were prepared using a hybrid synthesis technique. Preliminary structural and microstructural analysis were carried out using XRD and FESEM techniques, which suggest the formation of 3-0 type particulate composite without the presence of any impurity phases. The multiferroic behaviour of the composites is studied with polarization versus electric field (P-E) and magnetization versus magnetic field (M-H) characteristics at room temperature. The nature of ME coupling was investigated elaborately by employing the Landau free energy equation along with the magneto-capacitance measurement. This investigation suggests the existence of biquadratic nature of ME coupling (P2M2). The magneto-electric coupling measurement also suggests that strain mediated domain coupling between the ferroelectric and magnetic ordering is responsible for the magneto-electric behaviour. The obtained value of direct ME coefficient 26.78 mV/cm-Oe for Φ = 0.3, found to be higher than the well-known single-phase materials and polycrystalline composites. [ABSTRACT FROM AUTHOR]

We report the crystal structure, dielectric, transport, and magnetic properties of Ni0.65Zn0.35Fe2O4. Rietveld refinement results of X-ray diffraction patterns confirm the phase formation of the material with cubic crystal structure (Fd3m). The frequency dependent ac conductivity behavior obeys the Jonscher's power law and is explained using the jump relaxation model. The observed behavior of temperature dependent bulk conductivity is attributed to the variable-range hopping of localized polarons. The correlation of polaron conduction and high permittivity behavior of NZFO is established on the basis of long range and short range conduction mechanisms. The complex impedance spectra clearly show the contribution of both grain and grain boundary effect on the electrical properties. [ABSTRACT FROM AUTHOR]

We report the crystal structure, magnetic, ferroelectric, dielectric, and magneto-dielectric properties of [Pb(Fe0.5Nb0.5)O3](1-x)[Co0.65Zn0.35Fe2O4]x: (x = 0.1, 0.2, 0.3, and 0.4) composites. Rietveld refinement results of X-ray diffraction patterns confirm the formation of these composites for all x values. All the composites show well-saturated ferroelectric and ferromagnetic hysteresis (multiferroic-composite behavior) at room temperature. With increase in Co0.65Zn0.35Fe2O4 (CZFO) content an increase in saturation magnetization, and decrease in saturation polarization, remanent polarization, and dielectric constant are observed. The ferroelectric phase transition temperature increases with increase in CZFO content. All of the compositions undergo second-order ferroelectric phase transitions, which can be explained by Landau-Devonshire theory. The recoverable energy density (∼0.20 to 0.04 J/cm3) and charge-curve energy density (∼0.84 to 0.11 J/cm3) decrease with increase in the CZFO content. The room-temperature magneto-dielectric measurements provide direct evidence of magneto-electric coupling via strain at room temperature. [ABSTRACT FROM AUTHOR]

We report the crystal structure, dielectric, magnetic, and magneto-electric properties of (1-x) BiFeO3-xYMnO3 (0.00 ≤ x ≤ 0.2) multiferroic nanoceramics prepared by auto-combustion technique. YMnO3 substitution is found to induce a structural phase transition from R3c to R3c+Pbnm after x ≈ 0.1 using Rietveld refinement technique. Field emission scanning electron micrographs show decrease in grain size with increase in YMnO3 content. The dielectric permittivity and loss tangent are found to be increased with composition x. The anomalies noticed from the temperature dependent dielectric analysis reveal the signature of magneto-electric coupling in the system. A decrease in magnetic ordering temperature as a function of composition is found from dielectric study. At room temperature, the dielectric permittivity of all the YMnO3 modified samples decrease with increasing magnetic field. The maximum value of magneto-electric coupling coefficient ([variant_greek_epsilon](H)-[variant_greek_epsilon](0))/[variant_greek_epsilon](0) is found to be ∼ -5.5% at H = 2 T for x = 0.2. The behaviour of the magnetic hysteresis loop observed at room temperature suggests the suppression of space modulated spin structure. [ABSTRACT FROM AUTHOR]

The acrylamide polymer gel template method has been adopted to synthesize single phase Dy1–xGdxMnO3 (DGMO, x= 0, 0.05, 0.1, 0.15, 0.2) ceramics. The Rietveld refinement of x-ray diffraction patterns recorded at room temperature suggests that DGMO ceramics are stabilized in an orthorhombic crystal structure with a Pnma space group. Gd3+ cations play an important role in stabilizing the orthorhombic phase and the unit cell volume increases with x. We report the phonon spectra of pure and Gd-substituted DyMnO3 (DMO) and their mode assignments. Raman modes are softened with x due to the relaxation in the stiffness constants upon the increase in the volume of the unit cell. The magnetic transition temperatures corresponding to TN(Dy) and Tlock decrease with the increase in Gd concentration as inferred from the temperature dependent magnetization data (M–T curve). The magnetization value increases below TN(Dy) with the increase in the Gd concentration as observed from the M–T plot. The magnetic hysteresis loop is fitted to extract ferromagnetic and antiferromagnetic/paramagnetic contributions for each composition x. Fittings of M–H loops indicate the increase in the magnetic contribution below TN(Dy) upon increasing the Gd dopant concentrations, while that decreases above TN(Dy). The temperature dependent specific heat data identifies these magnetic transition temperatures TN(Dy), Tlock and TN(Mn). Furthermore, magnetic field dependencies on TN(Dy), Tlock and TN(Mn) are studied in an elaborate manner. Both DMO and DGMO samples are found to be viable candidates for magnetic refrigeration applications in cryogenic temperature region. [ABSTRACT FROM AUTHOR]

Highlights • Acrylamide polymer gel template method has been used to prepare single phase DyMnO 3. • Heat capacity measurement shows three transitions due to T N (Dy), T lock and T N (Mn). • Magnetic field strongly affect T N (Dy) and T lock as observed in heat capacity data. • The magnetic study reveals the presence of two transitions due to T N (Dy) and T lock. • Increase in weak ferromagnetic behaviour with decrease in temperature. Abstract Single phase polycrystalline DyMnO 3 (DMO) was synthesized using acrylamide polymer gel template method. We report the structural, magnetic, specific heat and dielectric properties of DMO over wide experimental conditions. Room temperature XRD pattern shows the formation of singe phase material without any impurity. The magnetic properties such as magnetization versus temperature (M vs. T) and magnetization versus magnetic field (M vs. H) were studied around the transition temperatures region. The temperature dependent magnetization data suggest two phase transitions corresponding to the lock-in temperature below which ferroelectric ordering exist (around 19 K; T lock) and antiferromagnetic (AFM) ordering of Dy spin (around 8 K; T N (Dy)). The magnetic hysteresis obtained were fitted to extract weak ferromagnetic (FM) and antiferromagnetic/paramagnetic (AFM/PM) contribution to the magnetic data. The order of magnetic transitions were analyzed from Arrott plot. The temperature dependent specific heat measurement shows all three phase transitions corresponding to (i) AFM ordering of Mn spin (around 38 K; T N (Mn)), (ii) T lock transition and (iii) T N (Dy) transition. The effect of magnetic field to the transitions were studied using specific heat capacity measurement. The peak intensity of T N (Dy) decreases on the application of magnetic field whereas peak intensity of T lock increases with increase in magnetic field in specific heat measurement. Further the third anomaly, T N (Mn) remains more or less unaffected by the application of magnetic field. The intrinsic dielectric behaviour of the material was observed up to 160 K, above this temperature there is large increase in dielectric value due to the contribution from Maxwell- Wagner polarization. [ABSTRACT FROM AUTHOR]

Free standing and flexible ferroelectric ceramic-polymer composites (PVDF+ ϕ wt.% of BNBT (0.94Na 0.5 Bi 0. 5 TiO 3 -0.06BaTiO 3)) with 0–3 connectivity were synthesized by solution-casting technique. Composite nature and homogeneous distribution of ceramic filler particles in PVDF were confirmed with x-ray diffraction and scanning electron microscopic analysis. The intensity ratio of β-phase with respect to α–phase i.e., I 20.2° /I 18.4° (obtained from XRD analysis) and the fraction of electro-active beta phase i.e., F(β)% (obtained from FTIR analysis) are enhanced with increase in filler concentrations and peaked for 35 wt% of the ceramic filler. An enhancement of the % of crystallinity (calculated from XRD analysis) has been observed with increase in the filler concentrations. The increase of the fraction of β-phase has been explained on the basis of ion (negatively charged surface ion of the ferroelectric ceramic filler) -dipole (-CH 2 dipole of the polymer matrix) interactions, as evidenced from FTIR and UV-VIS absorbance spectra. Relative dielectric permittivity (dielectric constant) and ferroelectric polarization were found to be highest for the composite with 35 wt% of ferroelectric ceramic filler. Percolation theory has been successfully employed to explain the observed trend in the dielectric properties with the compositional variation. Significant enhancement in the electro active β-phase has been correlated with the improved dielectric and ferroelectric properties of the composite. Image 1 • Synthesis of ferroelectric -polymer composites with solution-casting technique. • Structural, microstructural, vibrational and dielectric properties have been studied in detailed. • Ferroelectric properties of the composite correlated to the β-phase. • Percolation theory explained the dielectric properties with the composites. [ABSTRACT FROM AUTHOR]

Single phase lead-free ferroelectric ceramic Na0.5Bi0.5TiO3(NBT) is synthesized using sol-gel method and sintered using microwave sintering technique. The structural, microstructural, and electrical properties are investigated in detail. Rietveld refinement technique is used to analyse XRD pattern. SEM micrograph shows the densely packed micrometre sized grains. Ferroelectric hysteresis loops for unpoled and poled samples confirm its ferroelectric nature. The characteristic ferroelectric properties like remanent polarization and coercive field are found to be 84.8 µC/cm2, 71.8 µC/cm2and 58.8 kV/cm, 58.6 kV/cm respectively for the unpoled and poled samples. The current versus voltage curve of the NBT follow the bulk-limited space-charge conduction mechanism. [ABSTRACT FROM AUTHOR]

The conduction mechanism of polymer nano-composite electrolytes are studied using broadband dielectric spectroscopy over a wide range of frequency and temperature. The polymer nano-composites consisting of polyethylene oxide as polymer host, lithium trifluoromethanesulfonate as salt, and nano-crystalline zirconia as filler are prepared using solution casting method. Formation of polymer salt complex and nano-composites are confirmed from x-ray diffraction studies. The electrical conductivity and relaxation phenomena of the polymer salt complex as well as the composites are studied using broadband dielectric spectroscopy. At room temperature, the dc conductivity of the polymer nano-composites are found higher by two orders of magnitude than that of corresponding polymer salt complex. Temperature dependence of dc conductivity is following Vogel-Tamman-Fulcher trend, suggesting strong coupling between ionic conductivity and segmental relaxation in polymer electrolytes. Relaxation phenomena are studied with dielectric and modulus formalism. Frequency dependent ac conductivity show universal dielectric response and nearly constant loss features at high and low temperature regions respectively. The origin of universal dielectric response and nearly constant loss are analysed and discussed using different approaches. Kramer - Krönig approach suggests the origin of nearly constant loss is due to caged ion dynamics feature. [ABSTRACT FROM AUTHOR]

Preparation and characterization of soy lecithin (SL) and palm oil (PO) based organogels have been reported in this study. The optimization of the composition of the organogels was carried out by varying the proportions of SL, PO and water. Microscopic studies suggested the presence of aqueous phase either as spherical droplets or fluid filled fibers or both, depending on the composition of the organogels. FTIR study indicated strong intermolecular hydrogen bonding among the organogel components. The release of metronidazole (model drug, MZ) suggested diffusion mediated drug release. MZ loaded organogels showed good antimicrobial property againstB. subtilisandE. coli. [ABSTRACT FROM PUBLISHER]

A series of lead-free perovskite solid solutions of (1 − x) Na0.5 Bi0.5 TiO3( NBT)- x BaSnO3( BSN), for 0.0 ≤ x ≤ 0.15 have been synthesized using a high-temperature solid-state reaction route. The phase transition behaviors are studied using dielectric and Raman spectroscopic techniques. The ferroelectric to relaxor phase transition temperature ( TFR) and the temperature corresponding to maximum dielectric permittivity ( Tm) are estimated from the temperature-dependent dielectric data. Dielectric studies show diffuse phase transition around ~335°C in pure NBT and this transition temperature decreases with increase in x. The disappearance of x-dependence of A1 mode frequency at ~134 cm−1 for x ≥ 0.1 is consistent with rhombohedral-orthorhombic transition. In situ temperature dependence Raman spectroscopic studies show disappearance and discontinuous changes in the phonon mode frequencies across rhombohedral ( x < 0.1)/orthorhombic ( x ≥ 0.1) to tetragonal transition. [ABSTRACT FROM AUTHOR]

Polycrystalline nano BiFeO3 powders were synthesized by auto-combustion method using urea as fuel and metal nitrates (Fe(NO3)3·9H2O, Bi(NO3)3·5H2O) as oxidizers. In order to optimize the single-phase synthesis condition of BiFeO3, different fuel to oxidizer ratios have been investigated. The preliminary structural investigation using X-ray diffraction shows the samples were of single phase and crystallize in rhombohedral structure (R3c). The ferroelectric and antiferromagnetic ordering temperatures of BiFeO3 were found to be 832 °C and 364 °C respectively, from differential thermal analysis. The temperature dependent dielectric study shows an anomaly around 215 °C which corresponds to magneto-electric coupling in the material. Field-emission scanning electron micrographs show effect of fuel to oxidizer ratio on grain size evolution. The ferroelectric hysteresis loops for all the samples were measured at a frequency of 100 Hz confirming the ferroelectric nature. An evidence of magneto-electric coupling was also observed at room temperature from magneto-capacitance measurements. [ABSTRACT FROM AUTHOR]

Multiferroic materials have attracted considerable attention as possible candidates for a wide variety of future microelectronic and memory devices, although robust magnetoelectric (ME) coupling between electric and magnetic orders at room temperature still remains difficult to achieve. In order to obtain robust ME coupling at room temperature, we studied the Pb(Fe0.5Nb0.5)O3/Ni0.65Zn0.35Fe2O4/Pb(Fe0.5Nb0.5)O3 (PFN/NZFO/PFN) trilayer structure as a representative FE/FM/FE system. We report the ferroelectric, magnetic and ME properties of PFN/NZFO/PFN trilayer nanoscale heterostructure having dimensions 70/20/70 nm, at room temperature. The presence of only (00l) reflection of PFN and NZFO in the X-ray diffraction (XRD) patterns and electron diffraction patterns in Transmission Electron Microscopy (TEM) confirm the epitaxial growth of multilayer heterostructure. The distribution of the ferroelectric loop area in a wide area has been studied, suggesting that spatial variability of ferroelectric switching behavior is low, and film growth is of high quality. The ferroelectric and magnetic phase transitions of these heterostructures have been found at ~575 K and ~650 K, respectively which are well above room temperature. These nanostructures exhibit low loss tangent, large saturation polarization (Ps ~ 38 µC/cm2) and magnetization (Ms ~ 48 emu/cm3) with strong ME coupling at room temperature revealing them as potential candidates for nanoscale multifunctional and spintronics device applications. [ABSTRACT FROM AUTHOR]