Huang Rongxia

Tsinghua University | TH · Department of Physics

This research investigated the effect of Bi4Ti3O12 (BiT) template particles size on the structure and piezoelectric properties of 〈001〉‐textured (Bi0.5Na0.5)TiO3 (BNT)‐based lead‐free piezoelectric ceramics. Results of X‐ray diffractometer analyses and scanning electron microscopy observations showed that high purity BiT template particles could be...

Oxygen vacancy OV plays an important role in a flash sintering (FS) process. In defect engineering, the methods of creating oxygen vacancy defects include doping, heating, and etching, and all of them often have complex processes or equipment. In this study, we used dielectric barrier discharge (DBD) as a new defect engineering technology to increa...

ZrO2 powders of various particle sizes (0.15, 0.7, 500 µm) were used to simulate loose powder bed sintering to prepare BF–BT piezoelectric ceramics. The phase structure, dielectric properties, ferroelectric properties, and piezoelectric properties were compared with the samples sintered by the conventional powder bed method (i.e., powder of the sam...

In this study, we reported that flash sintering (FS) could be efficiently triggered at room temperature (25 ℃) by manipulating the oxygen concentration within ZnO powders via a versatile defect engineering strategy, fully demonstrating a promising method for the repaid prototyping of ceramics. With a low concentration of oxygen defects, FS was only...

The structural, piezoelectric, ferroelectric, and dielectric properties of Mn-modified 0.7Bi1.02FeO3-0.3BaTiO3 (0.7BF-0.3BT) lead-free piezoceramics prepared by direct reaction sintering (DRS) and conventional process (CP) were investigated in present study, respectively. Experimental analysis showed that the addition of small amounts of Mn⁴⁺ ions...

Tristructural-isotropic (TRISO) fuel particles have long been widely used in high temperature gas-cooled reactors (HTGR), where their high temperature mechanical integrity and ability to retain fission products even in the accident conditions are the critical safety issues. In the present work, TRISO particles were subjected to ultra-high temperatu...

In this paper, ZnO was used as a sintering aid as well as reactant in the reactive flash sintering (RFS) of zinc-containing ceramic materials at room temperature (25 °C). The RFS of ZnO-based ceramics, both ZnAl2O4 and Zn2TiO4, were achieved with the application of a high electric field. Contrary to previous reports, the RFS of ZnAl2O4 was divided...

This is the first study to conduct the flash sintering of 3 mol% yttria-stabilized zirconia (3YSZ) ceramics at room temperature (25 ℃) under a strong electric field, larger than 1 kV/cm. At the standard atmospheric pressure (101 kPa), the probability of successful sintering is approximately half of that at low atmospheric pressure, lower than 80 kP...

A new processing method is introduced to prepare large sized FCM fuel with highly ordered arrangement of tristructural isotropic (TRISO) coated particles. Single-layer FCM fuel with SiC as matrix is fabricated by tape casting, and the tapes are then vertically stacked. After sintering, multilayer structured FCM fuel pellets with TRISO coated partic...

Abstract The development of ultra‐high voltage transmission lines requires a ZnO arrester with excellent electrical response and high voltage gradient. Compared with conventional preparation methods, flash sintering allows fast production of novel high‐performance ZnO varistor ceramics with low energy consumption and controlled grain growth. Herein...

This research explored the influence of Nb⁵⁺ doping on the electrical properties and microstructure of [0.852(Bi0.5Na0.5)-0.11(Bi0.5K0.5)-0.038Ba]Ti(1-x)NbxO3 (designated as BNKT-BT). The BNKT-BT samples were fabricated and the XRD results showed that the doping of Nb⁵⁺ ions induced a transformation from the coexistence of both rhombohedral and tet...

Flash sintering of zinc oxide (ZnO) ceramics can be induced at room temperature (25 °C) by electrical breakdown at high electric field strength. However, a strong discharge may degrade the sample. This study investigated the effects of atmospheric pressure and composition on the onset electric field for the flash sintering of ZnO. The experimental...

A series of HfO2-modified (Bi0.475Na0.405K0.055Li0.015)0.95Ba0.05Ti(1-x)HfxO3 (x = 0–0.015) lead-free ceramics were prepared. Results of detailed characterizations showed that the addition of HfO2 had little influence on the grain size, and all of the samples showed the pure perovskite structure. As the Hf⁴⁺ content increases, the samples changed f...

‘Thermal runaway’ was the most popular mechanism in flash sintering, but this theory was inappropriate under high electric field. In this paper, we described electric discharge and breakdown phenomena in experiment to verify this point. And water moisture was found an important role in conducting electric discharge, that increasing moisture content...

Flash sintering is a fabulous method to sinter ceramics in several seconds at low furnace temperatures.For the first report, with an optimized design of electrodes by introducing extra tips, dry zinc oxide specimens were sintered at room temperature under an Alternating Current (AC) field of 1,765 V/cm without any aids. The sintering processes coul...

In this study, plate-like Na0.5Bi0.5TiO3 (BNT) templates with perovskite structure were obtained by two-step molten salt synthesis (MSS) method at a low temperature. Firstly, Bi4Ti3O12 precursors were synthesized at 1030 °C in NaCl–KCl molten salt. Secondly, plate-like Na0.5Bi0.5TiO3 particles with perovskite structure were obtained from plate-like...

The required onset flash sintering temperature of a ZnO ceramic was decreased to as low as room temperature under an applied Alternating Current (AC) field of 3530 V/cm, and the ZnO ceramic achieved 99% of its theoretical density in 40 s without sintering aids. Due to electrical breakdown, flash sintering occurred once the AC field increased to 5 k...

We examined the flash sintering behavior of zinc oxide nanopowder at an onset furnace temperature as low as 50 °C without sintering aids under an AC electric field up to 2800 V/cm. As the electric field applied in the specimens increased and the flash sintering occurred in air, the onset furnace temperature decreased from 190 to 126 °C, while with...

The sintering additive 0.4ZnO-0.6B2O3 (abbreviated as ZnB) was proposed to improve the sintering behavior of (K,Na)NbO3 ceramics. The influence of ZnB on the microstructure and electrical properties of (K,Na)NbO3 ceramics was carefully investigated in detail. Results demonstrated that during the sintering process a liquid phase can form at a relati...

The (Ba0.94Ca0.06)(Ti0.9Sn0.1)O3 (BCTS) ceramics with pure perovskite structure were prepared by conventional solid-state reaction route with the addition of 0–0.8 mol% MnO2. The crystal structure, microstructure, and electric properties were investigated systematically. X-ray diffraction patterns showed that the addition of MnO2 changed the ratio...

The ions doping engineering has already been proved to be an effective approach of adjusting the intrinsic properties of perovskite structured materials and even realizing some new functionality. The polymorphic phase transition effect was put forward to elucidate the enhanced ferroelectric and piezoelectric properties in (K,Na)NbO3-based materials...

Water can trigger flash sintering of ZnO powder pellets at room temperature to achieve ~ 98% of the theoretical density in 30 s without any external furnace heating. The specimen conductivity can be increased by > 10,000 times via absorbing water vapor to enable the room-temperature flash. The initial electric field must be higher than a critical t...

Two-step flash sintering (TSFS) was proposed as a new ceramic fabrication method to achieve fast densification with suppressed grain growth. Using ZnO as an examplar, ~ 96.5% of theoretical density was achieved using TSFS with a grain size of ~ 370 nm, representing a > 3 times reduction of the grain size in comparison with conventional (one-step) f...

Advanced silicon nitride (Si3N4) ceramics were fabricated using a mixture of Si3N4 and silicon (Si) powders via conventional processing and sintering method. These Si3N4 ceramics with sintering additives of ZrO2 + Gd2O3 + MgO were sintered at 1800 °C and 0.1 MPa in N2 atmosphere for 2 h. The effects of added Si content on density, phases, microstru...

Polishing porcelain tile residues (PPR) have accumulated to millions of tons and increases every year. It has become important to recycle the PPR due to the economic gains and environmental sustainability of doing so. However, its direct recycling in the production of porcelain tile has been limited by the fact that SiC particles oxidise during sin...

Lead-free (K0.49Na0.51)(Nb1-xSbx)O3 piezoelectric ceramics were prepared via the conventional sintering method and the effect of the substitution of Nb with Sb on the phase structure, microstructure and electrical properties of the prepared (K0.49Na0.51)(Nb1-xSbx)O3 ceramics was systematically investigated. The prepared ceramics exhibited a single-...

Reactive template grain growth (RTGG) method was applied to prepare <001> grain oriented 0.94(Na0.52K0.48)NbO3-0.06LiNbO3 ceramics using plate-like NaNbO3 particles as template. A two-step sintering procedure was put forward to obtain textured ceramics with electromechanical coupling factor kp=64%, piezoelectric constant d33=220 pC/N and in practic...

Alumina ceramic is a high performance engineering material with excellent properties, including high melting point, high hardness and brittle nature make the alumina ceramic difficult to machine and needing high cost by using conventional manufacturing methods. Coating is an important method for alumina fabrication. The excellent properties of coat...

In the fabrication of YBa2Cu3O7-δ (YBCO) high-temperature superconducting films using a metal organic deposition (MOD) method, the formation of a/b-axis-orientated grains was a common detrimental factor. In this study, Pb addition was utilized to modify the MOD process, and significant improvements of YBCO film's properties were observed. Using the...

Cerium dioxide (CeO2) cap layers for high temperature superconducting coated conductors were fabricated on yttria-stabilized zirconia (YSZ) single crystal substrates via the unbalanced radio frequency (RF) magnetron sputtering method. YBa2Cu3O7–δ (YBCO) films were epitaxially deposited on the as-grown CeO2/YSZ (001) stacks using water-free metal or...

In this study, MgO thin films were deposited by radio-frequency magnetron sputtering. The film thickness in the deposition area directly facing the target center obviously decreased compared with that in other areas. This reduction in thickness could be attributed to the resputtering effect resulting from bombardment by energetic particles mainly c...

Pb addition was used to improve the nucleation and growth of YBa2Cu3O7-δ (YBCO) superconducting films fabricated via the metal organic deposition (MOD) process. By adding lead (II) acetate trihydrate, uniform and stable Pb-containing precursor solution could be obtained. And the final YBCO superconducting films were fabricated through the coating a...

In previously reported low-fluorine MOD-YBCO studies, the lowest F/Ba mole ratio of the precursor solution was 4.5. Further lowering the F/Ba ratio would bring benefits for the environment, thick film deposition, and an understanding of the heat treatment process. On the other hand, the F/Ba ratio must be at least 2 for full conversion of the Ba-pr...

Cerium dioxide (CeO2) films were fabricated on yttria-stabilized zirconia (YSZ) single crystals using unbalanced radio frequency (RF) magnetron sputtering. X-ray diffraction measurements revealed film strain discrepancies under different deposition parameters. Strain evolution was induced by varying sputtering pressure, RF power, and sputtering gas...

The influence of sintering temperature and poling processing on the room temperature phase structure and piezoelectric properties of Li-0.058(Na0.51K0.49)(0.942)NbO3 ceramics were systematically investigated. An approach was proposed to roughly determine the ratio of tetragonal and orthorhombic phase in the as-sintered samples. The result of temper...

Li-0.05(Na0.51K0.49)(0.95)(Nb0.95Ta0.05)O-3 (abbreviated as KNNLT) with addition of La2O3, CeO2, respectively, were prepared by a conventional ceramic fabrication technique. X-ray diffraction pattern shows that the coexistence of orthorhombic and tetragonal phase structure for KNNLT was not changed by adding La2O3 or CeO2. SEM observation indicates...

The oxygen content is one key factor to determine the properties of YBa2Cu3O6+y (YBCO) high temperature superconductors. In this study, YBCO thin films were produced by TFA-MOD method. The oxygenation process was carried out at 450 degrees C for 40 min, in various oxygen partial pressures from 0.01 to 1 atm. An in situ resistance measurement system...

In the present work, lead-free K0.48Na0.52NbO3 (KNN) ceramics were synthesized by conventional ceramics processes. The excess 3.3 mol% Na2CO3 and 1.1 mol% K2CO3 were added to decrease the sintering temperature to 990 degrees C and effectively promote the densification of KNN ceramics. X-ray diffraction results indicated that the excess Na2CO3 and K...

During the fabrication of YBa 2 Cu 3 O 7−δ (YBCO) thin films via the metal organic deposition (MOD) method, the water content of the precursor solution should be reduced to prevent precipitation and other detriment. In most of the reported MOD-YBCO studies, water was used as a solvent, and vacuum distillation was utilized to reduce the water conten...

A novel approach to prepare dense AlN ceramics with high thermal conductivity was proposed. The aluminum isopropoxide (AIP) was introduced to prepare dense AlN ceramics possessing enhanced thermal conductivity via in situ reaction. The effect of AIP and sintering temperatures on the microstructure and properties of AlN ceramics were investigated. R...

0.94(Na0.52K0.48)NbO3-0.06LiNbO(3) with excessive addition of 1.5 mol% Na2CO3 and 1 mol% CuO was synthesized via the traditional solid state reaction. The microstructure, the crystal structure of the abnormal growth grains and the small grains, and the composition of the grains and the liquid phase were thoroughly investigated. The result indicates...

Trifluoroacetate metal–organic deposition (TFA-MOD) is a promising technique to fabricate YBa2Cu3O7−δ (YBCO) superconducting films. However, its slow pyrolysis process, which usually takes more than 10 h, constitutes a barrier for industrial production. In this study, polyethylene glycol (PEG) was utilized to reduce the stress generation inside the...

Ion beam assisted deposition (IBAD) is an important technique to fabricate the second generation high temperature superconducting (2G HTS) wires. Among the fabrication routes of 2G HTS long wires, IBAD route achieved the best performance in recent years. IBAD was adopted in this field in 1991 to obtain biaxially textured buffer layers, which helped...

In this paper, lead-free (Na0.474K0.474Li0.052)(Nb0.948Sb0.052)O3 ceramics were synthesized by a conventional solid-state reaction route. The effects of sintering temperature on the crystal structure, microstructure, densification, dielectric properties, and ferroelectric properties of the KNNLS ceramics were addressed. X-ray diffraction patterns a...

In present work, a simple and direct method was proposed, which could be applied for quantitatively calculating the percentage of 90 degrees domain reorientation in the tetragonal phase of KNNLN ceramics. The relationship between 90 degrees domain reorientation and poling field was established through the X-ray diffraction analysis. Experimental re...

Zr doped Ba0.6Sr0.4TiO3 ceramic was sintered by spark plasma sintering (SPS) and thermal treatment. Sintering behavior, microstructure and dielectric properties of the BST ceramics were investigated by XRD, SEM and impedance analyzer. High dense Ba0.6Sr0.4(Zr0.2Ti0.8)O-3 ceramic with 98.2% of the theoretical density was fabricated at 1270 degrees C...

In the present work, the dependence of microstructure and electrical properties on B-site non-stoichiometry (excess) for (Na0.474K0.474Li0.052)(Nb0.948Sb0.052)O3 − xTa2O5 (KNLNSTx) was symmetrically investigated. The phase structure was pure perovskite when x < 0.02 mol. While x > 0.02 mol, a secondary phase would be found in the samples. The resul...

The phase structure of lead-free Li-0.058(Na0.51K0.49)(0.942)NbO3 (KNNLN) ceramics can be affected by the stress as well as the external electric field. A high piezoelectric constant was obtained in KNNLN ceramics by adjusting the cooling-down speed of the sintering. The {200} reflection X-ray diffraction lines were measured to accurately identify...

In this study, Fe2O3 and TiO2 codoped Li0.05(Na0.5K0.5)0.95(Nb0.975Sb0.025)O3[(1−x) Li0.05(Na0.5K0.5)0.95(Nb0.975Sb0.025)O3–x(Fe2O3–2TiO2) (x=0–0.008)] ceramics were prepared by conventional solid state reaction method, and the microstructure and electrical properties of these samples were investigated. The X-ray diffraction and Raman scattering re...

The effects of sintering temperature and the addition of CuO on the microstructure and piezoelectric properties of 0.95(K0.5Na0.5)NbO3–0.05Li(Nb0.5Sb0.5)O3 were investigated. The KNN-5LNS ceramics doped with CuO were well sintered even at 940°C. A small amount of Cu2+ was incorporated into the KNN-5LNS matrix ceramics and XRD patterns suggested tha...

Iron oxide particles with various shapes, sizes and phase concentrations (including α-Fe2O3 and Fe3O4) have been synthesized through a simple hydrothermal method in the ethylene glycol (EG)-water system. In the preparation conditions, ferric chloride (FeCl3·6H2O) was used as the iron source in the presence of sodium hydroxide (NaOH) without any sur...

Lead-free K0.5Na0.5NbO3-xwt% (0.4ZnO-0.6B(2)O(3)) ceramics were synthesized by conventional ceramics process. The co-doping of ZnO and B2O3 can decrease the sintering temperature of K0.5Na0.5NbO3 ceramics to 1000 degrees C, and the samples show high relative density around 96%. X-ray diffraction (XRD) reveals that Co-doping of ZnO and B2O3 induces...

(1-x) (K0.475Na0.475Li0.05)(Nb0.975Sb0.025)O-3-xmolBiFeO(3) (x=0, 0.002, 0.004, 0.006, 0.008) doped with 0.8mol%CuO lead-free piezoelectric ceramics were prepared by the solid state reaction technique. X-ray diffraction patterns suggested that all the ceramics presented perovskite structure. The compositional dependence of the phase structure and t...

Lead-free K0.5Na0.5NbO3-xmol% FeTiO3 ceramics were synthesized by conventional solid process. The effects of FeTiO3 (FT) addition on the piezonelectric and dielectric properties of K0.5Na0.5NbO3(KNN) ceramics were investigated. Results show that the sintering temperature of KNN ceramics is decreased to 1000 degrees C by adding of more than 0.4 mol%...

(NaxKy) (Nb0.885Sb0.08)-0.035LiTaO(3) lead-free piezoelectric ceramics (NxKyNS-LT) with an excessive amount of Na or K were synthesized by conventional solid-state processes. Effects of Na/K ratio on structure and electrical properties of NxKyNS-LT ceramics were investigated. Excessive Na or K did not change the major crystal structure and barely i...

Flower-like K2Ti6O13 Nanostructure was synthesized via a hydrothermal method using Tetrabutyl Titanate [Ti(OC4H9)(4)] as the Titanium source and KOH as the Potassium source. Reaction conditions were controlled at 200 degrees C for 10 h in the mixed solution of H2O and ethylene glycol. The crystal structure, chemical composition and microstructure o...

Lead-free piezoelectric ceramics 0.95(K0.5Na0.5)NbO3-0.05Li(Nb0.5S0.5)O-3 (KNN-5LNS) were synthesized by the conventional ceramic sintering technique. The phase structure, microstructure and electrical properties of KNN-5LNS ceramics were investigated. The results of XRD indicate that KNN-5LNS possess a pure tetragonal structure. With the sintering...

Lead-free (K0.462Na0.48Li0.058)1+xNbO3(0 ≤ x ≤ 0.03) ceramics with excessive alkaline elements were synthesized by conventional ceramics processes as functions of sintering temperatures and quantities of excess alkaline elements. X-ray diffraction results reveal a transformation from tetragonal phase to orthorhombic phase with increasing the conten...

The 0.95(K0.5Na0.5NbO3)–0.05Li(Nb0.5Sb0.5)O3 doped with 0.8 mol% copper oxide (CuO) lead-free piezoelectric ceramics were synthesized by conventional solid-state reaction route. The introduction of CuO could significantly improve the sinterability of 0.95(K0.5Na0.5NbO3)–0.05Li(Nb0.5Sb0.5)O3 ceramics. The grain size of the specimen was considerably...

A general combined hydrothermal and annealing process for the fabrication of ferrite/perovskite oxide core/shell nanostructures was introduced. The coating of a perovskite oxide (ABO(3)) layer on spherical ferrite particles was performed in two steps. A dense and smooth amorphous layer containing B-site ions of the perovskite oxide was coated first...

Uniform magnetic Fe(3)O(4) chains with an average length of 20 mu m built up by tens of self-assembled microspheres have been synthesized via a simple surfactant-free hydrothermal method. A possible "nucleation-growth-connection-crystallization" growth mechanism has been proposed for the formation of the Fe(3)O(4) chains.

Lead-free 0.94(K 0.48 Na 0.535)NbO 3 –0.06LiNbO 3 –xmol%CuO ceramics were synthesized by conventional ceramics processes. The doping of CuO can decrease the sintering temperature to 8901C and effectively promote the densification of 0.94(K 0.48 Na 0.535)NbO 3 –0.06LiNbO 3 ceramics. X-ray diffrac-tion result reveals that doping of CuO induces lattic...

Monodisperse Fe3O4 crystals have been synthesized by a simple hydrothermal method. Reaction conditions are performed in an ethylene glycol (EG)/NaOH system using FeCl3 as the iron source without adding any surfactants. By adjusting the initial molar ratio of NaOH to Fe3+, several morphologies including solid spheres, hollow spheres, spherical chain...

Plate-like Bi5Nb3O15 (B5N3) particles and rectangular KNb5Bi2O16 (KN5B2) particles were synthesized by the molten salt process and topochemical microcrystal conversion (TMC), respectively. The effects of the synthesis parameters on the phase structure and morphology of B5N3 precursor and KN5B2 were investigated. Results indicated that the retro-syn...

(Bi0.5Na0.5)0.93 Ba0.07TiO3 piezoelectric ceramics doped with In2O3 were studied. X-ray diffraction patterns showed that BNBT ceramics doped with proper amount of In2O3 exhibited a single phase of perovskite structure. The patterns also revealed that the amount of rhombohedral phases decreased and the amount of tetragonal phases increased in the mo...

Lead-free (Bi0.5Na0.5)(0.93)Ba0.07TiO3-x wt %In2O3 ceramics synthesized by direct reaction sintering have been studied. X-ray diffraction reveals that all (Bi0.5Na0.5)(0.93)Ba0.07TiO3-x wt %In2O3 ceramics are of a perovskite structure with coexistence of rhombohedral and tetragonal phases. It is found that the direct reaction sintering promotes gro...

The piezoelectric properties and microstructure of lead-free (Bi0.5Na0.5)1-xBax TiO3 piezoelectric ceramics by direct reaction sintering method were studied. The results show that the content of tetragonal phase is increasing in BNBT ceramics by direct reaction sintering method but still exhibiting a single phase of perovskite structure. There are...

Lead-free (Bi{sub 0.5}Na{sub 0.5}){sub 0.93}Ba{sub 0.07}TiOâ-x wt %InâOâ ceramics synthesized by direct reaction sintering have been studied. X-ray diffraction reveals that all (Bi{sub 0.5}Na{sub 0.5}){sub 0.93}Ba{sub 0.07}TiOâ-x wt %InâOâ ceramics are of a perovskite structure with coexistence of rhombohedral and tetragonal phases. It is found tha...