Typical Hysteresis Loops Research Articles

Controlling the magnetoelectric coupling in Ni/BiFe0.95Mn0.05O3 with a dielectric spacer

In artificial multiferroic heterostructures combining ferromagnetic transition metal films and bismuth ferrite layers the electric field control of the magnetic state is generally achieved through interface exchange coupling. Here we report a reversible and non-volatile magnetoelectric (ME) effect in Ni/ BiFe0.95Mn0.05O3 bilayers originating primarily from a strain-transfer mechanism. The non-volatility of the ME effect is explained by an asymmetric piezoelectric strain response of the ferroelectric BiFe0.95Mn0.05O3 film with respect to the applied electric field, yielding two different states at remanence. We further show that the piezoelectric properties and the ferroelectric domain structure of the BiFe0.95Mn0.05O3 film can be controlled by tuning the screening of the polarization charge at the interface through an interleaved dielectric SrTiO3 spacer. As the dielectric spacer thickness is decreased, the strain-mediated ME response evolves from the typical butterfly-like hysteresis loop towards a rectangular shape, thereby making such artificial multiferroics suitable for non-volatile memory applications.

Exploring magnetoelectric coupling in trilayer [Ba(Zr0.2Ti0.8)O3- 0.5(Ba0.7Ca0.3)TiO3]/ CoFe2O4/[Ba(Zr0.2Ti0.8)O3- 0.5(Ba0.7Ca0.3)TiO3] thin film

Magnetoelectric (ME) heterostructures with strong ME coupling at room temperature are of great importance due to their promising applications in next-generation devices. Here, lead-free [Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3]/CoFe2O4/[Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3] (abbreviated as (BZT-0.5BCT)/CFO/(BZT-0.5BCT)) trilayer thin film has been deposited on Pt/Ti/SiO2/Si (100) substrate by pulsed laser deposition technique. Dielectric properties of trilayer thin film show the relaxor behavior and high value of dielectric constant (∼2.2 × 103) with low dielectric loss (∼0.16) at frequency 100 Hz at room temperature. Typical ferroelectric and magnetic hysteresis loops were found with large electric polarizations (Ps = 12.14 μC/cm2, Pr = 6.0 μC/cm2) and magnetization (Ms = 246 emu/cc and Mr = 66.6 emu/cc), respectively. The change in PE loop on the application of magnetic field represents the strong ME coupling. The high value of ME coefficient (αME∼0.74 V/cm.Oe) was detected at room temperature which indicates its potential application for multifunctional ME devices.

Investigation of magnetic and ferroelectric properties along with the magnetoelectric coupling behavior for asserting a room temperature bi-phase composite as multiferroics

Various composites of nominal composition (1-x)Ba0.95Ca0.05TiO3 + xLi0.1Cu0.1Co0.1Zn0.6Fe2.1O4 have been prepared and studied thoroughly. X-ray diffraction and Rietveld refinement confirmed the presence of Ba0.95Ca0.05TiO3 and Li0.1Cu0.1Co0.1Zn0.6Fe2.1O4 phases in the composites. The microstructures have been investigated by field emission scanning electron microscopy. Temperature dependent dielectric constant shows two peaks, one is at 150 °C and another at 270 °C for x = 0.10 composite which resembles the characteristic ferroelectric and ferromagnetic transition peaks. A gradual progression of ferro-para electric transition towards room temperature is observed with doping. The non-Debye type dipole relaxations have been found. The linearity in the log(σAC) vs. log(ω) plots indicate that conduction is due to small polaron hopping. The real part of initial permeability increases with growing ferrite concentration but the cut-off frequency decreases. The magnetic property is also enhanced with doping content. The typical ferroelectric hysteresis loops have also seen with the addition of Li0.1Cu0.1Co0.1Zn0.6Fe2.1O4 up to x = 0.40. The impedance values are found to decreases in the Nyquist plots. The magnetoelectric voltage coefficient is obtained 287 × 103 V/mT for x = 0.15 at room temprrature. We found both ferromagnetic and ferroelectric hysteresis loops at room temperature. So, it confirms that the composites exhibit room temperature multiferroicity. This type of composites offers variety of opportunity for multifunctional devices application like hetero-structured read / write memory devices, switching devices and magnetic field sensing devices.

Microstructure and magnetic interactions of Co2+ substituted NiCuZn ferrites

Nickel-Copper-Zinc ferrites are state-of-the-art dielectric materials with enhanced electromagnetic properties. Herein, we report, physicochemical and magnetic properties of Co2+ substituted NiCuZn ferrites of the series Ni0.25-xCoxCu0.30Zn0.45Fe2O4 (x = 0.00, 0.05, 0.01, 0.15, 0.20 and 0.25). The adopted synthesis method is the facile sol–gel auto combustion route with glycine as a reducing agent. X-ray diffraction (XRD) signatures revealed the cubic spinel structure, with a decrease in the lattice constant (a) due to a smaller ionic radius of Co2+ (0.72 Å) replacing Ni2+ (0.74 Å) ions. The optical properties of the ferrites are discussed in detail, viz. refractive index (η), reflectivity (R), the velocity of IR waves (v), and jump rates (J1, J2, and J). EDAX analysis indicated the elemental composition of ferrite samples as per the chosen stoichiometry. The microstructural analysis (SEM and TEM) depicts the dense microstructure with the average grain size of 38–95 nm. The samples exhibit a typical magnetic hysteresis loop at room temperature with low coercivity values confirming the soft magnetic nature. The maximum MS = 56 emu/gm was observed for the ferrite sample with x = 0.20. Temperature-dependent initial permeability at a constant frequency (1 MHz) showed the drop in the permeability values with increasing Co2+ content, whereas the values of Tc remain fairly unchanged.

Elastic, electronic and electrocaloric properties near room temperature in [formula omitted]-doped [formula omitted] from first-principles calculations

Ferroelectric materials are attractive candidates for potential solid-state refrigeration. Their useful broad applications require investigation of several properties. However, the magnitude corresponding to electrocaloric effect (ECE) is seemingly too small. Insight from a theoretical approach is needed to provide support through theoretical description, leading mainly to better understanding and prediction of the electrocaloric performance, as well as additional properties that might be useful. Here, we investigate the elastic, electronic, thermoelectric, and ferroelectric properties as well as ECE of SnTiO3 by utilizing first-principles calculations and effective Hamiltonian. From the calculations toward a higher symmetry direction, the direct band gap is obtained. In addition, we have comprehensively investigated the effect of Mn-doping on the electronic and thermoelectric properties of SnTiO3 to achieve a better understanding of this material. The polarization, pyroelectric coefficient, changes in entropy ΔS and adiabatic temperature ΔT are examined in detail as a function of temperature. This work also reveals the contribution with particular attention of the applied electric field especially on the magnitude of ECE, resulting in slightly anomalous volume expansion. Typical hysteresis loops are observed to confirm the order-disorder phase transition. An enhancement route of the ECE is elucidated, which may open the door for more discussions and practical applications.

Surface modification of magnetic TiO2 core-shell with doped cerium for enhancement of photocatalytic performance

The core-shell structure of Ce-doped TiO 2 @SiO 2 @(Ni-Cu-Zn) ferrite noted of CTSF as composite nanoparticles (NPs) was synthesized using a modified sol-gel method. The physicochemical properties of as-prepared products were characterized completely by X-ray diffraction (XRD), Brunauer-Emmit-Teller (BET), X-ray photoelectron spectroscopy (XPS) and superconducting quantum interference device (SQUID), serially. Meanwhile, assessment of the photocataly s tic activity of catalyst was performed by ultraviolet-visible spectrometry (UV-vis). The results of the study show that the anatase phase related to the TiO 2 structure was constructed on the outer shell coating of composite NPs. However, the second phase associated with the Ce structure was not easy to be detected on the XRD pattern, confirming that the doping Ce had been incorporated into the TiO 2 crystal structure. The mesoporous structure of Ce-doped TiO 2 layers was demonstrated by the type IV isotherm and H3 type hysteresis loop. The homogenous pore size was generated with the specific surface area up to 111.916 m 2 /g and 0.241 cc/g of pore volume. The stoichiometry of the chemical composition formed with fewer defects on the surface of TiO 2 layers was exhibited by the symmetry curve of Ti 2p 3/2 and Ti 2p 1/2 peaks of XPS spectra. Meanwhile, the redox couple corresponding to Ce 3+ /Ce 4+ was incorporated inside the thin TiO 2 coating. Furthermore, the catalyst magnetic NPs can be also separated by using an external magnetic field from the reaction system. The product performance associated with the degradation efficiency was achieved to be 50 % in the aqueous solution of methylene blue (MB)

Intermixing of Fe and Cu on the atomic scale by high-pressure torsion as revealed by DC- and AC-SQUID susceptometry and atom probe tomography

The capability of high-pressure torsion on the preparation of supersaturated solid solutions, consisting of Cu-14Fe (wt.%), is studied. From microstructural investigations a steady state is obtained with nanocrystalline grains. The as-deformed state is analyzed with atom probe tomography, revealing an enhanced solubility and the presence of Fe-rich particles. The DC-hysteresis loop shows suppressed long range interactions in the as-deformed state and evolves towards a typical bulk hysteresis loop when annealed at 500∘ C. AC-susceptometry measurements of the as-deformed state reveal the presence of a superparamagnetic blocking peak, as well as a magnetic frustrated phase, whereas the transition of the latter follows the Almeida-Thouless line, coinciding with the microstructural investigations by atom probe tomography. AC-susceptometry shows that the frustrated state vanishes for annealing at 250∘ C.

Unraveling the electronic, optical, ferroelectric, and electrocaloric properties of [formula omitted] thin film: Insight from first-principles effective Hamiltonian

In this work, electronic, optical, dielectric and ferroelectric properties of PbxSr1-xTiO3 (PST) thin film are systematically investigated. This system is studied from first-principles computations using density functional theory (DFT) and effective Hamiltonian. In this regard, the influence of Pb doping on the above properties is elucidated to unravel a global description of this material. From the calculations along the higher symmetry direction, and upon substitution of Sr content, a direct band gap is obtained. Concerning the optical properties, the curves of refractive index revealed a systematic variation with composition. The results were compared with other reviews and showed a good agreement. Through a detailed analysis, investigations of several parameters are reported. However, an appropriate level of Pb doping can provide tremendous informations about this material, representing an important step toward deeper understanding for furthering knowledge, which may open the door for practical applications. This work reveals the contribution of Pb content especially on the phase transitions. The increase in the concentration of Pb shifts the critical temperature towards higher temperature and evolves the dipoles to switch for a large temperature range, resulting a large tetragonal (ferroelectric) phase and anomalous volume expansion, which in turn could improve the ferroelectric transition temperature. The dielectric constant, polarization and pyroelectric coefficient are examined as a function of the temperature. A typical hysteresis loops were clearly observed to confirm the ferroelectric-paraelectric phase transition. Besides, the electrocaloric effect (ECE) of PST thin film is also predicted with particular attention to the applied electric field and concentration x. Our calculations also revealed that PbxSr1-xTiO3 thin film exhibits a large room-temperature adiabatic temperature change (ΔT), which largely depends on the Pb content. The increase of Pb composition improves the adiabatic temperature change and enlarges its maximum at a relatively higher temperature. An enhancement regarding the ECE may potentially open the door for practical cooling device applications.

Magnetic Modification and the Mechanism of Tb‐Phthalocyanine Single Molecule Magnets Prepared by a High Yield Method

Lanthanide single‐molecule magnets are the most promising materials to be applied in the future spintronics applications. In this report, we firstly synthesize double‐decker Phthalocyanines (Pc), TbPc2 single‐molecule magnets and paramagnetic YPc2 by a straightforward solvothermal route with a yield up to 16 %, which is three times larger than that of conventional method. Their crystal structures and properties are systematically characterized by the matrix‐assisted laser desorption ionization–time‐off light mass spectrometry, X‐ray diffractometer, Ultraviolet–visible spectra, Fourier transform infrared spectra, X‐ray photoemission spectroscopy, near‐edge X‐ray absorption fine structure (NEXAFS) spectroscopy, Inductive Coupled Plasma Emission Spectrometer and magnetic measurements. The NEXAFS spectroscopy confirms that a strong peak at 401 eV emerges not YPc2 but TbPc2, clearly indicating the different electronic structures of YPc2 and TbPc2. A typical hysteresis loop of single molecule magnet is observed for TbPc2. While, YPc2 shows a paramagnetic character. The SMM property of TbPc2 modified by introducing YPc2 was studied in detail. The maximum hysteresis area appears for the sample with Tb/Y = 7:3, which obviously demonstrates the concentration of YPc2 affects magnetic relaxation process by varying the intermolecular interactions of TbPc2. The barrier energy fitted from the results of alternating‐current magnetic susceptibility is 740 K for TbPc2 and 781 K for the sample with Tb/Y = 7:3, further indicating that the isolation of neighbor Tb ions by Y ions could slow down the flip of magnetic dipole.

An enhanced constitutive model for the nonlinear mechanical behavior of the elastic-porous metal rubber

This work aims to develop an enhanced constitutive model to efficiently capture the nonlinear mechanical properties of the elastic-porous metal rubber such as hysteresis characteristics and variable stiffness behavior. As a key fabrication variable, the normal distribution of the three-dimensional interlocked angle is introduced to describe the orientation arrangement of the metal wires and to develop an equivalent stiffness model of the elastic-porous metal rubber. Integrating with the evolution of the typical hysteresis loops, different function-fitting methods are used to describe the mechanical behavior under loading and unloading paths. In particular, the effect of displacement amplitude on the mechanical properties in the unloading process is addressed. From the results, it is observed that the hysteresis loop curves predicted by the enhanced constitutive model show a great agreement with the experimental results. The enhanced constitutive model has better prediction accuracy as compared to the other constitutive models (such as the micro-spring model and the porous material model). In addition, the anisotropic behavior and the dynamic property associated with stiffness and energy dissipation of elastic-porous metal rubber are analyzed and discussed.

Synthesis of Ni80Fe20 permalloy antidots for high storage ferroelectric memories

Here, we report a successful synthesis of Ni80Fe20 permalloy antidots developed by using anodic alumina membranes. Regular array of antidots with 20 nm size and 55 nm dot to dot spacing were obtained. The purpose for developing antidots is to provide accurate pinning sites with reduced depolarization fields suitable for ferroelectric memories or pyroelectric detectors. Ni80Fe20 permalloy attains the hexagonal morphology occupied from the anodic alumina membranes as can be seen from field emission scanning electron microscope images. X-ray diffraction confirms the fcc texture of Ni80Fe20 permalloy. Current-voltage characteristics provide evidence of a non-linear and asymmetric behavior of antidots. Typical polarization hysteresis loops were obtained showing enhanced ferroelectric properties for these antidots.

Intermixing of Fe and Cu on the Atomic Scale by High-Pressure Torsion as Revealed by Dc- and Ac-Squid Susceptometry

From microstructural investigations a steady state is obtained with nanocrystalline grains. The DC-hysteresis loop shows suppressed long range interactions in the as-deformed state and evolves towards a typical bulk hysteresis loop when annealed at 500°C. AC-susceptometry measurements of the as-deformed state reveal the presence of a superparamagnetic blocking peak, as well as a magnetic frustrated phase, whereas the transition of the latter follows the Almeida-Thouless line. AC-susceptometry shows that the frustrated state vanishes for annealing at 250°C.

A Three-Dimensional Lead Halide Perovskite-Related Ferroelectric

Three-dimensional (3D) organic-inorganic lead halides represented by [CH3NH3]PbI3 perovskite have attracted great interest for their diverse functional properties and promising optoelectronic applications. However, 3D lead halides are still very rare and their ferroelectricity remains controversial. Here, we report an unprecedented 3D lead halide perovskite-related ferroelectric [2-trimethylammonioethylammonium]Pb2Cl6 ([TMAEA]Pb2Cl6), which contains a 3D lead chloride framework of corner- and edge-sharing PbCl6 octahedral, with the [TMAEA]+ cations occupying the voids of the framework. [TMAEA]Pb2Cl6 shows a ferroelectric-to-paraelectric phase transition with the Curie temperature as high as 412 K, a typical ferroelectric hysteresis loop at 293 K with a spontaneous polarization of 1 μC/cm2, and a clear ferroelectric domain switching. To the best of our knowledge, [TMAEA]Pb2Cl6 is the first 3D lead halide showing such an excellent ferroelectricity. Additionally, it also exhibits semiconducting property with a direct bandgap of 3.43 eV. This finding enriches the family of 3D hybrid lead halides, and inspires the exploration of 3D lead halide ferroelectrics.

Structure and dielectric properties of Sm3+ modified Bi4Ti3O12- SrBi4Ti4O15 intergrowth ferroelectrics

Novel samarium modified intergrowth ferroelectric ceramics, namely Bi4Ti3O12-SrBi4Ti4O15, were synthesized by conventional solid state reaction method and sintered at 1100°C for 5 h. X-ray diffraction studies revealed the formation of a single phase with the signature of intergrowth oxide and plate like morphology was observed by scanning electron microscopic analyses. The orthorhombicity, the grain size and transition temperature were found to decrease with the increase of Sm content. The dielectric and modulus measurements were performed at different temperatures and frequency ranges. The transition temperature was found to be around 500 °C. The variations of imaginary part of modulus and dielectric constant with the temperature showed diffuse phase transition. The results are corroborated to the defect based mechanism and Curie deviation factor was evaluated by using the modified Curie-Weiss law. Polarization-electric filed curves displayed a typical narrow hysteresis loop at room temperature by applying an electric field of 70 kV/cm. However, above room temperature the hysteresis loop area was found to be increased. The overall results revealed that the complex dipoles and oxygen vacancies are playing a dominant role in the dielectric and electrical properties, and therefore the adopted intergrowth processing was found to be an effective approach to obtain potentially good ferroelectric materials.

A Sulfonated Porous Polymer as Solid Acid Catalyst for Biofuel Synthesis and Chemical Fixation of CO2

AbstractDeforestation and uncontrolled emission of carbon dioxide (CO2) through abundant use of fossil fuels result global warming. This serious threat to the atmosphere has deeply motivated the researchers to develop new strategies for chemical fixation of CO2 and biofuel synthesis. Here we report the sulfonated porous polytriphenylamine (SPPTPA‐1, BET surface area of 664 m2 g−1, pore volume 0.386 cc g−1) as an efficient heterogeneous catalyst for the synthesis of cyclic carbonates via CO2 fixation into epoxides. SPPTPA‐1 catalyst contains pores with dimension of 1.8‐2.0 nm, which produced a H1 type hysteresis loop in N2 adsorption/desorption isotherm. The porous catalyst is thermally stable upto 196 °C. The synthesized SPPTPA‐1 catalyst contains large amount of surface acidic sites. Further, it catalyzes the esterification reaction of levulinic acid, long chain fatty acids and dicarboxylic acids due to presence of its acidic sites. This solid acid catalyst SPPTPA‐1 showed excellent recycling efficiency upto 5 times in all these demanding reactions.

Pore characteristics of the lower Sinian Doushantuo Shale in the Mid-Yangtze Yichang area of China: Insights into a distinct shale gas reservoir in the Neoproterozoic formation

The Lower Sinian Doushantuo Shale comprises the oldest Neoproterozoic shale gas reservoir in the Middle Yangtze Yichang area of China, which makes the study of their pore characteristics critical to future shale gas exploration and exploitation. Geochemical, petrographical, and pore characteristics are studied in detail, with focused ion beam scanning electron microscopy (FIB-SEM) image analysis to further support and confirm the interpretations of the nano-scale pore structure characteristics. High total organic carbon (TOC) content, high thermal maturity, and considerable brittle mineral content indicate promising potential of the Doushantuo shale. High TOC samples suggest elevated micro-meso porosity, and H2(b) and H3 type hysteresis loops indicate inkbottle, slit-like, and flake-like pore types. Significant inorganic pores are commonly observed in dolomite, pyrite, and apatite, which are characterized by diamond or irregular shapes, with pore diameters ranging from 5 nm to 1000 nm as a result of the interaction between the minerals and the acidic organic fluids. Clustering organic matter (OM) pores are observed with pore diameters ranging from 5 nm to 50 nm; they are characterized by sponge-like, elliptical, and alveolate shapes, which indicate minor organic matter (OM) pores. More substantial organic matter (OM) pores can also be found around or between the pyrite and apatite. Fractures can be clearly observed between the organic matter and minerals with lengths of approximately 10 μm and 50 nm in width, which serve as conduits for shale gas migration. The pores in the Doushantuo Shale are dominated by inorganic pores and minor organic matter (OM) pores, which are different from the pore structure of the Wufeng-Longmaxi Shales in the Sichuan Basin. The Doushantuo Shale organic matter (OM) pores are much smaller and more densely distributed than those in the Wufeng-Longmaxi Shales. The different organic matter origins of these two shales have caused distinct organic matter (OM) pore-development mechanisms. Organic matter (OM) pores and inorganic pores could contribute to the volume of the adsorbed gas and free gas, respectively, which provide significant reservoir space in the Lower Sinian Doushantuo Shale in the Yichang area.

Effect of Controlled Oxygen Vacancy on H2‐Production through the Piezocatalysis and Piezophototronics of Ferroelectric R3C ZnSnO3 Nanowires

AbstractThis study is the first to demonstrate that ferroelectric R3c LiNbO3‐type ZnSnO3 nanowires (NWs), through the piezocatalysis and piezophototronic process, demonstrate a highly efficient hydrogen evolution reaction (HER). The polarization and electric field curves indicate that ZnSnO3 NWs exhibit typical ferroelectric hysteresis loops. Time‐resolved photoluminescence spectra reveal that the relaxation time increases with the increasing concentration of oxygen vacancies. Moderated 3H‐ZnSnO3 NWs (thermally annealed for 3 h in a hydrogen environment) have the longest extended carrier lifetime of approximately 8.3 ns. The piezoelectricity‐induced HER, via the piezocatalysis process (without light irradiation), reaches an optimal H2‐production rate of approximately 3453.1 µmol g−1 h−1. Through the synergistic piezophototronic process, the HER reaches approximately 6000 µmol g−1 in 7 h. Crucially, the mechanical force–induced spontaneous polarization functions as a carrier separator, driving the electron and hole in opposite directions in ferroelectric ZnSnO3 NWs; this separation reduces the recombination rate, enhancing the redox process. This theoretical analysis indicates that the photocatalytic and piezocatalytic effects can synergistically enhance piezophototronic performance through capitalizing on well‐modulated oxygen vacancies in ferroelectric semiconductors. This study demonstrates the essential role of this synergy in purifying water pollutants and converting water into hydrogen gas through the piezophototronic process.

Hydrothermal synthesis of neodymium oxide nanoparticles and its nanocomposites with manganese oxide as electrode materials for supercapacitor application

Neodymium and manganese oxide-based nanocomposites (Nd2O3/Mn3O4-0, Nd2O3/Mn3O4-1, and Nd2O3/Mn3O4-2) along with pure nanoparticles of Nd2O3 have been synthesized by the hydrothermal process. X-ray diffraction analysis presents that nanocomposites exhibit the mutual effect of hexagonal and tetragonal crystal structures of Nd2O3 and Mn3O4 respectively. Field emission scanning electron microscopic results display the interconnected Nd2O3 nanoparticles and irregular nanograins of Mn3O4. Energy dispersive x-ray spectroscopy proves the presence of constituting elements in the prepared materials. A type IV isotherm with H3 type hysteresis loop and pore size in the range of 30–45 Å, confirms the mesoporosity of all the prepared materials by nitrogen adsorption/desorption analysis. Electrochemical results display that Nd2O3/Mn3O4-1 electrode with mass ratio 63:37, owns excellent specific capacitance of 205.29 F g−1 at a scan rate of 5 mV s−1 as compared to other electrodes. This pseudocapacitance of Nd2O3/Mn3O4-1 electrode is likely ascribed to the pragmatic synergistic effects among the redox-active Nd2O3 and Mn3O4 metal oxides. The cycling stability of 67% over long cycles at 50 mV s−1 as well as high-coulombic efficiency of 99.64% at 5A g−1, making the Nd2O3/Mn3O4-1 electrode as an auspicious electrode material for supercapacitor applications.

Adsorption pore structure and its fractal characteristics of coals by N2 adsorption/desorption and FESEM image analyses

The adsorption pore structure and its fractal characteristics of coals (0.69–2.79% Ro,m) were investigated by N2 adsorption/desorption and field emission scanning electron microscopy. First, organic matter (OM) pores and interparticle pores (InterP) with various shapes are distinguished in different rank coals. The OM pores present irregular shapes in low-/middle-rank bituminous coals, and circular, oval and slit shapes in high-rank bituminous coal and anthracite with width from 50 nm to 2 μm. In contrast, the InterP pores show polygonal/elongated shapes and exist between mineral grains or mineral and OM with width >100 nm. Second, the coals with H1 type hysteresis loop of N2 adsorption/desorption isotherms are favorable for gas adsorption due to large pore surface area, whereas coals with H2 and H3 types are conducive to gas desorption and diffusion because of open pores with good connectivity. Moreover, the fractal dimension of pore shape was obtained from FESEM images and ranges from 1.068 and 1.30, indicating the adsorption pore shape is relatively regular. The surface and volume fractal dimensions of micropores and mesopores were calculated from the N2 adsorption data on the basis of surface fractal model and FHH model, respectively. The fractal dimension of micropore and mesopore surface respectively ranges from 2.18 to 2.69 and 1.78 to 2.41, whereas that of micropore and mesopore volume respectively ranges from 2.18 to 2.67 and 2.29 to 2.79. The pore structure and coal composition during different coalification stages have specific effects on the fractal characteristics of pore shape, surface and volume.

Net-shaped barium and strontium ferrites by 3D printing with enhanced magnetic performance from milled powders

Net-shaped hexagonal barium and strontium ferrites with desirable shapes have been successfully fabricated by the extrusion-based three-dimensional (3D) printing. The influence of milling and calcination conditions on magnetic properties of as-printed hexaferrites are systematically investigated by vibrating sample magnetometry (VSM). The typical ferromagnetic hysteresis loops are observed, revealing that the resulting bulk ferrites derived from the preliminary milled powders are prefect hard magnetic materials. In particular, it is clear that the saturation magnetization is very close to the theoretical values after calcinations. Moreover, the coercivity can be effectively enhanced in the range of 4–6 kOe upon thermal treatment, which is a much higher value compared to ferrites prepared by the conventional ceramic processing. More importantly, the maximum energy product can be significantly improved to as high as around 2.5 MGOe for the 3D-printed strontium ferrites. This is attributed not only to fine precursor powders subjected to mechanical milling, but also to the optimized annealing for grain growth with sizes near the critical single domain limit. Overall, the fabrication of bulk ferrites derived from milled powders using the 3D printing is attractive for the large-scale applications, and may also pave the way for some specific applications, for instance, magnetic separation for nanoparticles.