Hardening of K0.5Na0.5NbO3 lead-free ceramics by adding Ag2O and CuO and crystal-orientation behavior of their powders under a high magnetic field

Rare earth (RE) elements (Pr, Sm) doped K0.5Na0.5NbO3 (KNN) lead-free ceramics were fabricated using conventional solid-state reaction method and their properties were investigated. The X-ray methods indicate that Pr and Sm ions diffuse into the KNN lattice to form new homogenous solid solutions. After the doping of RE elements, the grain size decreases obviously and the phase structure translates from orthorhombic to pseudo cubic phase. The RE ions enter into the A-site of the KNN lattice to create new A-site vacancies, exhibiting “soft” characteristics. Existence of two semicircular arcs represents both grain and grain boundary property of the materials. The results of Ea indicate that oxygen vacancies dominate the conductivity properties of the ceramics from 425 to 525 °C The photoluminescence spectra of KNN + Pr exhibits orange emissions. Both the KNN + Sm and KNN + Pr/Sm ceramics exhibit yellowish green emission upon 406 nm light excitation. RE elements Pr and Sm-doped KNN ceramics may take an important role in many fields as multifunctional materials.

The rare–earth giant magnetostrictive materials are one kind of the most important functional materials now. The rare–earth giant magnetostrictive materials of TbFe2 and Tb0.27Dy0.73Fe1.95(R–Fe) alloys were firstly used in sonar system in military. Now, the applications of these two alloys have been developed widely in both industry and civil fields, such as magnetomechanical transducers, actuators, adaptive vibration control systems, and so on. The TbFe2 and Tb0.27Dy0.73Fe1.95 alloys both have the C15–type cubic Laves phase structure, which has strong magnetic anisotropy. This causes that the alloys exhibit different magnetostrictive properties along different crystal orientations. So, the preparation of high orientation degree magnetostrictive materials has a great of importance. In this work, it is predicted that the magnetostricive property of these two alloys can be enhanced with high magnetic field during heat treatment around their Curie and eutectic points. Therefore, a high magnetic field up to 11.5 T was imposed on these two kinds of R–Fe alloys during heat treatment at different temperatures in the experiments. Then the effects of high magnetic field on the crystal orientation, morphology and magnetostriction were analyzed in detail by XRD, metallographic microscope, and static resistance strain gauge. Also, the relationship between structure * K`W}h=dL+ 51006020, 51174056, KPe==osy3H3L+ 2011CB612206 'Jv T= }o9L+ N120409001, N120509001 ^W X: ℄A : 2013–05–28, X` ℄A : 2013–07–24 m8Nb : , ,, 1982 2m, zm DOI: 10.3724/SP.J.1037.2013.00289 9 AE` : KH0[A u TbFe2 ) Tb0.27Dy0.73Fe1.95 ,fl TO / [!)HEj _0^ K 1149 and property is discussed. The results showed that high magnetic field didn’t change the orientation of the R–Fe alloys, but the orientation degree had a great improvement after heat treatment. The phase composition of the two alloys had no change. However, the heat treatment with a magnetic field up to 11.5 T distinctly reduced the rare–earth phase of TbFe2 and obviously increased the magnetic phase. In addition, the magnetostrictive property of TbFe2 alloy increased after the heat treatment with high magnetic field. But for Tb0.27Dy0.73Fe1.95 alloy, the magnetostriction was not obviously enhanced. The reason for the improvement of the magnetostriction is that the Zeeman energy caused by high magnetic field increased the total Gibbs free energy of the system, which made the random orientation in crystals orient along the 〈113〉 direction, and enhanced the magnetostriction of the R–Fe alloys.

Lead free piezoelectric materials are being intensively investigated in order to substitute lead based ones, commonly used in many different applications. Among the most promising lead-free materials are those with modified NaNbO3, such as (K, Na)NbO3 (KNN) and (Ba, Na)(Ti, Nb)O3 (BTNN) families. From a ceramic processing point of view, high density single phase KNN and BTNN ceramics are very difficult to sinter due to the volatility of the alkaline elements, the narrow sintering temperature range and the anomalous grain growth. In this work, Spark Plasma Sintering (SPS) and high-energy ball milling (HEBM), following heat treatments (calcining and sintering), in oxidative (O2) atmosphere have been used to prepare single phase highly densified KNN (“pure” and Cu2+ or Li1+ doped), with theoretical densities ρth > 97% and BTNN ceramics (ρth ~ 90%), respectively. Using BTTN ceramics with a P4mm perovskite-like structure, we showed that by increasing the NaNbO3 content, the ferroelectric properties change from having a relaxor effect to an almost “normal” ferroelectric character, while the tetragonality and grain size increase and the shear piezoelectric coefficients (k15, g15 and d15) improve. For KNN ceramics, the results reveal that the values for remanent polarization as well as for most of the coercive field are quite similar among all compositions. These facts evidenced that Cu2+ may be incorporated into the A and/or B sites of the perovskite structure, having both hardening and softening effects.

High magnetic field is an important research condition which can provide great opportunities for the development of many subjects. Since 1913, there are 19 Nobel Prizes which are related to high magnetic field. Scientific research under high magnetic field involves a large amount of subjects and various scientific issues. In many research areas such as the quantum transport in semiconductors, Fermi surface measurements, the study of the upper critical field of high temperature superconductors, nuclear magnetic resonance study etc., high magnetic field is an essential condition. Therefore, the scientific research under high magnetic field is always the frontier. In this review, the cutting-edge scientific issues under high magnetic field are presented. The issues in physics include the fractional quantum Hall effect in graphene, the quantum oscillations in black phosphorus, the topological insulator Bi2Se3, the Weyl semimetal NbP, the quantum ordering in non-conventional superconductor, the magnetic field induced new superconducting phase, the magnetic field induced metamagnetism transition, the quantum effect of low dimensional materials, the spin frustration, etc. In chemistry and material science, the focuses are magnetic field induced new chemical reaction, control of reaction routes, the reaction kinetics, synthesis of single molecular magnet and chiral materials, nano-catalysis, etc. Issues related to nuclear magnetic resonance are also mentioned, including the protein structure determination, magnetic resonance imaging for medical science, the structure of melt, geosciences and environmental sciences, etc. Moreover, the present condition and achievement of the high magnetic field facility in China are shown in the following part. Three water-cooled magnets have created three world records. The water-cooled magnet WM1 with a 32 mm bore can generate a steady magnetic field of 38.5 Tesla, which has exceeded the previous record 37.5 Tesla. The water-cooled magnet WM5 with a 50 mm bore has produced a magnetic field of 35 Tesla, which is also the highest for the same type of magnets. The water-cooled magnet WM4 with a 32 mm bore has generated a magnetic field of 27.5 Tesla when inputting 10 MW power. All the magnets have corresponding experimental systems. For example, WM1 has a 3He extreme low temperature experiment dewar installed providing a temperature region from 325 mK to 70 K, which is mainly used for transport measurement. The high-homogeneity water-cooled magnet WM2 has a high field high frequency (82 to 690 GHz) electron magnetic resonance continuous wave system installed. WM5 can cooperate with a Fourier transform infrared spectroscopy (18000 to 4000 cm - 1), a vibrating sample magnetometer for magnetization measurement, and a high pressure experiment system (0–200 GPa). The service of the high magnetic field facilities in China will provide strong support for various cutting-edge research and create advantage for significant original achievement.

Achieving a high piezoelectric coefficient (d33) and a high mechanical quality factor (Qm) simultaneously in ferroelectric ceramics has been a persistent challenge, as conventional doping strategies, i.e., donor doping and acceptor doping, inevitably sacrifice one for the other. Here, the inherent trade-off is breaking through a new gradient-acceptor-doping strategy. By judiciously introducing gradient Cu2+-acceptor ions in "soft" (K, Na)NbO3 (KNN) ceramics, a record combination of properties is achieved - a d33 of 350 pC/N and a Qm of 340,-the first co-elevation of both parameters exceeding 300 in KNN-based systems. This represents a fourfold improvement in Qm with only a 10% reduction in d33. Multi-scale structural analysis reveals that the gradient doping retains a "soft" interior for high d33, and creates a "hardened" surface layer that effectively restrains domain switching, accounting for the enhanced Qm. This work offers a new paradigm for designing high-power ferroelectric ceramics by spatially tailoring functional properties.

Recently, the studies on the effects of high magnetic fields on solidification processes have been paid much attention both from the fundamental and applied points of view. With the aid of the enhanced Lorentz force and magnetization effect caused by the remarkably increased magnetic field intensity, several interesting phenomena, such as the control of fluid flow and particle migration in a melt, crystal orientation, and phase alignment, have been obtained. Moreover, the magnetic force induced by the interaction of magnetization and high magnetic field gradient has been evidenced to show significant effects on the microstructure evolution of alloys. In this paper, the recent development of the control of the solidification process by high magnetic fields is reviewed from the view point of uniform magnetic fields and magnetic field gradients.

Cr‐doped ZnO diluted magnetic semiconductor (DMS) nanorods with nominal composition of 1 at.% were synthesized by a hydrothermal method with the assistance of a high pulsed magnetic field (HHPMF). All the Cr‐doped ZnO samples obtained with or without the applied high magnetic field exhibited room‐temperature ferromagnetic behavior. It is observed that the high magnetic field plays an important role in saturation magnetization of the samples. The effects of high magnetic field on the morphology, structure, and magnetic properties of the samples were discussed.

The wall relaxation time for optically pumped 〈Sz〉 polarized sodium atoms colliding with copper, stainless-steel, and dry-film coated surfaces has been measured as a function of an applied magnetic field. Results show that the mean number of wall collisions increases from one to about four before depolarization of sodium atoms occurs on a copper wall in a high (12 kG) magnetic field, whereas the atoms relax after a single collision on a stainless-steel wall even in high fields. The relaxation time for a dry-film coated surface, for the cell geometries used in our work, is dominated by the effusion of polarized sodium atoms from the cell. Our measurements also allow an estimate of the strength of the local magnetic field causing the 〈Sz〉 depolarization and of the correlation time of the depolarization interaction on the surface. The importance of these experimental results as applied to the performance of optically pumped polarized ion sources is also discussed.

High magnetic field is well known to have the function of crystal orientation, which is largely influenced by crystal size and shape to some extent. For crystals with large rod shape, the gravity force functions and affects the crystal orientation. In our experiment, different results were got when a high magnetic field was applied perpendicular and parallel to the gravity force. In this paper, the effect of the gravity force for crystal orientation under the high magnetic field is summarized and compared with the experiment result.

Alignment behavior of the primary Al 3Ni phase in Al–Ni alloy under a high magnetic field

The effect of a high magnetic field applied during oxidation on the structure, optical transmittance, resistivity, and magnetism of cobalt (Co)-doped zinc oxide (ZnO) thin films prepared by oxidizing evaporated Zn/Co bilayer thin films in open air was studied. The relationship between the structure and properties of films oxidized with and without an applied magnetic field was analyzed. The results show that the high magnetic field obviously changed the structure and properties of the Co-doped ZnO films. The Lorentz force of the high magnetic field suppressed the oxidation growth on nanowhiskers. As a result, ZnO nanowires were formed without a magnetic field, whereas polyhedral particles formed under a 6 T magnetic field. This morphology variation from dendrite to polyhedron caused the transmittance below 1,200 nm of the film oxidized under a magnetic field of 6 T to be much lower than that of the film oxidized without a magnetic field. X-ray photoemission spectroscopy indicated that the high magnetic field suppressed Co substitution in the ZnO lattice, increased the concentration of oxygen vacancies, and changed the chemical state of Co. The increased concentration of oxygen vacancies affected the temperature dependence of the resistivity of the film oxidized under a magnetic field of 6 T compared with that of the film oxidized without a magnetic field. The changes of oxygen vacancy concentration and Co state caused by the application of the high magnetic field also increase the ferromagnetism of the film at room temperature. All of these results indicate that a high magnetic field is an effective tool to modify the structure and properties of ZnO thin films.

Monte Carlo investigation of diluted antiferromagnets in high magnetic fields

The effect of a high pulsed magnetic field on the tensile properties and microstructure of 7055 alloy were investigated. In the tensile properties test, the pulsed magnetic field was applied to improve the tensile strength and elongation via the magnetoplasticity effect. The results show that when the magnetic induction intensity (B) is 3 T, the tensile strength and elongation arrives at the maximum synchronously, which has been enhanced by 7.9% and 20% compared to the relevant 576.5 MPa (σb), 7.5% (δ) of the initial sample without magnetic field treatment. The high magnetic field takes effect by altering the spin state of free electrons stimulated between the dislocations and obstacles; afterwards, the structural state of the radical pair is converted from the singlet state with high bonding energy to the triplet state with low bonding energy. Under this condition, the dislocation mobility is enhanced and it becomes easier for a dislocation to surmount the obstacles. The residual stress in the sample is connected closely with the long distance stress generated from the dislocation behavior. At 3 T, the residual stress arrived at the minimum of 16 MPa. Moreover, in the presence of a magnetic field, the common η (MgZn2) in the grain boundary dissolved and moved to internal grains because of the concentration difference, which helped to enhance the tensile strength and toughness of the materials. Finally, the fracture morphology was analyzed by scanning electronic microscopy. The fracture characteristic matches with the plasticity property.

A set of hydrodynamic equations has been applied to processes occurring in non-conductive fluids placed into magnetic fields. The equations are valid for equilibrium magnetization within the framework of a continuous medium. The ranges of physical parameters have been evaluated for which magnetization of a fluid should be taken into account in problems concerning the determination of equilibrium forms, and flows and their stability. The conclusion has been drawn that magnetization of natural fluids in these problems must be taken into consideration for fluids in high (exceeding 1 T) magnetic fields. As examples, the solutions of several typical problems concerning the equilibrium surface of capillary fluids and their stability in external magnetic fields have been considered. Hydrodynamic effects related to magnetization of natural capillary fluids in high magnetic fields are studied with due regard for the above solutions. Hydrodynamic effects in para- and diamagnetic fluids have been studied and the common and distinctive features of these effects discussed.

High magnetic fields have been of interest for some time in solid-state physics. Recent spectroscopic experiments on highly excited barium atoms and the discovery of very large magnetic fields in white dwarf stars and neutron stars have stimulated renewed interest in the spectroscopy of free atoms in high magnetic fields. The various spectroscopic regimes ranging from the low-field Zeeman effect to the high-field Landau regime are reviewed. Calculations of the energy levels of hydrogen, helium and their isoelectronic ions in fields of any strength are surveyed. Observations of the quadratic Zeeman effect in the alkalis and high-field effects in the neutral barium spectrum are described. Finally, recent discoveries of continuum polarization in white dwarf stars, its interpretation in terms of the presence of high magnetic fields, the confirmation of such fields spectroscopically, and some remaining mysteries in these remarkable stellar spectra are reviewed.