Search

New energy vehicles and offshore wind power industries have a high demand for sintered Nd–Fe–B magnets with high intrinsic coercivity and high corrosion resistance. In this study, the magnetic properties, anticorrosion properties, and microstructure of Nd–Fe–B sintered magnets with the intergranular addition of low-melting-point eutectic Tb68Ni32 alloy powders were investigated. The aim is to determine if the addition of Tb68Ni32 could improve these properties. A low melting-point eutectic alloy Tb68Ni32 powders was prepared as a grain boundary additive and blended with the master alloy powders prior to sintering. The coercivity of the resultant magnets gradually increases from 1468 to 2151 kA/m by adding increasing amounts of Tb68Ni32. At the same time, the remanence first increases and then slightly decreases. After studying the microstructure and elemental composition of the Tb68Ni32 added magnets, it is found that the significant increase in coercivity and the negligible reduction in remanence is due to densification, improved grain orientation, a uniform and continuous boundary phase distribution, as well as the generation of a (Nd, Pr, Tb)2Fe14B “core–shell” structure surrounding the main-phase grain. Moreover, the corrosion resistance of the magnet is greatly improved owing to the enhancement of electrochemical stability, as well as the optimization of the distribution and morphology of the intergranular phase.

The table-like magnetocaloric effect is significant for the magnetic refrigeration applications above 20 K based on the Ericsson cycle. Herein, we prepared a series of Nd6Fe13Pd1–xCux (x=0.05, 0.1, 0.15) compounds by the arc-melting method. These compounds show the single crystalline phase in the tetragonal Nd6Fe13Si-type structure with the space group I4/mcm. A magnetic phase transition from ferromagnetism to antiferromagnetism and a metamagnetic transition from the antiferromagnetic state to the ferromagnetic state were observed in each of the compounds. The compounds exhibit table-like magnetocaloric effects with large refrigerant capacities. A constant ΔSM in a temperature span of 40 K in the Nd6Fe13Pd0.85Cu0.15 compound was observed. For a field change of 0–5 T, the peak values of –ΔSM for the Nd6Fe13Pd0.95Cu0.05, Nd6Fe13Pd0.90Cu0.10, and Nd6Fe13Pd0.85Cu0.15 compounds were estimated to be 4.8, 4.6 and 4.4 J/(kg·K) with corresponding refrigerant capacity values of 323, 331 and 316 J/kg, respectively. The obtained table-like magnetocaloric effects with large refrigerant capacities as well as fairly small thermal and magnetic hysteresis deem these series of compounds good candidates for single-phase magnetic refrigeration based on the Ericsson cycle.

In order to develop novel materials based on rare earth (RE) boride and/or transition metals, phase equilibria and thermodynamic information of the RE–B based alloys are indispensable. On the basis of experimental phase equilibria and thermodynamic properties, thermodynamic assessments of the RE–B (RE = La, Sm, Gd and Tb) binary systems were carried out by the CALPHAD (Calculation of Phase Diagram) method. Self-consistent parameters of the RE–B (RE = La, Sm, Gd and Tb) binary systems were obtained, which can be used to reproduce well the experimental data. Furthermore, in combination with the previous assessments of the RE–B binary systems in the literature, phase equilibria and thermodynamic properties of the RE–B (RE = La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm and Lu) binary systems are discussed systematically. The tendency of phase equilibria and thermodynamic information as a function of RE atomic number is demonstrated. In general, the enthalpy of mixing of liquid RE–B alloys and the enthalpy of formation of the RE–B intermetallic compounds become more and more negative with the increase in RE atomic number (except for La, Ce, Pr and Nd), while the phase transition temperatures for the RE–B intermetallic compounds increase gradually.

In this paper, a high-purity NdFe1-xNixO3 perovskite-type material was prepared by a simple sol method. At the same time, adjust the substitution content of nickel to achieve the purpose of adjusting the dielectric properties and magnetic properties. According to the respective instruments, as Ni is substituted into the NdFeO3, the crystal microstructure will change to a certain extent, and there is a certain causal relationship between the magnetic properties and the bonding. Therefore, by adding a certain amount of nickel, the dielectric properties and magnetic properties can be adjusted to a certain balance point. NdFe1-xNixO3 material has excellent microwave absorption performance. When x = 0.2, the minimum reflection loss value is −49.32, and the corresponding impedance matching value is 1, and the effective bandwidth is 2.2 GHz when the thickness is 5.0 mm. The material that adjusts the perovskite structure by Ni element is beneficial to make the microwave absorption peak move from high frequency to low frequency, which has a wider application range and is closer to civil, commercial, military and aerospace.

The poled (1−x) KNbO3–xLaNiO3−δ ferroelectric semiconductors obtained an enhanced visible-light photocatalytic hydrogen evolution rate of 642.0 µmol g−1 h−1, which is at least 16 times that of the unpoled sample (40.1 µmol g−1 h−1).

We investigated the magnetic properties, corrosion resistance, and microstructure of Tb6Fe13Cu-added Nd–Fe–B sintered magnets through the magnetic measurement device, electrochemical method, and microstructure analysis. The results show that doping Tb6Fe13Cu can not only effectively improve the intrinsic coercivity but also significantly improve the corrosion resistance of the magnet. An intrinsic coercivity from 15.01 to 21.40 kOe is achieved in magnet by increasing the additive amounts of Tb6Fe13Cu to 3 wt%, while the remanence and the maximum energy product decreased slightly. It was also found that as the amount of addition increases, the corrosion potential of the magnet gradually becomes positive. Further investigations reveal that the remarkable enhancement in coercivity and corrosion resistance was owing to the formation of a Tb-rich (Nd, Pr, Tb)2Fe14B shell structure, the optimization in distribution/morphology of intergranular phases, and the more stable RE-rich phase.

Microstructure and magnetic properties are systematically investigated to figure out what effect does the Cu content have on (Pr0.25Nd0.75)2Fe13.85-xCo0.1Ti0.05CuxB alloys in this work. The experimental result shows the optimal magnetic properties that the remanent magnetization Jr = 1.13 T, the coercivity Hcj = 588.56 kA/m, and the maximum magnetic energy product (BH)max = 260.66 kJ/m3 at the Cu content x = 0.6. However, it shows that Cu addition can promote the formation of the amorphous phase, which is an important reason for the coercivity decrease. Microstructure observation indicates that the reason for the magnetic property decrease is that the hard 2:14:1 magnetic phases and soft α-Fe phases display a state of irregular distribution with Cu content increasing.

The enhanced piezoelectric and ferroelectric properties of the tetragonal 0.67BiFeO3–0.33BaTiO3 (BF–33BT) ceramics without MnO2 doping or other dopants via tailoring sintering temperature (TS) and dwell time (td) are reported. All ceramics crystallized in a single tetragonal phase, independent of the adopted TS and td. As the TS or td is increased, the BF–33BT ceramics show an increase in grain size and in relative density, while TS > 980 °C or td > 6 h would result in more oxygen vacancies caused by Bi3+ evaporation and/or reduction of Fe3+ to Fe2+, along with a reduced relative density and an increased current leakage density. Because of the increased grain size, the higher relative density, and relatively less oxygen vacancies, high d33 = 151 pC/N and Pr = 25.9 μC/cm2 were achieved in tetragonal BF–33BT ceramics with TS = 980 °C and td = 6 h. In addition, large unipolar strain of 0.146% and $$d_{33}^{*}$$ =326 pm/V (40 kV/cm), as well as high TC = 427 °C were also obtained in the BF–33BT ceramics with TS = 980 °C and td = 6 h. Our studies indicate that the grain size, the relative density, and the oxygen vacancies play important roles for the piezoelectric properties of BF–33BT ceramics.

The influence of B-site complex ions substitution on the dielectric and piezoelectric properties of (Bi0.5Na0.5)0.93Ba0.07Ti1–x(W0.5Mg0.5)xO3 (BNBT–xWM) ceramics was studied in detail. X-ray diffraction patterns revealed that B-site substitution resulted in a phase transition from the tetragonal phase to pseudocubic phase. Ferroelectric to relaxor (FE-RE) phase transition temperature TF-R decreased with increasing (W0.5M0.5)4+ dopants, finally below room temperature. The destabilization temperature of piezoelectric constant d33, together with ferroelectric response was decreased with increasing x. However, the strains could be significantly enhanced with the addictive of (W0.5M0.5)4+, and a large strain of 0.325% with a normalized strain, d33* of 541.7 pm/V could be achieved for x = 0.04 ceramics [ergodic relaxor (ER) dominant]. The enhanced strains might attribute to the composition-induced NR–ER transition and high dynamic polar-nanoregions (PNRs), which strongly affecting piezoelectric and dielectric properties.

In this paper, polycrystalline samples of Bi1–xSmxFeO3 (x = 0, 0.05, 0.1, 0.15) were successfully synthesized by sol-gel method. The effects of Sm concentration on the crystal structure, morphology, chemical states, magnetic properties and microwave absorption performance were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), a vibrating sample magnetometer (VSM) and a Vector network analyzer (VNA), respectively. The results show that the rare earth Sm doping causes the crystal structure to change. When x ≤ 0.1, Bi1–xSmxFeO3 is the distorted rhombohedral structure with space group R3c. With the increase of Sm doping amount to x = 0.15, the phase structure of Bi1–xSmxFeO3 changes from rhombohedral structure to cubic structure with the space group Pm 3 ¯ m. The particle size decreases with the increase of the Sm doping amount. The analysis results show that Sm doping can effectively reduce the oxygen vacancies and significantly improve its magnetic properties. The results exhibit that moderately doped rare earth Sm element can effectively improve microwave absorption properties of Bi1–xSmxFeO3 powders. When Sm doping amount of x is 0.1, the Bi0.9Sm0.1FeO3 compound has good microwave absorption performance, and the minimum reflection loss value of Bi0.9Sm0.1FeO3 powder reaches about −32.9 dB at 11.7 GHz, and its effective absorption bandwidth (RL

The vertical sections of the La−Fe−B system were investigated using electron probe microanalysis and differential thermal analysis. Based on the microstructures and phase compositions of the as-cast and equilibrium alloys, together with their heat flow−temperature curves, phase diagrams for three vertical sections were drawn: LaxFe82By (x+y=18), LaxFe70By (x+y=30) and LaxFe53By (x+y=47), where x and y represent mass fraction of La and B, respectively, % . Additionally, according to the phase diagrams, the compound La2Fe14B was identified as a stable phase at high temperatures. It was found to be stable between 926.2 and 792.6 °C; at low temperatures, however, it decomposed into α-La, α-Fe and LaFe4B4, according to the reaction La2Fe14B→α-Fe+α-La+LaFe4B4.

Using published and presently calculated diffusivities, a reliable and self-consistent atomic mobility description of the liquid and fcc phases in a Nd-Fe-B system is established by DIffusion-Controlled TRAnsformation software. Based on the obtained atomic mobility-coupled thermodynamic descriptions of the Nd-Fe-B system, a wheel speed-dependent solidification diagram for a model Nd2Fe14B alloy is constructed, which allows us to examine the influence of wheel speed on the solidification behavior of the quenching Nd2Fe14B alloy. According to the theoretically obtained solidified microstructures and their relationship with the magnetic properties, the optimal wheel speed when melt-spinning the quenching Nd2Fe14B ribbons is determined to be 35 m/s. The experimental microstructural characterizations and magnetic hysteresis loop measurements confirm that the ribbon prepared at a wheel speed of 35 m/s exhibits the best comprehensive magnetic properties because the remaining bcc-Fe phase is significantly suppressed and the main Nd2Fe14B phase was well refined to an ultrafine-grained microstructure. The grain refinement mechanism of the main phase in the ribbons is also described.