In the present perspective, evolution of ferroelectric transition and dielectric properties in tungsten bronze oxides is surveyed, and the physical image of modulation structure is established to interpret the variation of ferroelectric transition and macro ferroelectric properties. Different A site cations lead to different modulation structure, and the relationship between temperatures of modulation structure change and ferroelectric transition dominates the crossover from normal to relaxor ferroelectric in tungsten bronze oxides. At low temperature, modulation structure will lock into a regular space group, while the interactions between modulation structure and ferroelectric order results in the low temperature dielectric relaxations.

Bone defects caused by trauma, bone tumor resection, traffic accidents, etc. increase the demand for bone scaffolds and additive manufacturing technology is gradually being widely used in the preparation of bone scaffolds. Three lattice-structured hydroxyapatite (Ca₁₀(PO₄)₆OH₂), HA ceramic green body such as Diamond structure, Rhombic dodecahedron structure and Octet truss structure were manufactured by Digital Light Processing technology and then successfully sintered three kinds of lattice structure HA ceramic scaffolds with a porosity of 70%, and the minimum pore size after sintering is about 200-300 μm. After being sintered at 1 300℃, the HA ceramic is partially decomposed into β-Ca₃(PO₄)₂, and the ceramic grains are tightly bound. Mechanical strength simulation matches actual results, the average compressive strength of the Octet truss structure is the largest, which is 3.16 MPa. In vitro cell experiments showed that the surface of the HA ceramic bone scaffold is beneficial to the spread and adhesion of bone mesenchymal stem cells (rBMSCs), and the HA ceramic prepared by DLP has good biocompatibility. Therefore high-precision lattice structure HA ceramic bone scaffold fabricated by DLP technology is expected to be widely used in bone tissue engineering.

The perovskite and perovskite-like microwave dielectric ceramics have some excellent dielectric properties due to their unique crystal structure. They play an important role in microwave communication technology and can be widely used in satellite communications, radar, and civil mobile communication. In this review, we summarized recent work on the microwave dielectric properties of perovskite and perovskite-like microwave dielectric ceramics. The crystal structure and microwave dielectric properties of a series of perovskite and perovskite-like compounds were discussed. The effects of ion substitution, combined modification and low-temperature sintering on the dielectric properties of the ceramics were analyzed. Finally, the existing main problems were summarized and the future development direction was prospected.

The microstructure of layer perovskite La_0.9Sr_0.1TiO_3+δ was investigated by high-resolution transmission electron microscopy and high angle annular dark field image analysis. The mechanism of oxygen vacancy on the lattice structure was revealed. Based on the results by X-ray diffraction, the oxygen-difficient environment effect on the lattice structure leads to the change of axial length and volume contraction in the material. The partial atomic plane rearrangement and dislocation caused by oxygen vacancy and continuous lattice distortion are identified based on high-resolution microscopic and Z-contrast atomic images, respectively. The effective regulation of oxygen vacancy defect shows a great significance on changing the microstructure of materials and further preparation of high-performance perovskite materials.

A lead-free piezoelectric ceramic (NaBi)_0.5-x(KCe)_xBi₂Ta₂O₉(NBTO-x, 0≤x≤0.15) was prepared by a solid-state reaction method. The influence of K/Ce ions co-doping content on the structure and electrical properties of NBTO ceramic was investigated. Based on the results by X-ray diffraction, a bismuth layered structure compound with m=2 is formed in all the ceramic samples. The Curie temperature T_C of the samples decreases gradually with the increase of K/Ce ions co-doping content. The piezoelectric properties of the samples are improved due to K/Ce ions co-doping, The piezoelectric constant d₃₃ initially increases and then decreases with the increase of K/Ce ions co-doping content. The ceramic with x of 0.075 exhibits the optimal properties, i.e., d₃₃ of 19.0 pC/N, the Curie temperature T_C of 735℃, dielectric loss tanδ of 0.137%, and volume density ρ of 9.113 g·cm^-3. The piezoelectric constant d₃₃ of NBTO (x of 0.075) ceramic has a good temperature stability, and the d₃₃ of NBTO ceramic annealed at 600℃ for 2 h is still as high as 17.8 pC/N, which is 93.7% of the original value (i.e., d₃₃=19.0 pC/N).

La³⁺-doped Ca_1-xLa_xBi₂Nb₂O₉(CBN-xLa, x=0.00, 0.02, 0.04, 0.06, 0.08, 0.10) piezoceramics were synthesized by a solid-state reaction method. The crystal structure, microstructure, dielectric, piezoelectric and ferroelectric properties as well as high-temperature conductive mechanism of La³⁺-doped CBN ceramics were investigated. The results show that an appropriate amount of La³⁺ donor ion substituted for Ca²⁺ ion can optimize the crystal structure, decrease the grain size, reduce the oxygen vacancy, and effectively improve the electrical properties of CBN ceramics. The Ca_0.92La_0.08Bi₂Nb₂O₉ ceramics with the optimal performance (high piezoelectric coefficient (d₃₃=11.7 pC/N) and the Curie temperature (T_C=905℃), remanent polarization (2P_r=9.51 μC/cm²) and low dielectric loss, (tanδ=3.87% at 550℃)). After annealing, the piezoelectric properties of all the samples remain stable at 800℃. According to the complex impedance plots, the grain boundary and grain both contribute the impedance, and the conduction mechanism is closely related to oxygen vacancies. Moreover, La³⁺-doping can effectively improve the resistivity of CBN ceramics at high temperatures, indicating a potential application in high-temperature sensors.

A gradient structure piezoelectric fiber composite dynamic simulation model for energy harvesting was built using a multiphasics simulation software, and the effects of the interdigitated electrode structure, applied load and piezoelectric active layer parameter on the energy harvesting behavior were studied. The results show that under the same active layer structure parameters, gradient structure piezoelectric fiber composites can obtain larger output voltage than traditional structures. Under the fixed gradient structure parameters, the polymer elastic modulus is smaller, the higher the output voltage. And the output voltage increases first and then decreases as the volume fraction of the piezoelectric fiber increases. The larger the elastic modulus of the polymer, the higher the volume fraction of the piezoelectric fiber when the maximum output voltage is obtained. Reasonable adjustment of the mechanical load frequency and load resistance of the system can effectively enhance the electrical output performance of the energy harvesting model.

Acoustic emission (AE) monitoring tests were carried out on the tensile failure process of plain weave C/SiC composites with different strengths. An unsupervised clustering method, based on the improved genetic algorithm, was used to recognize the characteristics of various AE classes, corresponding to different microscopic fracture mechanisms. Combined with the fracture surface observation, the relationship between tensile strength, damage mechanisms, and the evolution of AE signals was analyzed. It is found that: The AE energy of fiber breakage can reflect the bonding strength of the fiber/matrix interface; For the specimen with the lowest strength, there has the matrix enrichment area leading to the stress concentration, and the matrix cracking events account for more than 50% in the initial stage; For the specimen with the medium strength, the failure of fiber are mainly the breakage of single or a few fibers, due to the strong fiber/matrix interface; For the specimen with the highest strength, the integral breakage of fiber clusters is the dominant failure mode, due to the moderate interface bonding strength.

Oscillatory pressure sintering (OPS) technique was used to prepare silicon nitride ceramics with high quality. In comparison with hot pressure (HP) sintering process, the density, phase, grain size, aspect ratio and microstructure of silicon nitride ceramics by two methods were further investigated. The densification effect of oscillatory pressure on silicon nitride ceramics were studied. The results indicate that the silicon nitride ceramic has reached a complete phase transition from α phase to β phase under OPS process and its relative density has reached 99.82%. The grain sizes of OPS specimen are significantly increased compared with the specimen prepared by HP process. The average aspect ratio of the grains has increased from 3.79 to 4.86 when the fabricated process changed from HP to OPS. Bending strength, hardness and fracture toughness reached 1 333 MPa, 16.2 GPa, 12.1 MPa·m^1/2, respectively. Fracture surface energy also increased with the introduction of oscillatory pressure. In addition, obvious deformation streaks and dislocation movement areas are observed through TEM analysis. Obviously, the application of oscillatory pressure improves the densification rate and the growth driving force of grains. The plastic deformation of silicon nitride during the densification process were also found. Thereby, the sintering densification process was accelerated.

Aerogels are known as the "magic material to change the world in twenty-first century". Because of its unique super porous structure, it has many excellent properties and wide application prospect in many fields. However, the mechanical brittleness and the cumbersome preparation process caused by the network structure of aerogels greatly hamper its widely application, which is a bottleneck problem in the aerogel field. The development status of aerogel materials is reviewed, and several structural strengthening strategies commonly used in aerogels are summarized. The classification and preparation of aerogels and the strategies for optimizing the structure and properties of aerogels are summarized. At the same time, the methods of optimization and enhancement in recent years such as biomimetic reinforcement, concentration induced hardening and microwave sintering are reviewed. Meanwhile, the prospect of aerogel is also forecasted.

The fracture toughness of zirconia toughened alumina (ZTA, 15% ZrO₂ in mass fraction) ceramics was improved via the addition of plate-like Pr_0.833Al_11.833O₁₉ crystals prepared by in-situ solid-state reaction. The effects of Pr₆O₁₁ dopant content and sintering system on the microstructure and mechanical properties of ZTA ceramics were investigated. The results show that the plate-like Pr_0.833Al_11.833O₁₉ crystals can be in-situ prepared at Pr₆O₁₁ doping content of >1.0% (mass fraction) and by heat preservation at 600℃ for 4 h, 800℃ for 1 h and 1 600℃ for 2 h, respectively. The ZTA ceramic with the plate-like crystals at an average aspect ratio of 11.76 uniformly distribute at Al₂O₃ grain boundary has the fracture toughness of 6.37 MPa·m^1/2, which is increased by 88%, compared to the ZTA ceramic without the plate-like crystals.

The secondary pressure assisted flash sintering process of tetragonal zirconia ceramics was developed. The process optimized the process and eliminated the deterioration of microstructure caused by high power flash sintering at critical flash temperature. The results show that: the multi-step pressure assisted flash sintering process retains the advantages of low-temperature and instantaneous sintering, avoids the complex green pressing process and the high cost of precious metal electrode. Yttrium stabilized zirconia can be densified by multiple flash sintering. The sintering temperature is lower than 1 050℃ and the sintering time is less than 200 s. The density of tetragonal zirconia ceramic material prepared by this process is more than 90%.

White light emitting diode (WLED) is considered as a fourth-generation green light source and presents some applications in lighting fields due to its advantages of long service life, high luminous efficiency, and free environmental pollution. The exisiting main commercialization use of WLED is a blue chip combined with YAG:Ce³⁺ phosphor. However, the luminescence performance of the WLED gradually declines with the increase of temperature due to a poor thermal conductivity of the resin encapsulating the phosphor, thus becoming difficult to apply to high-power lighting. It is necessary to obtain the superior phosphor materials with high quality and stability. In recent years, directionally solidified Al₂O₃/YAG:Ce³⁺ eutectic phosphor composite is considered as a novel bulk phosphor material for a high-power WLED lighting, which is expected to substitute conventional phosphors, due to its excellent luminous properties, high temperature strength and thermal stability, low power consumption as well as superior quantum efficiency. This review summarized the main preparation technologies of Al₂O₃/YAG:Ce³⁺ eutectic phosphor composite. Meanwhile, the microstructure, luminescence mechanism, and influential factors of the Al₂O₃/YAG:Ce³⁺ eutectic phosphor composite were analyzed. In addition, the future development direction was also discussed.

Based on the introduction of the dislocation formation and movement mechanism in Czochralski silicon, the effects of seed crystal thermal shock, solid-liquid interface, crystal diameter, and impurities on the dislocations during the crystal growth process were summarized. The effects of boron, germanium, nitrogen, phosphorus, arsenic doping elements and oxygen impurities on the dislocation behavior of the Czochralski silicon were analyzed. The thermal shock of the seed crystal can lead to the dislocations, which can be suppressed by some methods such as necking, melting back, seed crystal preheating, and the use of doped seed crystal. The solid-liquid interface convex to the melt causes a large edge shear stress to produce the edge dislocations. The formation of dislocations can be suppressed when the shape is flat. In heavily n-type doped single crystal silicon, the evolution of solid-liquid interface and the formation of {111} edge surface may promote the generation of supercooling region and interrupt the growth of top cone, thereby causing the dislocations, and the length of the edge surface is related to the curvature of the melting isotherm. Incomplete seeding of the seed crystal will produce the dislocations that cannot be discharged from the crystal, and then extend to the silicon rod. The increase in the diameter of single crystal silicon and the fluctuation of the diameter during the crystal growth process will increase the risk of dislocation formation. Doping is an effective method to inhibit the formation and movement of dislocations. Boron, germanium, nitrogen, phosphorus, arsenic and oxygen impurities all have different degrees of inhibition on the dislocations mainly due to the pinning effect of impurity atoms on the dislocations. Finally, some future research aspects on necking process, thermal field design, doping process and theoretical modeling were prospected.

The micropipe (MP) in silicon carbide (SiC) single crystal substrate is a fatal defect for SiC-based devices, which will seriously affect the yield of SiC power devices. In this paper, the 6 in n-type 4H-SiC single crystals without micropipe defect were prepared by the optimized growth design based on physical vapor transport (PVT) method. The effects of the optimized growth design on the elimination of micropipes were also studied. Based on the principle of crystallography and kinetics, the mechanism of micropipe decomposition and closing is clarified. In summary, the optimized growth design adopted in this paper not only promotes the stability of SiC single crystal growth, but also can improve the crystalline quality of SiC single crystal, and can quickly reduce the density of micropipes. The prepared large size 6 in n-type 4H-SiC single crystals without micropipe defect will be more suitable for making high-voltage and ultra-high-voltage power devices.

After the optimization of temperature field and the process parameters, the NaCl single crystal with the size ofФ130 mm×100 mm was grown by the resistance heating Czochralski (Cz) method and the bottom of the crucible compensation technology. XRD analysis shows that the NaCl crystal is a cubic system with a lattice constant of a=0.564 02 nm. The transmittance test of the crystal suggests that the transmittance of a sample with a thickness of 4 mm is greater than 91.5%. The vickers hardness of the crystal is 21.52 kg/mm², and the hardness coefficient is 1.672, which proves that NaCl crystal is a soft material. The optical uniformity of the crystal decreases with the dislocation density increase. The thermoluminescence luminescence (TL) curve shows that the thermoluminescence peaks of the crystal are located at 74.35 and 221.14℃, respectively, and the luminous intensity of the latter is more than 5 times that of the former. The results show that NaCl crystal is a high-quality material, which can be used in dosimetry and infrared fields.

A series of Cs₂NaBiCl₆:Mn²⁺ double perovskite phosphors were prepared via liquid-phase synthesis, and their structures and luminescent properties were investigated by X-ray diffraction and fluorescence spectroscopy. The result show that with the gradual introduction of Mn²⁺, localized excitations centered on Bi³⁺ ions in the host lattice Cs₂NaBiCl₆ strongly absorb near-UV light, and the energy transfer between Bi³⁺ and Mn²⁺ promotes the electron transition between atomic d orbitals, thus leading to an intense orange-yellow photoluminescence. The photoluminescence reduces when the manganese-bismuth molar ratio is 0.7 due to the concentration quenching effect. Also, a broad emission peak centered at 590 nm is assigned to the ⁴T₁→⁶A₁ transition of octahedrally coordinated Mn²⁺. Based on the excitation spectrum, there are some peaks at 354 nm that arise from 6s²→6s¹6p¹ excitations of Bi³+ions. It is indicated that Cs₂NaBiCl₆:Mn²⁺ could be a promising fluorescent phosphor synthesized without the use of expensive reagents and toxic elements materials.

Tb³⁺ single doped and Tb³⁺/Ce³⁺ co-doped high aluminum blast furnace slag, aluminosilicate luminescent glass was prepared by a high-temperature water-quenching method. The effects of heat treatment and co-doping on the luminous properties of glass were studied. The results show that, after holding at 1 000℃ for 4 h, the glass host crystallizes into Ca₂(Mg_0.5Al_0.5)(Si_1.5Al_0.5O₇), and the luminescence performance drops sharply. The highest luminous intensity of 4%(mole fraction) Tb³⁺ doped luminous glass is about 12 times higher than of that crystallized. With Ce³⁺ ions introduced, energy transfer occurs between Ce³⁺ ions and Tb³⁺ ions due to multipolar interaction, and the luminous intensity of Tb³⁺/Ce³⁺ co-doped luminescent glass reaches nearly 6 times of the Tb³⁺ single doped. 4%Tb³⁺/1%Ce³⁺ co-doped luminescent glass has good luminescence thermal stability at 150℃, and can be used as a green solid-state luminescent material excited by near ultraviolet LED.

The up-conversion (UC) luminescence properties of natural sodalite (Na₈Al₆Si₆O₂₄Cl₂) co-doped with Europium and ytterbium (Eu³⁺ and Yb³⁺, respectively) was studied for the first time under excitation of near infrared reflectance (NIR) light. Cooperative energy transfer process was discussed as the possible mechanism for the visible up-conversion luminescence of Eu³⁺. The crystal structure of fluorescent powder was investigated using an X-ray powder diffraction system. The prepared phosphors radiate very strong red fluorescence with chromaticity coordinates of (0.661, 0.339) at 265 nm excitation, which consists of red light with higher purity at 611 nm due to Eu³⁺ (⁵D₀→⁷F₂), so it can be used as a red phosphor. The photo physics involved in this emission is explained.

Four ternary complexes [Ln₂(PIA)₂(acac)₂] (Ln=Sm (1), Eu (2), Tb (3), Dy (4)) were synthesized with isophthalic acid (H₂PIA, C₈H₆O₄), acetylacetone(Hacac, C₅H₈O₂) and Ln(NO₃)₃·nH₂O in ethanol solution. These complexes were characterized by elemental analysis, infrared (IR) spectra, and thermogravimetric analysis (TG). Their possible structures were proposed. In order to compare the luminescent properties between ternary complexes and corresponding binary complexes, the binary complexes [Ln₂(PIA)₃(H₂O)₄] and Ln(acac)₃(H₂O) (Ln=Sm, Eu, Tb, Dy) were also prepared. The fluorescent spectra of the ternary and binary complexes were determined at room temperature. The results show that all complexes displayed the characteristic emissions of rare earth center ions. The luminescent intensities of the ternary complexes (except the dysprosium complex) were stronger than that of the binary complexes, indicating that the synergistic sensitization effect had occurred for the center ions from the double ligands. These experimental results can be explained by the energy matching of the lowest triplet energy level T₁ of the two ligands (calculated from Gaussian theory) and the lowest excited state energy level of the central metal ions.

A high-flux T-zeolite membrane was prepared with a macromolecular substance with adjustable pore structure-1,2-bistriethoxysilyl ethane abbreviation (BTESE) on the surface of T-zeolite membrane synthesized via crystallization for 5 h. The properties of T-zeolite membrane were characterized by X-ray diffraction, scanning electron microscopy and pervaporation analysis. Meanwhile, the pervaporation performances of the BTESE modified membrane and the secondary crystallization membrane were compared. The results show that the thickness of the membrane modified by BTESE is only a half of the thickness of the secondary crystallization membrane. The flux of the modified BTESE membrane is 4.358 kg·m^-2·h^-1, which is twice greater than that of the secondary crystallization membrane. In addition, the acid resistance test shows that the BTESE modified membrane has a stable pore structure and a good separation performance under weak acid conditions at pH value of >4.

A series of La_0.6Sr_0.4Co_1-yFe_yO_3-δ (LSCF, y=0.2, 0.5 or 0.8) oxides with perovskite structure was prepared by sol-gel method, and then the corresponding hollow fiber membranes with different microstructures were fabricated through the phase inversion/sintering method. The influence of the coagulant and Co/Fe molar ratio on the microstructure and oxygen permeability of LSCF hollow fiber membranes was investigated. LSCF hollow fiber membrane with a dense thin outer surface and large numbers of finger-like channels was prepared by using a mixture of 70% (mass fraction) NMP and 30% ethanol as internal coagulation and deionized water as outer coagulation. The finger-like pores could greatly reduce the diffusion resistance, and thus improving the oxygen permeability. With the increase of temperature and the rate of helium sweeping gas, the oxygen permeation flux of LSCF hollow fiber membrane increases gradually. The Co/Fe molar ratio has an important influence on the membrane microstructure and oxygen permeation. The O₂ permeation flux increased with increasing the Co/Fe molar ratio. The oxygen permeation flux reached up to 2.81 mL·min^-1·cm^-2 at a helium sweeping rate of 120 mL·min^-1 and Co/Fe molar ratio of 4 at 950℃ (the test temperature of oxygen-permeable membrane).

Green synthesis of Mg-Al-CO₃ layered double hydroxides/calcite composite powders (LDH/Cal) via the acid dissolution and co-precipitation process was investigated in this paper. This method uses dolomite as a source of magnesium, calcium, and carbon dioxide with no CO₂ release in the process of preparation. LDH/Cal prepared under optimized conditions (acid dissolution temperature was 60℃, OH^-/[Mg²⁺+Al³⁺] mole ratio was 3.5∶1.0, Mg²⁺/Al³⁺ mole ratio was 3∶1, temperature and time of crystallization were 120℃ and 18 h, respectively) was characterized. LDH/Cal consists of LDH (39.5%) and calcite (60.5%). The calcite was regular and granular with a diameter of about 0.6 to 1.8 μm, and LDH contained well-defined plate-like particles with regular hexagonal shape, and sizes between 100 and 200 nm. The acid dissolution process of dolomite and the compound mechanism of LDH and calcite were discussed.

TiC/SiC coated natural flake graphite was used as a new carbon source of low carbon Al₂O₃-C refractories which was prepared by self-propagating high-temperature synthesis (SHS) using Ti, Si and GF as raw materials. The phase composition of the products was characterized by X-ray diffraction and the microstructure as well as the element distribution were studied via a scanning electron microscopy coupled with an energy dispersive spectroscopy. The effects of the amount of graphite on the reaction were studied. The results show that the maximum amount of GF added is 38.6% (mass fraction) under a self-sustained combustion wave, and a continuous, complete TiC-SiC coating layer with a uniform thickness (about 360 nm) is synthesized on the GF surface. The effects of the amount of the coated graphite on the properties of low carbon Al₂O₃-C refractories were invetigated. The results revel that the Al₂O₃-C refractory shows the optimal properties when 3% (mass fraction) coated graphite is used: the lowest apparent porosity (12.9%), the highest cold modulus of rupture (20.7 MPa), and the thickness of oxide decarburization layer and the erosion depth of slag are reduced by 41.8% and 57.1%, respectively.