Electric Polarization Properties Research Articles

Experimental and theoretical studies: Impact of Mg-Yb double substitution on structural, dielectric and electrical properties of nanoferrites

This research project was designed to understand the synergistic effect of Mg2+ and Yb3+ ions substitution on structural, dielectric, electrical resistivity and electrical polarization properties of Sr1-xMgxFe4-yYbyMn2O11 (x = 0, 0.1, 0.2, 0.3 and y = 0, 0.02, 0.06, 0.1) R-type hexagonal ferrites prepared via sol–gel auto combustion method. The XRD graphs revealed that the present synthesized material exhibited the single phase. The Rietveld refinement was also carried out to fit XRD patterns which confirmed the single phase for all samples. The SEM micrographs indicate the platelet like structure for the grains. The curve fitting of real and imaginary part of permittivity results was done by using the modified Debye function. The ac conductivity enhanced with frequency. The electrical resistivity, calculated in the voltage range of (-200 V to 0 V) and (0 V to 200 V) was found to vary with Mg-Yb substitution. The P-E loops for each concentration unveiled the loosy behavior.

Electronic structure and multiferroic properties of (Y, Mn)-doped barium hexaferrite compounds

We have systematically studied the crystal and electronic structures and the magnetic and electrical polarization properties of polycrystalline Ba0.95Y0.05Fe12−xMnxO19 (denoted as BaYFe12−xMnxO19) compounds with x = 0–2. The analyzes of X-ray diffraction patterns and Raman scattering spectra indicated their single phase in the M-type hexaferrite structure. With increasing x, the lattice constant a slightly increased while c decreased, which related to the Jahn-Teller effect. Though an increase of x reduced gradually magnetization in a range of 23–32 emu/g, the coercive force increased from 3.3 kOe for x = 0 to about 4 kOe for x = 0.5–2. The study of the electrical polarization properties proved the dependence of the shape of electric hysteresis loops on x and applied electric field. The samples with x = 0 and 0.5 exhibit a weak ferroelectricity with the maximum polarization of ~0.11 μC/cm2 for x = 0, and of ~0.06 μC/cm2 for x = 0.5. Meanwhile, the other samples showed nearly circular hysteresis loops, which are characteristic of conductive materials. Detailed investigations indicated an increase in leakage current when x increased. All of such phenomena are tightly related to the chemical shift of Mn2+ → Mn3+ and the replacement of Mn2+,3+ for Fe3+ in BaYFe12−xMnxO19. These oxidation states and the chemical shift of Mn have been confirmed upon analyzing X-ray absorption spectra.

The separation assessment of small-seeded mixtures of agricultural crops

The paper confirms that the effective separation of small-seeded mixtures of crops can be achieved if we use electrical separation methods that take into account the difference in electrical conductivity and dielectric constant of the components, their ability to receive and give a charge etc. Having examined electrical conductivity and polarization properties of winter oilseed rape and Galium aparine seeds by the method of impedance spectroscopy, it was found out that the frequency dependence of the real part of their complex resistance is of the same type and has a decreasing character. The maximum capacity of winter oilseed rape is 50 % higher than the corresponding capacity of Galium aparine, and the maximum accumulation of charge by seeds is observed in the frequency band for which the real part of the complex resistance takes close values for both Galium aparine and winter oilseed rape. The revealed difference in electrical conductivity and dielectric constant of the studied seeds of winter oilseed rape and Galium aparine causes different charges, which is one of the main conditions for their effective separation in electric separators, which use an electric field of corona discharge as an additional working body.

Crack resistance of bismuth ferrite films obtained on a flexible substrate

Ultrathin BiOx and FeOx layers were obtained by Atomic Layer Deposition (ALD) on the surface of a flexible Kapton substrate (poly (4,4’-oxydiphenylene-pyromellitimide)) at a temperature of 250 °C. The layer thickness was 50 - 100 nm. Surface morphology, electrical polarization, and mechanical properties were investigated by Atomic Force Microscope, Piezoelectric Force Microscopy and Force Modulation Microscopy. Chemical analysis was performed by X-ray Photoelectron Spectroscopy, where the formation of Bi2O3 and Fe2O3 phases, as well as intermediate phases in the Bi-Fe-O system, was observed. With a small increase in the Bi content of the film, the BFO / Kapton structure becomes more crack resistant. Modification of the Kapton surface with bismuth and iron oxides showed that such a composition exhibits multiferroic behavior.

Studies of structural, dielectric and impedance spectroscopy of Ca/Zr modified BiFeO3 ceramics

In this communication, the structural and electrical (dielectric, polarization, impedence, and conductivity) properties of the polycrystalline samples of Ca/Zr modified BiFeO3 samples with chemical formula (Bi1-xCax) (Fe1-xZrx)O3; x = 0.05, 0.1, 0.15, 0.20 were prepared using a solid-state reaction method at 800 °C have been reported. The analysis of room temperature X-ray diffraction data of above-synthesized electro-ceramics confirms the formation of single phase perovskite in rhombohedral phase. The scanning electron microscope photographs provide the micro-structural study of the samples. The existence of ferroelectricity in the materials was studied by the variation of electric polarization with the applied electric field. Many important results have been obtained from the dielectric and impedance studies of the samples at a varying frequency (1 kHz–1000 kHz) and temperature (250C–300 °C). The contribution of both grains and grain boundaries towards the total resistance and capacitance of the four compounds is found from the Nyquist plots. From the conductivity study, the dielectric properties and conductivity of the materials were obtained. The J–E characteristics of the samples provide the Ohmic behavior with slope closer to 1.

Tunable spin textures in polar antiferromagnetic hybrid organic\u2013inorganic perovskites by electric and magnetic fields

The hybrid organic–inorganic perovskites (HOIPs) have attracted much attention for their potential applications as novel optoelectronic devices. Remarkably, the Rashba band splitting, together with specific spin orientations in k-space (i.e., spin texture), has been found to be relevant for the optoelectronic performances. In this work, by using first-principles calculations and symmetry analysis, we study the electric polarization, magnetism, and spin texture properties of the antiferromagnetic (AFM) ferroelectric HOIP TMCM-MnCl3 (TMCM = (CH3)3NCH2Cl+, trimethylchloromethyl ammonium). This recently synthesized compound is a prototype of order–disorder and displacement-type ferroelectric with a large piezoelectric response, high ferroelectric transition temperature, and excellent photoluminescence properties as reported by You (Science 357:306, 2017). The most interesting result is that the inversion symmetry breaking coupled to the spin–orbit coupling gives rise to a Rashba-like band splitting and a related robust persistent spin texture (PST) and/or typical spiral spin texture, which can be manipulated by tuning the ferroelectric or, surprisingly, also by the AFM order parameter. The tunability of spin texture upon switching of AFM order parameter is largely unexplored and our findings not only provide a platform to understand the physics of AFM spin texture but also support the AFM HOIP ferroelectrics as a promising class of optoelectronic materials.

Ferroelectricity in CaBaCo4O7 by light non magnetic Zn doping

CaBaCo4O7 (CBCO) cobaltite shows a giant spin driven pyroelectric polarization below its ferrimagnetic transition temperature at 64 K. In the present study, we have investigated the structural, magnetic and electric polarization properties of light nonmagnetic Zn doped polycrystalline CaBaCo3.97Zn0.03O7 (CBCZO) cobaltite. Neutron powder diffraction studies on the CBCZO show that the Zn occupies the Co2 sites which lowers the strength of the magnetic interactions between the bitetrahedral cobalt c-axis chains. Further, we show that these chains act as magnetic clusters and causes the switching of the electric polarization. This study specifies that the ferrimagnetic–pyroelectric ground state of CBCO is very sensitive to the light non-magnetic doping and the results can be used to further understand the pyroelectric polarization switching properties of CBCO.

La3+-substituted β-ferrite: Investigation of structural, dielectric, FTIR and electrical polarization properties

Abstract This research article reports the exploration of structural, dielectric, optical and electrical polarization properties of β-type hexagonal ferrite KLaxFe11-xO17 upon the substitution of rare earth element La3+ with compositions (x = 0, 0.02, 0.06 and 0.1). The samples were synthesized by adopting the sol-gel auto-combustion technique and the sintering temperature was 950 °C. The XRD patterns revealed the single hexagonal phase for all the samples. The lattice parameters a (A), c (A), crystallite size (nm), X-ray density (g/cm3) and unit cell volume V (A) 3 changed with La3+ substitution. The crystallite size was found to be varied in the range from 24 to 27 nm for all samples as calculated from Scherer formula. Fourier transform infrared spectroscopy (FTIR) spectra also confirmed the single phase for the synthesized samples. The dielectric constant exhibited the higher values than the pure sample with substitution. The dielectric constant results were fitted with the Debye function which indicated the participation of more than one ion in the increment of dielectric constant. The real (M′) and imaginary (M″) part of complex modulus graphs delineated the peaks shifting towards high and low frequency region which confirmed the occurrence of relaxation phenomenon in material. The polarization verses electric field loops corroborated the decrease in saturation and remnant polarization with La3+ contents. The P-E loops also showed the lossy behavior and the increment in lossy behavior with substitution pointed out the increase in resistivity of the samples. From aforementioned evidences, it is confirmed that the present synthesized beta ferrites are useful in the fabrication of humidity sensors and to reduce the eddy current losses.

High‐performance poly(vinylidene fluoride)‐polyamide 11/lithium niobate nanocomposites for the applications in air filtration

ABSTRACTTo overcome the fiber‐spinning problem of poly(vinylidene fluoride) (PVDF) because of its high melt viscosity and rapid crystallization, polyamide 11 (PA11) with excellent melt spinning capability and good electret properties is incorporated to prepare blends by melt mixing. Their crystal structure, morphology, electrical polarization properties, and melt spinning performance are systematically characterized by various techniques. It is found that the incorporation of PA11 reduces the crystallinity of PVDF, increases its thermally stimulated discharge current, and reduces its viscosity. Therefore, the blends show much better melt spinning capability. For such blends, the addition of outstanding inorganic electret materials, lithium niobate (LiNbO3, LN) nanoparticles is found to further improve the materials’ electret properties. Such a strategy is proved to be successful in melt spinning PVDF electrets into fine fibers, which is beneficial to their applications in air filtration and other related fields. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48957.

Strain-induced structural phase transition, electric polarization and unusual electric properties in photovoltaic materials CsMI3 (M = Pb, Sn).

The structural phase transition, ferroelectric polarization, and electric properties have been investigated for photovoltaic films CsMI3 (M = Pb, Sn) epitaxially grown along (001) direction based on the density functional theory. The calculated results indicate that the phase diagrams of two epitaxial CsPbI3 and CsSnI3 films are almost identical, except critical transition strains varying slightly. The epitaxial tensile strains induce two ferroelectric phases Pmc21, and Pmn21, while the compressive strains drive two paraelectric phases P212121, P21212. The larger compressive strain enhances the ferroelectric instability in these two films, eventually rendering them another ferroelectric state Pc. Whether CsPbI3 or CsSnI3, the total polarization of Pmn21 phase comes from the main contribution of B-position cations (Pb or Sn), whereas, for Pmc21 phase, the main contributor is the I ion. Moreover, the epitaxial strain effects on antiferrodistortive vector, polarization and band gap of CsMI3 (M = Pb, Sn) are further discussed. Unusual electronic properties under epitaxial strains are also revealed and interpreted.

Tunable properties of rare earth elements (Ce, Dy, Yb, La and Pr) substituted R-type hexagonal ferrites

A series of rare earth elements (RE = Ce, Dy, Yb, La and Pr) substituted Sr0.9RE0.1Mn2Fe4O11 R-type hexagonal ferrites has been prepared by using the Sol–gel technique. The effect of RE substitution on its structural, electric polarization, dielectric and microwave absorption properties was studied. XRD patterns showed that all the prepared samples possess R-type hexagonal structure. The lattice parameters and unit cell volume varied with the substitution of RE contents. The average crystallite size, measured by Scherer formula, varied in the range of 6–15 nm for all samples. These results make this material suitable for being used in multilayer chip inductors (MLCI’s). The dielectric constant was found to decrease at high frequencies. This behavior has been explained on the basis of Maxwell–Wagner’s and Koop’s theory. An increase in AC conductivity was observed with increase in frequency. The decrease in lossy behavior with RE substitution in pure sample indicated the increase in the resistive nature of samples as observed from the electric polarization analysis. The Yb substituted sample exhibited highest value of microwave absorption − 40.5 dB at 11.4 GHz frequency among all the substituted samples.

Structural, magnetic and electric-polarization properties of geometrically frustrated YBaCo4O7and DyBaCo4O7cobaltites

In the RBaCo4O7 (R = Ca, Y and rare earth) cobaltite family, only CaBaCo4O7 shows 3D long-range ferrimagnetic and spin-driven electric-polarization properties. In the present study, we have investigated the structural, magnetic and electric polarization properties in YBaCo4O7 and DyBaCo4O7 members of this family and the obtained results are compared with the CaBaCo4O7. The compound YBaCo4O7 showed a series of magnetic transitions in agreement with the reported literature, additionally, a cluster glass behavior below 5 K is observed. Powder neutron diffraction studies on DyBaCo4O7 cobaltite showed an orthorhombic Pbn21 symmetry and signature of short-range 120° magnetic correlations of kagome layer and a spin glass behavior below 65 K. Dielectric measurements on both the samples showed strong frequency dispersion at high-temperature and frequency-independent behavior at low temperature without dielectric anomaly. Pyroelectric current measurement has showed a broad peak around 50 K in both the samples; however, a careful analysis relates the peak to thermally stimulated depolarization current. This study signifies that the giant structural distortions and cobalt charge ordering at the kagome layer are the key factors to drive both long-range magnetic ordering and spin-driven electric polarization in this cobaltite family.

A reduced symmetric 2D photonic crystal cavity with wavelength tunability

In this paper, we propose a microcavity supported by a designed photonic crystal structure that provides both tunability of cavity modes and the cavity’s quality factor. A low symmetric defect region provides a trigger effect for the frequency shifting by means of rotational manipulation of small symmetry elements. Deviation of the effective filling ratio as a result of rotational modification within the defect region results in the emanation of cavity modes at different frequencies. Here, we numerically demonstrate the frequency shifting for each obtained mode with respect to the defect region architecture. In addition to wavelength tunability, quality factor, mode volume, and Purcell factors are analyzed for the slightly modified structures. Besides, electric field distributions and polarization properties of each mode that emerge at distinct frequencies have been studied at adjusted frequency modes which are observed for all rotational modification scenarios as . After the investigations in 2D of silicon material (), 3D simulations are performed and the collected data is used for the height approximation of 3D structures to approach the results consistent with 2D ones, thus the cross-checking of the quality factor acquired from the 2D simulation can be executed by comparison with 3D. Moreover, 2D and 3D simulations of alumina material () in terms of mode analysis and quality factor have been repeated considering the microwave experiments. Therefore, experimental analysis is compared with the numerical results and good agreement between the two is found.

Functional magnetoelectric composites with magnetostrictive microwires

This paper discusses the electric polarization properties of ferromagnetic microwires at microwave frequencies. At the vicinity of the antenna resonance, a strong magnetic control of the wire polarization is possible owing to the magnetoimpedance (MI) effect. In order to realize efficient tunable properties, magnetic microwires of Co-rich compositions in amorphous state are considered. The absence of the crystalline structure is an important condition to establish well-defined magnetic anisotropies of small magnitudes, which results in the magnetization processes sensitive to the external parameters such as a magnetic field and a mechanical stress. Tunable soft magnetic properties of amorphous microwires are responsible for the MI effect, which can be observed at high frequencies (1–10 GHz). Here we demonstrate that the electric polarization of a microwire depends on its impedance and, hence, can be modulated changing the wire magnetization state in response to the application of a magnetic field and a mechanical stress. The polarization problem is treated theoretically by solving the scattering problem from a cylindrical ferromagnetic wire with the impedance boundary conditions. The modelling results agree well with the available experimental data.

Direct study of the electrical properties of PC12 cells and hippocampal neurons by EFM and KPFM.

Electrical related properties play important roles in biological structures and functions. Herein, the capacitance gradient and local contact potential difference (CPD) of cell bodies and processes of PC12 cells (representative cells of the sympathetic nervous system), hippocampal neurons (representative cells of the central nervous system) and spines were investigated by Electrostatic Force Microscopy (EFM) and Kelvin Probe Force Microscopy (KPFM) at high lateral spatial resolution directly. The results demonstrate that the capacitance gradients of cell bodies, processes and spines of PC12 cells and hippocampal neurons are very close (in the range of 19–23 zF nm−1) and fit well with the theoretical calculation results (21.7 zF nm−1). This indicates that the differences of nerve signal activities and functions of the sympathetic and central nervous systems are not related to the electric polarization properties. The CPD of cell bodies and processes of PC12 cells is smaller than that of hippocampal neurons. The CPD of spines is much more negative than that of the cell bodies and processes. These results reveal that the surface potential is closely related to the neural signal transduction functions, and spines play vital roles in neural signal transmission. This work indicates the similarity (capacitance gradient) and differences (surface potential) of the electrical properties between the sympathetic and central nervous systems for the first time. The methods and results of this work are useful in the further study of the electrical properties in cellular activities and physiological processes.

Electrical conductivity and induced polarization investigations at Krafla volcano, Iceland

Electrical conductivity and polarization properties of 6 samples from Krafla volcano (Iceland) were measured in the frequency range 1 mHz–45 kHz and compared to the data obtained on various basaltic rock samples from Hawaii. The results indicate that for altered samples, the surface conductivity, normalized chargeability, and quadrature conductivity of the core samples scales linearly with the cation exchange capacity, taken as a proxy of the alteration facies. The surface conductivity of fresh samples is also controlled by the cation exchange capacity but their normalized chargeability is influenced by the presence of magnetite, especially for unaltered samples. The temperature dependence of quadrature conductivity and normalized chargeability can be modeled with an Arrhenius equation with an activation energy of 16–19 kJ mol−1. The experimental results agree with a model in which the polarization of the metallic and non-metallic grains are both considered in a unified framework. These results are used to interpret two 3D induced polarization surveys performed in the South and East parts of Krafla volcano using two 1.3 km-long cables with 32 electrodes each. The electrical conductivity is in the range 0.3 (clay cap) to 5 × 10−5 S m−1 (unaltered rock) while the normalized chargeability is typically comprised between 10−2 (clay cap) and 10−5 S m−1 (unaltered rock). Induced polarization is used to image porosity and the cation exchange capacity. A long 5.6 km electrical conductivity profile was also performed connecting the two 3D sites and crossing a rhyolitic obsidian ridge called Hrafntinnuhryggur. Hrafntinnuhryggur is characterized by very low conductivity values on the order of 10−4 S m−1. The long conductivity profile shows the position of the inner and outer caldera rims and the feeder dike of Hrafntinnuhryggur. A self-potential survey performed along this long profile shows no shallow active geothermal features in this area, as expected from the low permeability of the clay cap.

Investigation of structural, electrical, electrical polarization and dielectric properties of CTAB assisted Ni2+ substituted R-type nano-hexaferrites

This paper reports the divalent Ni2+ transition element substituted R-type hexagonal ferrites Sr1-xMn2NixFe4O11 with composition (x = 0, 0.1, 0.2, 0.3) synthesized by sol-gel auto combustion technique. The XRD patterns for all the samples show single phase characteristics. The XRD data was used to calculate the lattice constant a (Å), c (Å), unit cell volume V (Å)3, crystallite size S(nm) and dislocation density D (1/S2). The lattice parameters decreased as the concentration is increased. The range of crystallite size was 11 nm-13 nm. In high density recording media, this small size is proper to obtain the appropriate signal to noise ratio. The observed room temperature (RT) DC electrical resistivity decreased as Ni+2 substitution increased. The conductivity in voltage range of −200 to 200 has been increased. The trend of dielectric constants and dielectric loss factor enhanced with Ni substitution which was due to surface charge polarization. AC conductivity has been enhanced with frequency. In present synthesized material, the conduction process of the material is demonstrated by Cole-Cole graphs which show one semi-circle that influence the grain boundaries. As the Ni+2 concentration is increased the polarization also increased. The increase in dielectric parameters of the synthesized samples with substituents suggests their importance for high frequency applications.

Electric polarization properties of BaTiO3-BiFeO3 as nanomultiferroic material produced by sol-gel method

The nanomultiferroic material which is synthesized in this research used sol-gel method. The research used weight ratio of BaTiO3: BiFeO3 of 2: 1. Gel formed after heating at 80-90°C was calcined at 350°C for 4 hours and then sintered at 700,750 and 800°C for 2, 4 and 6 hours respectively. Powder produced after sintering was characterized by X-Ray Diffraction (XRD) test using XRD Phillips PW 1835 type, 20°-100° diffraction angle and CuKα, electric polarization properties test and particle size measurement using Particle Size Analyzer of Beckman Coulter DelsaTM Nano instrument. From the characterization results, it is obtained that the dominant phase is Barium Bismuth Iron (III) Oxide (BaBiFe2O5). Electrical polarization properties such as remanent, coersivity and saturation reach maximum value at sinter temperature of 750° C and sinter time of 6 hours. This result is supported by the smallest particle size of powder (54-57 nm) and also supported by the largest number of dominant phase (98.79%) at same condition.

Fabrication of poly(o-anisidine) coated silica core–shell microspheres and their electrorheological response

In this work, silica/poly(o-anisidine) (POA) core–shell structured microspheres were synthesized by coating the silica core surface with POA with a help of a chemical grafting agent, N-[(3-trimethoxylsilyl)-propyl] aniline. The synthesized silica microspheres were then applied as a polymer/inorganic composite particle-based electrorheological (ER) fluid. The morphology of the silica/POA microspheres was examined by using both transmission electron microscopy and scanning electron microscopy, while their thermal properties and chemical structure were checked by thermogravimetric analysis and Fourier-transform infrared spectroscopy, respectively. The ER properties of the silica/POA particle-based ER fluid were examined by using a Couette-type rotational rheometer equipped with a high-voltage power supplier and analyzed by the Bingham model and modified Mason number. In order to obtain additional information about the electrical polarization properties, the dielectric spectra were measured by an LCR meter and fitted by using the Cole–Cole equation. Furthermore, suspension stability of the ER fluid was tested using Turbiscan.

Effects of Ga doping on the electric and magnetic properties of DyMn1−xGaxO3

Ga3+ for Mn3+ substitution in multiferroic DyMn1−xGaxO3(x = 0, 0.02, 0.05, 0.1, 0.2, 0.3 and 0.4) has been performed to study the change on Mn3+ ordering, which also influences on the ordering of Dy3+. The samples are pure and their dielectric constant, electric polarization and magnetic properties have been investigated. When the content of Ga3+ increases above 0.1, multiferroic properties completely disappear. These results indicate that Ga3+ for Mn3+ substitution in DyMnO3 bulk can reduce the exchange interactions of JMn−Mn, JDy−Mn and the bond angle of Mn-O-Mn, while the electric polarization is observed to decrease rapidly, even for small Ga doping, and the anomaly at low T in P(T) associated with the Dy ordering is no longer observed for x = 0.05.