关于Maxwell方程在Lorentz变换下的不变性原理

以线性代数为工具，引进张量分析的概念与运算规律，从而对于麦克斯韦尔（Ｍａｘｗｅｌｌ）方程在罗伦兹（Ｌｏｒｅｎｔｚ）变换下的不变性原理，给出了一个简明的证明．     

Martensitic transformation and magnetic properties of aged Ni-Fe-Ga-Ti shape memory alloy

This article reports the effect of ageing on the microstructure, martensitic transformation, magnetic properties, and mechanical properties of Ni51FelsGa27Ti4 shape memory alloy. There are five specimens of this alloy aged at 573 up to 973 K for 3 h per each. This range of ageing temperature greatly affects the microstructure of the alloy. As the ageing temperature increased from 573 up to 973 K, the microstructure of Ni51FelsGa27Ti4 alloy gradually changed from the entirely martensitic matrix at 573 K to the fully austenitic microstructure at 973 K. The volume fraction of precipi- tated Ni3Ti particles increased with the ageing temperature increasing from 573 to 773 K. Further increasing the ageing temperature to 973 K decreased the content of Ni3Ti in the microstructure. The martensitic transformation tempera- ture was decreased steadily by increasing the ageing temperature. The magnetization saturation, remnant magnetization, and coercivity increased with the ageing temperature increasing up to 773 K. A further increase in ageing temperature decreased these raagnetic properties. Moreover, the hardness values were gradually increased at first by increasing the ageing temperature to 773 K, and then dramatically decreased to the lowest value at 973 K.     

The NbO6 octahedral distortion and phase structural transition of Eu3+‐doped K0.5Na0.5NbO3–xLiNbO3 ferroelectric ceramics

A small quantity of Eu³⁺ ions were doped in the lead‐free ferroelectric K_0.5Na_0.5NbO₃–xLiNbO₃ (KNN–xLN, 0 ≤ x ≤ 0.08) ceramics to investigate the NbO₆ octahedral distortion induced by the increasing LN content. In addition, the phase structure, ferroelectric, and photoluminescence properties of K_0.5Na_0.5NbO₃–xLiNbO₃:0.006Eu³⁺ (KNN–xLN:0.006Eu³⁺) lead‐free piezoelectric ceramics were characterized. All the X‐ray diffraction, Raman spectra, dielectric constant vs temperature measurements and the photoluminescence of Eu³⁺ ions demonstrated that the prepared ceramics undergo a polymorphic phase transition (PPT, from orthorhombic to tetragonal phase transformation) with the rising LN content, and the PPT region locates at 0.05 ≤ x ≤ 0.06. The ferroelectric properties, Raman intensity ratios and photoluminescence intensity ratios show similar variations with the increasing LN content, all with a maximum value achieved at the PPT region. We believe that the close relationship among the ferroelectric properties, Raman intensity ratios, and photoluminescence intensity ratios is caused by the NbO₆ octahedral distortion. The photoluminescence of Eu³⁺ ion was discussed basing on the crystal‐symmetry principle and Judd‐Ofelt theory.     

In situ Raman spectroscopy of pressure‐induced phase transformations in polycrystalline TbPO4, DyPO4, and GdxDy(1−x)PO4

Xenotime DyPO₄ and Gd_xDy_(1?x)PO₄ (x = 0.4, 0.5, 0.6) (tetragonal I4₁amd zircon structure) have been studied at ambient temperature under high pressures inside a diamond anvil cell with in situ Raman spectroscopy. The typical Raman‐active modes of the xenotime structure were observed at low pressures and the appearance of new Raman peaks at higher pressures indicated a phase transformation to a lower symmetry structure—likely monoclinic. Raman mode softening was observed, resulting in a line crossing at approximately 7‐8 GPa for each material and preceding the phase transformation. The onset of phase transformation for DyPO₄ occurred at a pressure of 15.3 GPa. DyPO₄ underwent a reversible phase transformation and returned to the xenotime phase after decompression. The transformation pressures of the solid solutions (Gd_xDy_(1?x)PO₄) were in the range 10‐12 GPa. The Gd_xDy_(1?x)PO₄ solid solutions yielded partially reversible phase transformations, retaining some of the high‐pressure phase spectrum while reforming xenotime peaks during decompression. The substitution of Gd into DyPO₄ decreased the transformation pressure relative to pure DyPO₄. The ability to modify the phase transformation pressures of xenotime rare‐earth orthophosphates by chemical variations of solid solutions may provide additional methods to improve the performance of ceramic matrix composites.     

Lead‐free (K,Na)NbO3‐based ceramics with high optical transparency and large energy storage ability

Highly transparent lead‐free (1‐x)K_0.5Na_0.5NbO₃–xSr(Zn_1/3Nb_2/3)O₃ (KNN–xSZN) ferroelectric ceramics have been synthesized via a conventional pressureless sintering method. All samples are optically clear, showing high transmittance in the visible and near‐infrared regions (~70% and ~80% at 0.5 mm of thickness, respectively). This exceptionally good transmittance is due to the pseudo‐cubic phase structure as well as the dense and fine‐grained microstructure. In addition, a high energy storage density of 3.0 J/cm³ has been achieved for the 0.94K_0.5Na_0.5NbO₃–0.06Sr(Zn_1/3Nb_2/3)O₃ ceramics with submicron‐sized grains (~136 nm). The main reason is likely to be the typical relaxor‐like behavior characterized by diffuse phase transition, in addition to the dense and fine‐grained microstructure. This study demonstrates that the 0.94K_0.5Na_0.5NbO₃–0.06Sr(Zn_1/3Nb_2/3)O₃ ceramic is a promising candidate of lead‐free transparent ferroelectric ceramics for new areas beyond transparent electronic device applications.     

Phase evolution and chemical durability of Zr1‐xCexO2 (0 ≤ x ≤ 1) ceramics

Ce‐doped zirconia ceramics with general stoichiometry of Zr_1‐xCe_xO₂ (0 ≤ x ≤ 1) have been obtained by substitution of Ce⁴⁺ for Zr⁴⁺ in ZrO₂. The phase and microstructure evolutions of the ceramics were investigated, and the effects of composition, temperature, and pH value on the chemical durability of the ceramics were also studied. The results show that the phase transformation from monoclinic to tetragonal takes place at about x = 0.2, and from tetragonal to cubic at about x = 0.6. It is found that the increase in Ce content and/or sinter temperature promote the phase transformation. The leaching studies show that the normalized leaching rates of Ce (LR_Ce) increase with increasing Ce content. Moreover, LR_Ce in acid solution are higher than those in neutral and alkaline solution. After 42 days, LR_Ce is 10^?5 ~ 10^?7 g m^?2 d^?1 under all different leaching conditions, exhibiting their excellent chemical durability.     

Structure,electrical, and thermal expansion properties of PZnTe–PZT ternary system piezoelectric ceramics

xPb(Zn_0.5Te_0.5)O₃–(1?x)Pb(Zr_0.5Ti_0.5)O₃ (PZnTe–PZT) ceramics were prepared by the solid‐state reaction method. The phase structure, microstructure, ferroelectric and dielectric properties and thermal expansion properties were systematically investigated. X‐ray diffraction analysis showed the morphotropic phase boundary (MPB) existed at the composition of x = 0.08, which was the coexistence of the rhombohedral phase and the tetragonal phase. The grain size of ceramics decreased rapidly from 10‐20 μm to 1‐3 μm when the PZnTe was added in. The PZnTe–PZT ceramics at the MPB composition showed the largest high field effective piezoelectric coefficient and the lowest strain hysteresis H. The dielectric permittivity and phase transition temperature exhibited strongly compositional dependence. A good linear relation was shown in T_m temperature vs x content and a DPT behavior was found in xPZnTe–(1?x)PZT (x = 0.02‐0.08). The thermal expansion properties showed a low thermal expansion coefficient in the low temperature while a high thermal expansion coefficient in the high temperature. Besides, the thermal expansion curve also showed the characteristic of DPT in PZnTe–PZT ceramics.     

裂解炉的综合节能措施

介绍了裂解炉通过工艺优化、精心操作来实现经济模式运行;通过加强管理维护、延长设备使用寿命来降低设备更新成本;通过采用新技术、技术改造来回收能量,减少直接能量损失,达到节能降耗、综合节能的目的。     

High-entropy,phase-constrained,lanthanide sesquioxide

Oxides can experience structural transformations resulting from variations in cation oxidation states or coordination geometry upon thermal treatment. Whether such structural distortions can affect the stability of high-entropy oxides has not been studied. In this research, a new, high-entropy, lanthanide sesquioxide, Gd_0.4Tb_0.4Dy_0.4Ho_0.4Er_0.4O₃ solid solution having a single phase, cubic-bixbyite structure was synthesized, with no phase transformation from room temperature to 1650°C. The phase stability was examined via both in situ and ex situ, high-temperature, synchrotron, X-ray powder diffraction. This high-entropy oxide could inhibit the phase transformations occurring in constituent monocation sesquioxides, Tb₂O₃ and Gd₂O₃, via random arrangement of multications.     

A critical phenomenon of phase transition in hydroxyapatite investigated by thermally stimulated depolarization currents

We observed a critical phenomenon of ferroelectric transition in hydroxyapatite (HAp) through measuring the thermally stimulated depolarization current of polycrystalline monoclinic HAp. Two peaks attributable to hydroxide (OH^?) ion dipole reorientations were observed. The one was very sharp, the other displayed a broad peak ranging from 350 to 550 K. While the broad peak can be attributed to the diffusive reorientation motions of OH^? ion dipoles, the sharp peak, related to the ferroelectric phase transition, implies the presence of ferroelectricity in HAp. The sharp peak was found near 380 K, the phase‐transition temperature from the monoclinic to hexagonal is ascribed to a critical phenomenon caused by the ferroelectric behavior of OH^? ion dipole reorientations.