Low Coercive Field Research Articles

Doxorubicin Loaded Thermosensitive Magneto-Liposomes Obtained by a Gel Hydration Technique: Characterization and In Vitro Magneto-Chemotherapeutic Effect Assessment.

The combination of magnetic hyperthermia with chemotherapy is considered a promising strategy in cancer therapy due to the synergy between the high temperatures and the chemotherapeutic effects, which can be further developed for targeted and remote-controlled drug release. In this paper we report a simple, rapid, and reproducible method for the preparation of thermosensitive magnetoliposomes (TsMLs) loaded with doxorubicin (DOX), consisting of a lipidic gel formation from a previously obtained water-in-oil microemulsion with fine aqueous droplets containing magnetic nanoparticles (MNPs) dispersed in an organic solution of thermosensitive lipids (transition temperature of ~43 °C), followed by the gel hydration with an aqueous solution of DOX. The obtained thermosensitive magnetoliposomes (TsMLs) were around 300 nm in diameter and exhibited 40% DOX incorporation efficiency. The most suitable MNPs to incorporate into the liposomal aqueous lumen were Zn ferrites, with a very low coercive field at 300 K (7 kA/m) close to the superparamagnetic regime, exhibiting a maximum absorption rate (SAR) of 1130 W/gFe when dispersed in water and 635 W/gFe when confined inside TsMLs. No toxicity of Zn ferrite MNPs or of TsMLs was noticed against the A459 cancer cell line after 48 h incubation over the tested concentration range. The passive release of DOX from the TsMLs after 48h incubation induced a toxicity starting with a dosage level of 62.5 ug/cm2. Below this threshold, the subsequent exposure to an alternating magnetic field (20-30 kA/m, 355 kHz) for 30 min drastically reduced the viability of the A459 cells due to the release of incorporated DOX. Our results strongly suggest that TsMLs represent a viable strategy for anticancer therapies using the magnetic field-controlled release of DOX.

Synthesis of Superhydrophobic Barium Hexaferrite Coatings with Low Magnetic Hardness.

Using the multifunctional material barium hexaferrite as an example, the prospects for treatment at a quasi-equilibrium low temperature in an open atmosphere to form superhydrophobic magnetic coatings with pronounced crystalline and magnetic anisotropy have been demonstrated for the first time. The relationship between plasma treatment conditions, structural-phase composition, morphology, and superhydrophobic properties of (0001) films of barium hexaferrite BaFe12O19 on C-sapphire is studied. X-ray photoelectron spectroscopy (XPS), X-ray diffractometry (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), as well as magnetometry and moisture resistance analysis, were used as research methods. During plasma treatment with a mass-average temperature of 8-10 kK, intense evaporation and surface melting were observed, and texturing of the deposit along (0001) is found. When the treatment temperature was reduced to 4-5 kK, the evaporation of the material was minimized and magnetic and crystal anisotropy increased. However, the increase in the size of crystallites was accompanied by the transition of oxygen atoms from lattice nodes to interstitial positions. All samples exhibited low coercive fields below 500 Oe, associated with the frustration of the magnetic subsystem. Features of growth of materials with a wurtzite structure were used to form a superhydrophobic coating of barium hexaferrite. Plasma treatment regimes for obtaining self-cleaning coatings are proposed. The use of magnetically hard barium hexaferrite to radically change the properties of a coating is demonstrated herein as an example.

Significantly enhanced hybrid improper ferroelectricity of Ca3Ti2O7 ceramics by the oxygen vacancy engineering

Ca3Ti2O7 materials with hybrid improper ferroelectricity call tremendous interest due to their great potential in designing novel room-temperature single-phase multiferroics with a strong magnetoelectric coupling effect. However, achieving Ca3Ti2O7-based ceramics with superior room-temperature ferroelectricity remains a crucial challenge. Herein, Ca3Ti2O7 ceramics were prepared by a tartaric acid sol–gel method and sintered in air and oxygen atmospheres, respectively. It was found that the long-time high-temperature sintering in air could lead to the formation of CaTiO3/Ca3Ti2O7/CaTiO3 sandwich structure, and oxygen-enriched sintering could effectively avoid the formation of CaTiO3 phase on the surface. The superior hybrid improper ferroelectricity is attained in Ca3Ti2O7 ceramics sintered in oxygen atmosphere with a higher remnant polarization (3.63 μC/cm2) and lower coercive electric field (72.6 kV/cm) obtained by positive-up and negative-down method, which is better than the ceramic sample sintered in air. The significantly better ferroelectricity is benefited from the synergistic effects of its larger distortion of oxygen octahedron, larger grain size, and lower oxygen vacancy concentration. Due to its low leakage current density, Ca3Ti2O7 ceramics sintered in oxygen atmosphere exhibit the remanent polarization as high as 7.40 μC/cm2 under the conditions of 1 Hz and 200 kV/cm obtained by dynamic hysteresis measurement mode. Furthermore, there are obvious stripe ferroelectric domains, which provide direct evidence for the excellent hybrid improper ferroelectricity of Ca3Ti2O7 ceramics. These findings demonstrate that the oxygen vacancy engineering is an effective strategy to improve hybrid improper ferroelectricity of Ca3Ti2O7 materials.

Development of energy harvesting and ferroelectric characteristic of thulium doped ZnO via graphene addition

Wet chemical co-precipitation and hydrothermal techniques were used to synthesize Tm-doped GO/ZnO (1:7) nanocomposites. Carbon concentration was found to be different in the prepared Tm-doped GO/ZnO powders. Both thulium doping and the addition of graphene oxide have affected dielectric, ferroelectric and piezoelectric properties of ZnO. The largest value of energy harvesting performance, namely (95 V, 2.40 μAcm−2), was obtained by the piezoelectric nanogenerator of Tm-doped GO/ZnO nanocomposite synthesized by hydrothermal method. The highest remnant polarization (Pr) and the lowest coercive field (Ec) namely (13.15 μC/cm2 and 4.25 kV/cm) were achieved by Tm-doped GO/ZnO nanocomposite synthesized by co-precipitation method. The achievements of present work make Tm-doped GO/ZnO hybrids promising candidates for designing self-powered sensors, energy harvesters and broad-temperature ferroelectric based memory devices.

Role of phonon mode in the enhancement of ferroelectric polarization in a perovskite-based eco-friendly functional material

We report here the role of component freezing of three-dimensional polar () phonon mode corresponding to the center of cubic Brillouin zone in tuning the structure-property correlations of a scientifically enriched and technologically important barium-titanate–based eco-friendly functional material (Ba0.92Ca0.08)(Zr0.05Ti0.95−x Sn x )O3; BCZTSnx synthesized via solid-state reaction method. The combined X-ray diffraction, Raman spectroscopic analysis, and temperature-dependent dielectric studies have revealed the presence of several crystallographic phase transitions with coexisting phases, viz., , as a function of Sn(x) content. These crystallographic phases, viz., P4mm, Amm2, and R3m results due to freezing of the component(s) of phonon mode (belonging to space group), with the respective order parameter directions (0,0,a), (a,a,0), and (a,a,a) leading to ferroelectric polarization along , and directions, respectively. The ceramic composition corresponding to exhibits a significant reduction in the coercive field (E c ) and an enhancement in ferroelectric polarization (P r ) in comparison to , inferred from PE loop measurements. The enhancement in ferroelectric polarization at has been attributed to the inter-ferroelectric three-phase coexistence around this composition and significantly enhanced amplitudes of ferroelectric phonon modes corresponding to orthorhombic and rhombohedral phases, calculated using the symmetry mode analysis technique. The existence of a high ferroelectric polarization and low coercive field may lead to composition as an eco-friendly candidate for ferroelectric memory devices.

Rare-earth ferrobismuthites: ferromagnetic ceramic semiconductors with applicability in spintronic devices

We report here the synthesis process of the perovskite-like complex material Bi0.5R0.5FeO3 (R=Eu, Sm, Dy) using the ceramic method, as well as its structural, optical, magnetic, and electrical characterizations. Refined X-ray diffraction data revealed that this material crystallizes in an orthorhombic structure (space group Pnma number 62). The band gap value in the optical response shown in the diffuse reflectance spectroscopy curve was typical of semiconductor materials. The magnetization exhibited a very low coercive field hysteretic behavior, which is characteristic of weak ferromagnetism, for all temperatures examined below 300 K and the various magnetic fields applied. The real and complex electric permittivity curves showed the occurrence of dielectric relaxation processes at 113 K in agreement with reports of pyroelectric and thermo-stimulated currents as a function of temperature revealing the appearance of ferroelectric polarization below 113 K with possible magnetoelectric coupling. On the other hand, we made a theoretical study of the electronic structure with and without the inclusion of a Berry distortional phase and ab-initio calculations following the density functional theory formalism and the pseudopotential plane wave method. In this formalism, the exchange and correlation mechanisms are described by the generalized gradient approach (GGA + U) considering spin polarization. The Berry phase analysis suggested the occurrence of ferroelectricity at temperatures below 113 K consistent with the experimental analysis evidencing a biferroic behavior at low temperatures given that the distortional phase introduces hybridizations between the 3d-Fe and 2p-O states favoring the appearance of Dzyaloshinskii-Moriya interactions, which, in turn, facilitate the appearance of ferroelectricity coexisting with a weak ferromagnetism. The thermodynamic properties in the presence or absence of the Berry phase by means of the Debye quasiharmonic model revealed the appearance of a ferroelectric transition at 113 K, which corroborates their magnetoelectric nature at low temperatures. The ferromagnetic semiconducting character found at room temperature enhances this material for applications in spintronics technology.

Micromagnetic Modeling of a Magnetically Unstable Zone and Its Geological Significances

AbstractRecent micromagnetic simulations have found that particles in the transitional zone between the single domain (SD) and single vortex (SV) zone are prone to thermal and external magnetic field instabilities that could adversely affect the accuracy of interpretations of paleomagnetic recordings. In this study, we attempt to evaluate the internal magnetization characteristics of these magnetically unstable (MU) particles and the influence on paleomagnetic observations by simulating the magnetic behavior of 68–104 nm truncated octahedral magnetite particles using the MERRILL modeling software. We found that: (a) The size region of the “MU zone” for grains of truncated octahedron shape is different from cubic octahedrons and spheres, indicating that the zone may be controlled by the geometry and shape of particles; (b) The MU zone has a range of 79–97 nm region, which is dominated by a hard‐axis aligned single vortex (HSV); and (c) MU particles are unstable as a function of temperature and have low coercive fields. Finally, the numerical fitting of hysteresis parameters for experimental data suggests that the influence of such MU particles in samples should not be ignored, especially for samples with fine‐grained magnetic minerals as the primary magnetic recording carriers. This research has extended our understanding of the behavior of the “MU zone” and its significance on paleomagnetic records.

Critical Importance of Nonuniform Polarization and Fringe Field Effects for Scaled Ferroelectric FinFET Memory

The ferroelectric field-effect transistor (FEFET) is an emerging nonvolatile memory technology that can offer ultra-scalability, fast operation, and reduced power consumption. However, a limited understanding of FEFET physics poses challenges for optimum device design. In this article, we provide physical insights into the operation of FinFET-based FEFETs (FEFinFETs) using a phase-field framework built on time-dependent Landau–Ginzburg (TDGL) thermodynamic theory. We exploit the source–drain fringing field to stabilize a monodomain configuration in the OFF state of short channel FEFinFETs. Based on recent experiments, we first analyze the switching dynamics of FEFinFETs with low remnant polarization ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${P}_{r}$ </tex-math></inline-formula> ) and high coercive field ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{c}$ </tex-math></inline-formula> ) hafnium zirconium oxide (HZO) FE. We find that the switching in these FEFinFETs occurs via domain nucleation and growth from the gate metal edges at the source–drain spacers. We also show that a non-zero drain bias can be used for dynamically modulating the memory window (MW) of FEFinFET to lower its power consumption. Furthermore, we find the spacer permittivity to be a crucial design parameter to control the MW and show that a lower spacer permittivity can significantly increase the MW. Finally, we show that the commonly held idea that a large <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${P}_{r}$ </tex-math></inline-formula> leads to a large MW is not always valid. For a large <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${P}_{r}$ </tex-math></inline-formula> , the formation of multiple domains in the FE layer can lead to a significant reduction in the MW. In addition, these devices can suffer from low write endurance due to exposure of the interfacial oxide layer to high electric fields.

Magnetization controlled by crystallization in soft magnetic Fe-Si-B-P-Cu alloys.

Soft magnetic materials have low coercive fields and high permeability. Recently, nanocrystalline alloys obtained using annealing amorphous alloys have attracted much interest since nanocrystalline alloys with small grain sizes of tens of nanometers exhibit low coercive fields comparable to that of amorphous alloys. Since nanocrystalline soft magnetic materials attain remarkable soft magnetic properties by controlling the grain size, the crystal grains' microstructure has a substantial influence on the soft magnetic properties. In this research, we examined the magnetic properties of Fe-Si-B-P-Cu nanocrystalline soft magnetic alloys obtained by annealing amorphous alloys. During crystallization, the observation findings reveal the correlation between the generated microstructures and soft magnetic properties.

Tetrahydroxyquinone: A Suitable Coating for Ferrofluids Used in Magnetic Hyperthermia

In this work, tetrahydroxyquinone (THQ) was used for the first time to coat iron oxide nanoparticles (IONPs) and to carry out in vitro experiments in magnetic hyperthermia. Synthesis by co-precipitation resulted in spherical IONPs with a core diameter of 13 ± 3 nm and covered by a 0.5 nm thick coat of THQ, which provided them with a reasonably good zeta potential of ζ = −28 ± 2 mV at pH = 7.3, and thus colloidal stability. The magnetic properties of the THQ-coated IONPs are promising: the low coercive field of Hc = 7 Oe, the high magnetic saturation of Ms = 70.5 emu/g and the low blocking temperature of Tb = 273 K indicate superparamagnetic characteristics at room temperature. Additionally, a high specific absorption rate SAR = 135 W/g (at 300 Oe and 530 kHz) was determined. Cell biological experiments using the human cell line HT-29 evidenced negligible cytotoxicity up to 2 mg/mL. Magnetic hyperthermia (MHT) assays demonstrated fast and reliable heating and reduced the metabolic activity of the cells to 42% upon reaching 42 °C within 15 min. The production of ROS by THQ-coated IONPs could not be detected, which may indicate a reduction in the undesired side effects caused by oxidative stress. Considering these good physicochemical and cell biological properties, this ferrofluid is a promising candidate for the initiation of in vivo experiments for cancer treatment by MHT in murine models.

Tapioca starch in the sol-gel synthesis of cobalt ferrites with divalent cation substitutions

An aqueous solution of tapioca starch was successfully used as a chelating agent in the sol-gel synthesis of Co0.7Me0.3Fe2O4, where Me denotes Co, Mn, Cu, Ni, or Zn. The hysteresis loops of all sintered ferrites revealed ferrimagnetic properties. The saturation magnetization was reduced in Co0.7Cu0.3Fe2O4 and Co0.7Ni0.3Fe2O4 because of the ion substitutions with smaller magnetic moments. Interestingly, Co0.7Cu0.3Fe2O4 exhibited the highest saturation magnetization and the lowest coercive field. This result demonstrates the value addition of local agricultural products in controlling nanoparticle formation during sol-gel synthesis.

Effect of Crystal Structure and Phase on the Dielectric, Ferroelectric, and Piezoelectric Properties of Ca2+- and Zr4+-Substituted Barium Titanate

Barium titanate (BaTiO3) and its associate ternary metal oxide systems constitute versatile materials with immense potential for various technological applications in electronics and optoelectronics. Herein, we report on the synthesis and property optimization of lead-free ceramic samples, namely BaTiO3 (BT), BaZr0.2Ti0.8O3 (BZT), Ba0.7Ca0.3TiO3 (BCT), and BaZr0.2Ti0.8O3–0.5 Ba0.7Ca0.3TiO3 (BZT–BCT) composites. All of these materials were synthesized by the standard solid-state chemical reaction method, where tuning the composition and the crystal structure yields materials suitable for multifaceted applications related to capacitors, memory storage, and high-energy switching and transducers. Structural studies carried out using X-ray diffraction and Raman spectroscopy confirm the tetragonal phase for BT, BZT, and BZT–BCT samples, whereas BCT is a biphasic crystal system, which contains a small amount of the CaTiO3 phase. Scanning electron microscopy characterization of the surface morphology indicates the granular-dense microstructures of all of the samples. Energy dispersive spectroscopy confirms the high degree of purity and chemical homogeneity of the synthesized samples in addition to a well-maintained composition. Density measurements using Archimedes principles show that all of the samples have densities above 4.96 g/cm3. All of these materials exhibit typical polarization–electric field (P–E) hysteresis and field-induced strain butterfly (S–E) loops, which confirm their ferroelectric and piezoelectric nature. The frequency response of the dielectric constant shows a maximum dielectric constant of 2441 for pure BT and it decreases for higher frequencies, above 0.1 MHz. The dielectric properties of BT imply significant prospects for its future capacitor applications. Ferroelectric measurements, which are established by measuring the P–E hysteresis loop at 300 K, show that the BCT samples exhibit a 0.50 squareness ratio. The detailed analyses indicate that BCT is a candidate material for permanent memory storage device (FeRAM) applications, whereas BZT is good for switching applications. Furthermore, a moderately higher remnant polarization (Pr = 10.81 μC/cm2) is obtained for BT and a lower coercive field (Ec = 0.78 kV/cm) is obtained for the BZT sample. Also, piezoelectric coefficient and strain measurements show that BT has a piezoelectric coefficient of 183 ± 1 pC/N and a converse piezoelectric coefficient of 365.7 ± 2 pm/V, which are the highest values. The Q-factor for the BZT–BCT composite was observed to be 4.16 × 10–4 (cm2/μC)2, which is maximum, implying that BZT–BCT is suitable for energy conversion transducer applications. In this work, we comprehensively elucidate and discuss the properties and potential applications of BT and its associated ternary metal oxide systems.

Effect of an oscillating magnetic field in polymeric columns with magnetic nanoparticles

Magnetite magnetic nanoparticles (MNP) exhibit superparamagnetic behavior, which gives them important properties such as low coercive field, easy superficial modification and acceptable magnetization levels. This makes them useful in separation techniques. However, few studies have experimented with the interactions of MNP with magnetic fields. Therefore, the aim of this research was to study the influence of an oscillating magnetic field (OMF) on polymeric monolithic columns with vinylated magnetic nanoparticles (VMNP) for capillary liquid chromatography (cLC). For this purpose, MNP were synthesized by coprecipitation of iron salts. The preparation of polymeric monolithic columns was performed by copolymerization and aggregation of VMNP. Taking advantage of the magnetic properties of MNP, the influence of parameters such as resonance frequency, intensity and exposure time of a OMF applied to the synthesized columns was studied. As a result, a better separation of a sample according to the measured parameters was obtained, so that a column resolution (Rs) of 1.35 was achieved. The morphological properties of the columns were evaluated by scanning electron microscopy (SEM). The results of the chromatographic properties revealed that the best separation of the alkylbenzenes sample occurs under conditions of 5.5 kHz and 10 min of exposure in the OMF. This study constitutes a first application in chromatographic separation techniques for future research in nanotechnology.

An innovative procedure for synthesizing Al70M20(Fe, Co)Cr10 amorphous nanoparticles by arc discharge method and investigation of their magnetic, hardness, and corrosion resistance properties

Al70Fe20Cr10 and Al70Co20Cr10 amorphous nanoparticles were prepared by plasma arc discharge process under arc current of 50 A and 1 atm. pressure in liquid nitrogen medium. XRD patterns of the as-prepared powders exhibit amorphous nature. According to TEM images, the Al70Fe20Cr10 and Al70Co20Cr10 amorphous nanoparticles have a spherical shape with a mean size of 27 and 35 nm, respectively. Static magnetic measurements using a vibrating sample magnetometer (VSM) indicate that the Al70Co20Cr10 amorphous alloy has a higher saturation magnetization of 9.3 emu/g and a lower coercive field of 14 Oe compared with 3.8 emu/g and 45 Oe for the Al70Fe20Cr10 amorphous alloy. In contrast, the Al70Fe20Cr10 amorphous alloy has a higher hardness and shows approximately 20 times more corrosion resistance than the Al70Co20Cr10 amorphous alloy.

Lower ferroelectric coercive field of ScGaN with equivalent remanent polarization as ScAlN

The ferroelectricity of wurtzite, Sc x Ga1−x N (x = 0.35–0.44), was demonstrated in a metal–ferroelectric–metal capacitor. The remanent polarization (P r) obtained from positive-up negative-down measurements was high, exceeding 120 μC cm−2. The coercive field (E c) of Sc0.44Ga0.56N was approximately 3.6 MV cm−1 at 300 K, which decreased to 3 MV cm−1 at 473 K. We observed that regardless of the host material, the Sc concentration governed the E c value in Sc x Ga1−x N and Sc x Al1−x N, suggesting that the polarization switching started in the wurtzite unit cells containing Sc. Additionally, the E c of Sc x Ga1−x N was lower than that of Sc x Al1−x N when P r was equivalent.

Boosting of Magnetic, Ferroelectric, Energy Storage Efficiency, and Piezoelectric Properties of Zn Intercalated SrBi4Ti4O15-Based Ceramics.

An appropriate amount of Zn-ions are incorporated into the high Curie temperature bismuth layer-structure ferroelectric material to fabricate Sr0.2Na0.4Pr0.4Bi4Ti4O15:xwt%ZnO; (SNPBT:xZn), with x = 0, 0.10, 0.15, and 0.20 ceramic series to investigate the magnetic, ferroelectric, and energy storage efficiency and piezoelectric properties. Pure SNPBT and SNPBT:xZn ceramics have maintained their structure even after the intercalation of Zn-ions at the lattice sites of SNPBT. The addition of ZnO in SNPBT has improved the multifunctional properties of the material at x = 0.15. At room temperature, SNPBT:0.15Zn has shown a high relative density of 96%, exhibited weak ferromagnetic behavior along with a low saturation magnetization (Ms) of 0.028 emu/g with a low coercive field of 306 Oe, a high remnant polarization (Pr) of 9.04 µC/cm2, a recoverable energy density () of ~0.5 J/cm3, an energy conversion efficiency (η) of ~41%, a high piezoelectric co-efficient (d33) of 21 pC/N, and an impedance of 1.98 × 107 Ω, which are much improved as compared to pure SBT or pure SNPBT ceramics. Dielectric Constant (ɛr) versus temperature plots present the sharp peak for SNPBT:0.15Zn ceramic at a Curie temperature (TC) ~ 605 °C, confirming the strong ferroelectric nature of the ceramic. Moreover, SNPBT:0.15Zn ceramic has shown strong, piezoelectric, thermally stable behavior, which remains at 76% (16 pC/N) of its initial value even after annealing at 500 °C. The achieved results clearly indicate that SNPBT:0.15Zn ceramic is a promising candidate for future wide-temperature pulse power applications and high-temperature piezoelectric devices.

A Gradual Change in Al1-XScX N Ferroelectric Film upon Switching Reversal

Ferroelectric materials have been utilized for non-volatile memory applications [1]. Recently, Al1-x Sc x N (ASN) films were reported to exhibit ferroelectricity with a high remnant polarization of over 100 µC/cm2 which is attractive for future non-volatile memory [2]. The feasibility of FeRAM application has been confirmed based on material and electrical properties [3]. One of the issues of ASN films is the lack of reliability and endurance properties, as the number of switching cycles of 104 to 105 is the typical endurance of the ASN films before breakdown [4]. In this study, we infer the gradual change in the ASN film upon switching cycles.A 50-nm-thick ASN film with x of 0.22 was characterized with TiN electrodes at top and bottom. The as-fabricated film is self-polarized in an upward direction; the negative voltage applied to the top electrode triggers the switching reversal. Capacitance-voltage (C-V) characteristics, double sweeping the voltage to the negative, and then to the positive directions, were used to observe the switching voltage. A sinusoidal wave with an amplitude of 28 V at 2 kHz was used to switch the capacitor, ending with a positive voltage applied to the top electrode.The C-V curve for the as-fabricated sample (fresh), shown in figure 1, showed only a single peak capacitance for each sweep. The voltage at the peak capacitance during the negative sweep shifted from -20.8 to -17.4 V from the first to third sweep, larger than the shift during the positive sweep. This indicates that the switching voltage, or the coercive field, was reduced during the first negative sweep. After stressing the sample by 103-cycle switching, the C-V curve revealed two capacitance peaks in the negative direction, as shown in figure 2; the peak at -20.2 and -15.2 V are referred to as the peaks obtained in the first and third sweeps for the fresh device. The capacitance peak at -20.2 V gradually decreased moving to merge to the peak at -15.2 V. During this transition, little change of the peak in the positive region was observed, indicating that a gradual transformation in the ASN film upon switching reversal is happening only when the film is switched from upward to downward direction. We hypothesized the creation of nitrogen-vacancy (VN) during the switching, facilitating the movement of N atoms to reduce the coercive field. One can understand that the transformation is completed during the C-V measurement for the fresh sample as the time for the measurement is long.In conclusion, we observed a gradual change in the switching voltage upon switching reversal. A lower coercive field was found to gradually appear after switching, decreasing, and shifting the initial coercive field.

Sub-switching domain effect for analysis the non-linear dielectric behavior of (K0.49 Na0.49Li0.02) (Nb0.98Sb0.02)O3 ceramic based on Rayleigh model

The solid-state sintering technique has been implemented to synthesize (K0.5Na0.5NbO3)-0.02(LiSbO3) (KNN-LS) Pb-free ceramic. The crystal structure, dielectric and ferroelectric properties of the prepared material were investigated. Pure orthorhombic perovskite phase [I(220)/I(002) = 1.68] with Amm2 space group has been detected at room temperature for sintered ceramic. Two anomalous permittivity peaks corresponding to orthorhombic–tetragonal (O–T) phase transition at T = 175 °C and tetragonal–cubic (T–C) phase transition at T = 355 °C have been observed. At polymorphic phase transition, the Rayleigh model shown the extrinsic contributions caused by domain wall motion is about 80%, while the intrinsic contribution attributed to the lattice distortion is about 20%. Ferroelectric properties were investigated in a wide range of temperatures (RT-225)°C. The results shown a conductive material at high temperature due to the higher cation disorder and leakage current above PPT. The present results are interested for understanding the mechanism of t permittivity–temperature behavior of KNN-doped LS ions based on Rayleigh model. The large remnant polarization and low coercive field below PPT make the material a suitable candidate for energy storage application.

The effect of domain switching on the lattice symmetry and dielectric properties of (Bi0.5Na0.3K0.2)TiO3–0.2SrTiO3-(Ba0.8Ca0.2)TiO3 piezo-ceramic by poling field

The present study illustrates the effect of domain switching on the structural, dielectric, and piezoelectric properties of [0.75(Bi0.5Na0.3K0.2)Ti O3-0.2SrTi O3-0.05(Ba0.8Ca0.2)Ti O3] (i.e., BNKT- ST-BCT) Pb-free ceramic caused by poling effect. The sample has been synthesized by the solid reaction technique. The poling conditions were changed from (10–50 kV/cm) for 30 min at 100 °C. The pristine ceramic sample showed pseudo-cubic crystal structure, while tetragonal structure was detected for all the poled samples. The pristine sample showed a normal ferroelectric loop with a low coercive field (Ec =12 kV/cm) owing to the domain grow caused by domain wall displacement. The effect of poling field into Raman spectra showed variation the volume fraction of orthorhombic and tetragonal phases. Increasing the intensity of the tetragonal phase is related to the increase in lattice symmetry of the poled samples at a high poling field. Relaxor to paraelectric phase transition was observed at Burn's temperature (TB) of the un-poled sample, while the poled rates undergo a ferroelectric to relaxor phase transition at depolarization temperature (Td). In the regime of the sub-switching domain, the maximum permittivity was found to increase by poling field due to Rayleigh effect, while at high poling field it was observed to decrease due to tunability effect. The maximum current peak of relaxor to ferroelectric phase transition was observed to mitigate by increasing the poling effect. The converse piezoelectric coefficient, (d33∗) was achieved to be higher in the un-poled sample due to the lowest crystal symmetry in the absence of a poling effect. The existence of poling process leads to shrink both current peak and (d33∗) values, indicating the dominated of the tetragonal phase rather than the orthorhombic phase. Such results offer distinct features of an un-poled ceramic sample that make it suitable for different technological applications such as energy storage devices, sensors, and actuators.

Magnetic and Magnetostrictive Behaviors of Laves-Phase Rare-Earth-Transition-Metal Compounds Tb1-xDyxCo1.95.

The magnetic morphotropic phase boundary (MPB) was first discovered in Laves-phase magnetoelastic system Tb–Dy–Co alloys (PRL 104, 197201 (2010)). However, the composition-dependent and temperature-dependent magnetostrictive behavior for this system, which is crucial to both practical application and the understanding of transitions across the MPB, is still lacking. In this work, the composition-dependence and temperature-dependence of magnetostriction for Tb1−xDyxCo1.95 (x = 0.3~0.8) are presented. In a ferrimagnetic state (as selected 100 K in the present work), the near-MPB compositions x = 0.6 and 0.7, exhibit the largest saturation magnetization MS and the lowest coercive field HC; by contrast, the off-MPB composition x = 0.5, exhibits the largest magnetostriction, the lowest MS, and the largest HC. Besides, a sign change of magnetostriction is observed, which occurs with the magnetic transition across the MPB. Our results suggest the combining effect from the lattice strain induced from structure phase transition, and the influence of the MPB on magnetocrystalline anisotropy. This work may stimulate the research interests on the transition behavior around the MPB and its relationship with physical properties, and also provide guidance in designing high-performance magnetostrictive materials for practical applications.