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The stability of AlON powder in the aqueous system was studied during the gel-casting procedure of AlON ceramic. The pH value of AlON slurry, the phase assemblage and the morphology of AlON powder all suggested the excellent stability of untreated AlON powder even in hot water. Finally, highly-transparent AlON ceramic pellets (D = 110 mm and D = 22 mm) were fabricated by a feasible and easy aqueous gel-casting method. The polished AlON ceramics with 3.5 mm thickness possesses the highest inline transmittance above 86% at the wavelength of 2000 nm.

The development of novel tritium breeding materials was urgently needed in order to continuously optimize the tritium breeding ratio (TBR) of thermonuclear fusion reactors. From this point of view, Li4TiO4-Li2TiO3 core-shell breeding materials with more reasonable structure and theoretical Li density of 0.464 g/cm3 were prepared in this work. Notably, the mass transfer experiment at 900 °C in 1% H2/Ar shows that the theoretical Li density of this core-shell material after heating for 30 days was significantly higher than that of other breeding materials, indicating that it can provide more stable and efficient TBR. Specifically, the Li mass loss of the sample after 30 days heating was 3.4%, resulting in a decrease of Li density to 0.415 g/cm3. The mechanism of Li mass loss in Li4TiO4-Li2TiO3 core-shell breeding materials was investigated in detail. Moreover, the samples did not crack or collapse during the long-term heating process, and always maintained a satisfactory crushing load, revealing that this core-shell breeding ceramic can be used for a long time under severe operating conditions.

Cubic polycrystalline LiAlON solid solution ceramics with differential transparencies were prepared by solid-state reaction sintering and post-HIP. The light transmission properties of the ceramics were studied via in-line transmittance (IT) and real in-line transmittance (RIT) measurements. The main scattering resources were characterized via SEM and EDS analysis. It was suggested that, composition inhomogeneity in the solid solution could contribute to strong light scattering with low RIT even though the IT is very high. LiAlON ceramic with high transparency (RIT up to 85.5%) was mainly benefited from the eliminations of composition inhomogeneity and residual pores.

A comparative study between the microwave and conventional sintering of Li2TiO3–Li4SiO4 biphasic ceramic pebbles was systematically performed. Comparing to samples sintered by conventional method, the microwave sintered samples exhibited homogeneous microstructure with uniform grain size distribution. In addition, the microwave sintered samples showed higher relative density (86.0% T.D.) and crush load (22.7 N). The results indicated that the microwave sintering process is a prospective method for fabricating Li2TiO3–Li4SiO4 biphasic ceramic pebbles with excellent mechanical performance as tritium breeder materials.

Lithium metatitanate (Li2TiO3) ceramic pebbles were fabricated from the powder synthesised via low-temperature solid-state precursor method. Solid H2TiO3 and LiOH·H2O react chemically during ball milling process to form a nano-sized precursor powder. Pure β-Li2TiO3 powder can be obtained by calcining the precursor powder at 500 °C, which is half the temperature of conventional solid-state method. The synthesis process is simple and low-cost, which would be more available to achieve batch production among all feasible techniques. The low-temperature calcination will effectively avoid hard particle aggregates and poor sinterability caused by high-temperature heat treatment, which is conducive to prepare ceramics with good properties. The results show that the powder exhibits high sinterability with small particle size of 19 nm. The Li2TiO3 ceramic pebbles sintered at 800 °C have small grain size (470 nm), high relative density (83%) and good crush load (45 N), which has great potential as tritium breeding materials for fusion reactors.

An advanced core-shell ceramic pebble with Li4TiO4 pure phase core and Li2TiO3 nanostructured shell was prepared by a physical coating method. The phase compositions, morphology and microstructure of Li4TiO4–Li2TiO3 core-shell ceramic pebbles were investigated. We discovered that using chitosan solution to assist rolling coating helps to improve the coating uniformity of core-shell green pebbles. In addition, the results show that the obtained Li4TiO4–Li2TiO3 core-shell ceramic pebbles have a diameter of ∼1.1 mm, the shell thickness of ∼13 μm and density of 2.31 ± 0.03 g/cm3. It is also noted that the Li2TiO3 shell still maintains the nanostructure (∼80 nm) after sintering. This study provides a feasible method for preparing Li4TiO4–Li2TiO3 core-shell ceramic pebbles which have a great potential application for the test blanket module (TBM) of International Thermonuclear Experimental Reactor (ITER).

In this study, Li 2 O porous ceramic pebbles were synthesized by decomposing the xLi 2 CO 3 -yLiNO 3 precursor pebbles at low temperature. This efficient decomposition reaction was mainly attributed to the two-stage support decomposition of Li 2 CO 3 and LiNO 3 . The results indicated that the molar ratio of Li 2 CO 3 and LiNO 3 will directly affect the phase composition, pore structure and crush load of sintered pebbles. The high-purity Li 2 O ceramic pebbles sintered from Li 2 CO 3 –LiNO 3 precursor pebbles at 730 °C exhibits the open porosity of 24.8 ± 0.7%. The crush load of the ceramic reaches 21.18 ± 1.38 N although the structure was porous. The Li 2 O porous ceramics fabricated in this study will have potential application in tritium breeder materials.

Gd2Zr2O7 nano-grain ceramics with high densities (>90%) and small average grain sizes (66–96 nm) were successfully fabricated for the first time by the fast microwave pressureless sintering method (processing time: 10–90 min). The sintering behavior and microstructural evolution of fluorite structure Gd2Zr2O7 nano-grain ceramics were investigated from 1100 °C to 1300 °C. Comparative analyses were conducted to unveil the influence of temperature and holding time on densification. The results suggest the optimized conditions for sintering dense nano-grain ceramics (66–96 nm) can be achieved at relatively low temperatures ( 1250 °C) and short sintering time (10–60 min). As a demonstration, dense Gd2Zr2O7 ceramics with average grain size of 66 nm were prepared for the first time by rapid microwave pressureless sintering.

Effects of cetyl trimethyl ammonium bromide (CTAB) on the formation of Li2TiO3 nanocrystals during ethanol-water solvothermal reactions were investigated. Addition of CTAB changed Li2TiO3 crystalline morphology from large to small aggregate particles due to the steric repulsion and electrostatic interaction of the CTAB ligands. Aggregate particle size of the Li2TiO3 precursor was reduced from 455.2 to 138.7 nm by preventing their agglomeration after CTAB addition. This was followed by sintering the green body prepared with the CTAB-modified precursor powders using an indirect wet method, then the nanostructured Li2TiO3 ceramic pebbles were obtained at relatively low temperatures from 750 to 800 °C for 4 h. Nanostructured Li2TiO3 ceramic pebbles had small grains and a large number of grain boundaries, which might potentially improve the radiation tolerance, tritium release rate, and mechanical properties of Li2TiO3 tritium breeder pebbles. In addition, grain growth mechanisms as function of different sintering temperatures, crush load as well as relative density of fabricated nanostructured Li2TiO3 ceramic pebbles were also investigated.

MgAlON and AlON powders have been synthesized by carbothermal reduction and nitridation (CRN) from C–Al2O3–7.8 wt% MgO and C–Al2O3 systems, respectively. The phase and morphology of the systems were investigated under 1100–1750 °C via XRD, DTA, SEM and NMR. The results showed that, MgO could significantly effected the stabilization region and morphology of the (Mg)AlON products. The formation of spinel MgAl2O4s intermediate phase was key to obtain MgAlON at lower temperature with smaller particles than that of AlON. Under the optimized compositions, single-phase MgAlON and AlON were obtained at 1600 °C and 1720 °C, respectively. When sintered at 1850 °C for 24 h, the MgAlON sample was clear with highly transparency (82.5% at 3.7 μm), while AlON was opaque with lower transmittance (∼8.0% at 4.7 μm) due to lower sintering activity of the powder.

Ceramics are strong but brittle. According to the classical theories, ceramics are brittle mainly because dislocations are suppressed by cracks. Here, the authors report the combined elastic and plastic deformation measurements of nanoceramics, in which dislocation-mediated stiff and ductile behaviors were detected at room temperature. In the synchrotron-based deformation experiments, a marked slope change is observed in the stress–strain relationship of MgAl2O4 nanoceramics at high pressures, indicating that a deformation mechanism shift occurs in the compression and that the nanoceramics sample is elastically stiffer than its bulk counterpart. The bulk-sized MgAl2O4 shows no texturing at pressures up to 37 GPa, which is compatible with the brittle behaviors of ceramics. Surprisingly, substantial texturing is seen in nanoceramic MgAl2O4 at pressures above 4 GPa. The observed stiffening and texturing indicate that dislocation-mediated mechanisms, usually suppressed in bulk-sized ceramics at low temperature, become operative in nanoceramics. This makes nanoceramics stiff and ductile.

In the present work, highly-transparent aluminum oxynitride (AlON) ceramic has been fabricated by hot isostatic pressing sintering method. SiO2 was used for the first time as a sintering additive for producing highly-transparent AlON ceramics where it plays an effective role to promote the densification during hot isostatic pressing sintering. Furthermore, the optical property of the AlON ceramic is not sensitive to the change of additive concentration when SiO2 was used. All the 3.5 mm thick samples doped with 0.15 wt% ∼0.55 wt% SiO2 showed a high inline transmittance above 86% at 2000 nm. The effects of SiO2 on the phase, lattice parameter, microstructures and hardness of AlON have been investigated in details.

B4C hollow microspheres have been proposed as one of the promising ignition capsules for inertial confinement fusion (ICF). It is worth noting that the selection of easier-to-remove substrate materials is the key to obtaining B4C hollow microspheres. In this work, B4C core-shell microspheres with a uniform structure are prepared by the wet coating method on a PAMS substrate. After the calcination, the complete thermal decomposition of the PAMS substrate leads to a hollow structure B4C ceramic microsphere. The effects of solid content of coating slurry on the morphology and microstructure of the B4C core-shell microspheres were investigated in detail. The result shows that the spacing of the B4C particles in the slurry gradually decreases with increasing the solid content, resulting in an increase in the surface tension of the slurry and an improved stabilization, which helps to optimize the surface roughness and sphericity of the B4C microspheres.

In this paper, a method combining hydrolysis of tetrabutyl orthotitanate (TBOT) and solvothermal reaction was first used to fabricate nanostructured Li2TiO3 tritium breeder ceramic pebbles. Initially, superfine nanostructured Li2TiO3 powders were synthesized with average particle size of about 10 nm, according to TEM. The surface area of precursor particles synthesized via this method was found to be 115.85 m2/g by BET analysis, which is much larger than that of the product obtained using traditional methods. The results showed that precursor particles had high sintering activity. XRD pattern revealed that the phase transition temperature for monoclinic phase Li2TiO3 prepared by this method was nearly 450 °C, which was the lowest phase transition temperature reported among all wet chemical methods to date. Subsequently, investigation of ceramic sintering demonstrated that Li2TiO3 ceramic pebbles with desired nano-crystalline sizes (27.98 ~ 55.03 nm) were obtained by sintering at 500 ~ 600 °C for 4 h. The possible mechanisms were proposed based on the reaction processes of TBOT hydrolysis, solvothermal reaction and sintering.

Using Nd and Ce with the ratio of 1:5 as simultaneous substitutions of trivalent and tetravalent actinides in gadolinium zirconate, a series of Gd2-xNdxZr2-5xCe5xO7 (0 ≤ x ≤ 0.4) ceramics were prepared by rapid microwave sintering with a co-precipitation assisted solvothermal synthesized nanocrystalline powders. The simulated proportional nuclear waste disposal behaviours were identified by various characterization methods. XRD results show that when x is less than 0.4, all samples only have the single defect fluorite structure, while Gd1.2Ce0.8O3.2 is formed in Gd1.6Nd0.4Ce2O7 as x raise to 0.4. The relative density and average grain size both increase with the elevation of sintered temperature and x value. Sintering maps show that the obvious grain growth happens when x ≥ 0.3 and the densification processes can occur at different sintering temperatures with different x values.

Shock impedance matching between transparent ceramic windows and shock-loaded metal materials is the fundamental requirement for constructing a highly confident equation of state (EOS) for samples testing. The new ZnxMg1-xAl2O4 spinel system has a wide range of shock impedance and a high pressure range transparency. In this paper, the shock impedance of ZnxMg1-xAl2O4 spinel was designed by density functional theory (DFT). The results show that the ZnxMg1-xAl2O4 system has good transparency in the test range of

Yttrium-stabilized zirconia (Y0.08Zr0.92O1.96, YSZ) nanocrystalline powders were prepared by co-precipitation methods. Different precipitants (ammonium hydroxide, ammonium bicarbonate, oxalic acid, and urea) were used to study the effects of precipitants on co-precipitation synthesis of YSZ nanocrystalline powders. Thermogravimetric analysis-differential scanning calorimetry, powder X-ray diffraction, Fourier-transform infrared, scanning electron microscope, energy-dispersive spectrometer, Brunauer–Emmett–Teller, Barrett–Joyner–Halenda, and X-ray photoelectron spectroscopy analysis methods were employed to investigate the thermal decompositions, phase evolutions, micro-morphologies, surface areas, and elements analysis of the synthesized YSZ precursor powders or nanoparticles. Although different precipitants were used, the calcined products at 600 °C have nearly identical chemical compositions. The crystallization temperature of the precursor powders to evolve to cubic phase is the lowest (about 400 °C) when ammonium hydroxide is used as a precipitant, while it is about 500 °C in the case of other three types of precipitants (ammonium bicarbonate, oxalic acid, and urea) that were used. Ammonium bicarbonate cannot precipitate ZrO2+ effectively in the solution, resulting in the formation of cubic Y0.18Zr0.82O1.91 at 1000 °C. Despite the time-consuming co-precipitation process, urea was proved to be the optimal precipitant in terms of the fabrication of nanocrystalline YSZ powders with designed Y/Zr/O molar ratio, large surface area, small crystallite size, and well dispersion.

Highly transparent LaGdZr2O7 ceramics were fabricated by solid reactive sintering using the ball-milling mixed raw powder, and the transparency of samples can be significantly enhanced by optimizing the ball-to-powder weight ratio. The ratio effects on the evolution of morphology and particle size distribution of mixed powder, as well as the relative density and the in-line transmittance of obtained LaGdZr2O7 ceramics were investigated in detail. As the ratio increased above 24:1, the uniform and spherical-like particles became platy particles with bimodal particle size distribution (platy bimodal powder), while the relative density and transmittance of the LaGdZr2O7 ceramics were obviously improved. The highest in-line transmittance of 74.8% at 1100 nm, about 94% of the theoretical transmittance, can be achieved when milling ratio 27:1 was employed. Combined with the high refractive index (2.08 at 632.8 nm), high density (6.446 g/cm3) and high effective atomic number, the highly transparent LaGdZr2O7 ceramics obtained in this work can find potential applications in many areas such as optical lens and promising candidates for scintillator host, etc.

In order to efficiently grasp the tritium behavior in advanced core–shell breeding materials, this study adopts a route of injecting tritium out-of-pile to deal with the problems of fewer platforms, long periods, and high costs for traditional neutron irradiation-tritium release experiments. Here, tritium adsorption and desorption experiments were carried out with Li4TiO4–Li2TiO3 core–shell breeding materials before and after long-term heating up to 30 days. The purpose is to study whether the structural changes caused by long-term heating will affect the adsorption and desorption behavior of tritium on the sample surface. The results show that the lack of chemically adsorbed water caused by long-term heating will significantly weaken the tritium adsorption capacity of the sample, but will not affect the desorption behavior of Ar, 1% H2 + Ar and water vapor on tritium, so all samples show a very low tritium retention.

Hetero-element doped lithium orthosilicates have been considered as advanced tritium breeders due to the superior performances. In this work, Li4Si1−xTixO4 ceramics were prepared by proprietary hydrothermal process and multistage reactive sintering. The reaction mechanism of Li4Si1−xTixO4 was put forward. XRD and SEM analyses indicate that insertion of Ti leads to lattice expansion, which promotes the grain growth and changes the fracture mode. The compressive tests show that the crush load increases almost four times by increasing x from 0 to 0.2. However, the thermal conductivity and ionic conductivity are the best when x = 0.05 and x = 0.1, respectively. Thermal cycling stability of Li4Si1−xTixO4 pebbles was further appraised through investigating the changes of microstructure and crush load. After undergoing thermal cycling, the Li4Si1−xTixO4 still show higher crush load compared with Li4SiO4, despite Ti segregation in some samples. The x = 0.05 sample exhibits excellent thermal cycling stability. In summary, proper amount of Ti doping can improve the crush load, thermal and ionic conductivity, and thermal cycling stability of Li4SiO4.

Defining the energetic landscape of pseudocapacitive materials such as transition metal layered double hydroxides (LDHs) upon redox-site enrichment is essential to harnessing their power for effective energy storage. Here, coupling acid solution calorimetry, in situ XRD, and in situ DRIFTS, we demonstrate that as the Ni/Al ratio increases, both as-made (hydrated) and dehydrated NiAl-LDH samples are less stable as evidenced by their enthalpies of formation. Moreover, the higher specific capacity at an intermediate Ni/Al ratio of 3 is enabled by effective water-LDH interactions, which energetically stabilize the excessive near-surface Ni redox sites, solvate intercalated carbonate ions, and fill the expanded vdW gap, paying for the "energetic cost" of being "redox-site-rich". Thus, from a thermodynamic perspective, engineering molecule/solid-LDH interactions on the nanoscale with confined guest species other than water, which energetically impose stronger stabilization, may help us to achieve their specific capacitance potential., Gene and Linda Voiland School of Chemical Engineering and Bioengineering; Chambroad Distinguished Fellowship; Achievement Rewards for College Scientists (ARCS) Fellowship from the ARCS Seattle Chapter; U.S. Department of Energy's NNSANational Nuclear Security Administration [89233218CNA000001]; Alexandra Navrotsky Institute for Experimental Thermodynamics at Washington State University, This work was supported by institutional funds from the Gene and Linda Voiland School of Chemical Engineering and Bioengineering and fund of the Alexandra Navrotsky Institute for Experimental Thermodynamics at Washington State University. X.Z. is supported by the Chambroad Distinguished Fellowship. C.B.C. received support from the Achievement Rewards for College Scientists (ARCS) Fellowship from the ARCS Seattle Chapter. This work was performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science. Los Alamos National Laboratory, an affirmative action equal opportunity employer, is managed by Triad National Security, LLC for the U.S. Department of Energy's NNSA, under contract 89233218CNA000001.

Defining the energetic landscape of pseudocapacitive materials such as transition metal layered double hydroxides (LDHs) upon redox site enrichment is essential to harness their power for effective energy storage. Here, coupling acid solution calorimetry, in situ XRD, and in situ DRIFTS, we demonstrate that as the Ni/Al ratio increases, both as-made (hydrated) and dehydrated NiAl-LDH samples are less stable evidenced by their enthalpies of formation. Moreover, the higher specific capacity at intermediate Ni/Al ratio of 3 is enabled by effective water – LDH interactions, which energetically stabilizes the excessive near-surface Ni redox sites, solvates intercalated carbonate ions, and fills the expanded vdW gap, paying for the “energetic cost” of being “redox site rich”. Thus, from a thermodynamic perspective, engineering molecule/solids – LDH interactions on the nanoscale with confined guest species other than water, which energetically impose stronger stabilization, may help us to achieve their specific capacitance potential.

Gadolinium zirconate (Gd2Zr2O7) is a candidate phase of ceramic waste form for immobilizing high-level nuclear waste. Dense fine-grained ceramics is beneficial to improve the irradiation resistance and leaching resistance of the ceramic waste form. In this work, two-step microwave sintering (TSMS) on Gd2Zr2O7 was firstly demonstrated as a considerable approach to fabricate dense nano-grained Gd2Zr2O7 ceramic. Microstructure evolutions and densification processes of the Gd2Zr2O7 samples at various temperatures were investigated. The nano-grained (69.2 nm) Gd2Zr2O7 ceramic with a relative density of 96.9% has been successfully fabricated at 1350 °C - 3 min - 1200 °C - 20 min. TSMS can promote the near complete densification of ceramics while suppressing the growth of crystal grains within nanoscale (

Highly transparent Yb:YAG laser ceramics with various Yb3+ doping level were successfully fabricated through vacuum sintering of co-precipitated powders in combination with the hot isostatic pressing process. The effects of various Yb3+ dopant concentrations (1–15 at.%) on the photoluminescence, terahertz absorption and optical characteristics of Yb:YAG transparent ceramics were investigated. Characterizations of the Near-IR photoluminescence emission and kinetics of the Yb:YAG ceramics revealed the corresponding 2F5/2 → 2F7/2 characteristic bands of Yb3+ and the lifetime enhanced with increasing Yb3+ dopant concentrations, confirming no concentration quenching effect in Yb:YAG. Measurements of terahertz absorption properties of Yb:YAG transparent ceramics by a time-domain spectroscopy evidenced that both the cutoff frequency and terahertz absorption coefficient of Yb:YAG samples depended upon the Yb3+ dopant concentrations. The underlying mechanisms by which such Yb3+ dopant concentrations affected the terahertz absorption and optical properties were also discussed. The optical attenuation loss values were measured at 1064 nm for all the samples, to be ∼0.030 cm−1, a value close to that observed for single crystal.

Electron beam evaporation (EBE) deposition technique was employed to prepare amorphous boron carbide thin films at room temperature. In this work, a new contribution to the knowledge of deposition time dependence of stoichiometric was reported. The results indicated that the thickness of the amorphous boron carbide thin films were approximately 87–830 nm with a deposition time of 20–120 min. The growth mode of the film is layer-island growth. The XPS analysis demonstrated the B/C atomic ratio increased with the increasing of deposition time due to the different evaporation behaviors between B and C atoms in EBE processes. The stoichiometry of amorphous boron carbide thin films was controlled in the range of 1.3 ± 0.1–3.1 ± 0.1 via electron beam evaporation by the deposition time of 20–120 min. This work will be useful to advance the application of amorphous boron carbide thin films as an ICF ablator, and has a certain reference value for electron beams to evaporate other compounds.

In this work, we report a rapid, simple and controllable approach to prepare B4C ceramic double-curvature shells by dropping the coating slurry on a molybdenum (Mo) substrate. The B4C slurry finally forms a nearly uniform spherical thin shell on the Mo substrates after drainage and curing process. We discovered that the uniformity and the wall thickness of the thin shell structure are controlled by the curing time and the viscosity of the slurry, respectively. This novel fabrication method not only provides an alternative way to prepare B4C ceramic double-curvature shells for the potential application as an ICF capsule, but also sheds light on the uniformity control of other ceramic double-curvature thin shells.

Li4TiO4 ceramics pebbles have been proposed to be a promising tritium breeder materials for the fusion reactor blanket of the International Thermonuclear Experimental Reactor (ITER). In the present study, the hydrothermal method was first used to synthesize the nanostructured precursor powders for fabricating the Li4TiO4 ceramic pebbles. The precursor powders were composed of LiOH, Li2CO3 and Li2TiO3 with a grain size of 30–80 nm. Moreover, the microstructure and phase evolution of Li4TiO4 ceramics pebbles were investigated. The results indicated that the formation temperature of Li4TiO4 by hydrothermal method was lower than that of other methods. The pure phase Li4TiO4 ceramic pebbles with small grain size (average value 0.50 μm), satisfactory crush load (average value 41 N) and reasonable pore structure was sintered at 750 °C for 4 h in vacuum. This study provides a new method for preparing a high quality Li4TiO4 ceramic pebble, which has potential application as a tritium breeding material.

Transparent AlON ceramics are intriguing window materials with excellent mechanical strength and superb optical transparency from the near ultraviolet to the mid-infrared range. However, previous studies focused their investigations in the visible range; therefore, the application of transparent AlON ceramics to tunable windows has yet to be reported. In this work, a VO2 thin film with a characteristic semiconductor-metal phase transition (SMT) was fabricated on a transparent AlON ceramic, which exhibited remarkable tunable switching properties in the infrared and terahertz ranges. The transparent AlON ceramic was prepared by a two-step method, which included carbothermal reduction and pressureless sintering. The resulting ceramic exhibited high transparency of over 70% in the visible-infrared range and a notable THz transmission of 64.5–73.9% at 0.1–1.5 THz. The VO2 thin film was prepared on a transparent AlON ceramic using the sol-gel method and showed excellent optical and electric switching performance. The square resistance variance was close to four orders of magnitude, and an infrared switching ratio of over 40% was obtained. Furthermore, the combined structure showed an efficient THz switching ratio of approximately 70.9%. This study proposes a composite material combined with a transparent ceramic and a phase transition oxide and provides great insights into their application in infrared and terahertz smart windows as well as in switching devices.

Uranium doped yttrium aluminum garnet (YAG) transparent ceramic with Ca2+ as charge compensator and sintering aid was firstly fabricated by vacuum sintering technique using the co-precipitation synthesis of raw powders. The structural, optical spectral and luminescence properties of the U:YAG ceramic have been investigated in detail. The experimental results show that uranium doped in YAG matrix has not changed the crystal structure. Vacuum sintering 15 h in 1800 °C, the sample has a pore-free structure with an average grain size of about 3.5 μm, and in-line transmittance reaches up to 78% in the visible wavelength region. The excitation spectrum showed a sharp band around 458 nm, and the emission spectrum revealed the intense green emission located at 520 nm. Further, with respect to the shape of emission band and luminescence color, uranium was inferred to exist as uranate ion (UO66−) in the YAG host where it replaces the ‘Y’ ions at dodecahedral site with surrounding defect centers created for charge compensation.

The color center and optical characteristics of Yb:YAG transparent ceramic were investigated for various cation additives (Si4+, Mg2+ and Si4+ + Mg2+). The presence of a population of free electrons in the vacuum sintered Yb:YAG ceramics without additives, which imparted a green color and promoted the formation of Yb2+-F+ centers. The introduction of Si4+ additives were unable to remove the [Yb2+-F+] composite color centers. Theoretical analysis and experimental proofs revealed that the cation additives containing ions aliovalent to YAG introduces vacancies, which in turn induce the formation of Re2+-F+ (Re2+: Yb2+, Mg2+ or Ca2+) composite color centers. It was also demonstrated that the addition of a combination MgO + SiO2 sintering aid serves to inhibit abnormal grain growth and enhance densification, accompanied with the elimination of color centers. Furthermore, the underlying mechanisms by which these aliovalent cation additives influence color center formation and optical properties are discussed in detail. The lowest optical attenuation loss was measured at 1064 nm in Yb:YAG ceramic with the MgO + SiO2 additives, to be 0.0031 cm−1, a value close to that observed for single crystals.

LaGdZr2O7 transparent ceramics were fabricated by the vacuum sintering method using the precursor made from coprecipitation synthesis. The effects of calcination temperature on cation ordering and the morphology of LaGdZr2O7 powders, as well as the microstructure and transmittance of the LaGdZr2O7 ceramics, were investigated. As the calcination temperature for LaGdZr2O7 powder preparation increased from 1000 °C to 1300 °C, the domain and particle size increased, and the cations [(La1/2Gd1/2)3+-Zr4+] became more ordered. The LaGdZr2O7 powders calcined from 1150 °C to 1200 °C showed weak agglomeration and gave the best sintering manner for fabricating transparent ceramics. LaGdZr2O7 transparent ceramics with an in-line transmittance of 73–75% (at 1200 nm) were obtained from the LaGdZr2O7 powder sintered at 1800 °C in vacuum for 10 h. The scattering of pores should be responsible for the low transmittance of LaGdZr2O7 ceramics in the current study.

As an advanced tritium breeder material for the fusion reactor blanket of the International Thermonuclear Experimental Reactor (ITER), Li 2 TiO 3 -Li 4 SiO 4 biphasic ceramic has attracted widely attention due to its merits. In this paper, the uniform precursor powders were prepared by hydrothermal method, and nanostructured 2Li 2 TiO 3 -Li 4 SiO 4 biphasic ceramic pebbles were fabricated by an indirect wet method at the first time. In addition, the composition dependence (x/y) of their microstructure characteristics and mechanical properties were investigated. The results indicated that the crush load of biphasic ceramic pebbles was better than that of single phase ceramic pebbles under identical conditions. The 2Li 2 TiO 3 -Li 4 SiO 4 ceramic pebbles have good morphology, small grain size (90 nm), satisfactory crush load (37.8 N) and relative density (81.8 %T.D.), which could be a promising breeding material in the future fusion reactor.

A facile solvothermal method has been developed to synthesize Gd 2 Zr 2 O 7 nanopowders with well-controlled particle size and dispersion. The nanopowders were consolidated into dense ceramic pellets by pressureless sintering, and effects of the solvothermal method in microstructure control are demonstrated by comparison with conventional precipitation approach. X-ray diffraction, electron microscopy, gas adsorption, and a standard operating procedure (SOP) in Malvern Instruments were employed to investigate crystallite/grain sizes and structural morphology evolutions of nanopowders and ceramics. Well-crystallized Gd 2 Zr 2 O 7 nanopowders with little agglomeration and narrow size distribution synthesized by this method have an average crystallite size of 3.5 nm and high surface area of 162 m 2 /g. This method also allows the formation of homogeneous and dense Gd 2 Zr 2 O 7 ceramic with bulk density over 94% of the theoretical value achieved after sintering at 1500 °C for 6 h.

Transparent alumina (Al 2 O 3 ) ceramic wafers are frequently applied in industry, however it is usually difficult to obtain a high-quality transparent alumina ceramic wafer without any deformation. Here we present a nonaqueous tape-casting method, which is followed by a presureless vacuum sintering process, to fabricate the transparent alumina ceramic wafers with restrained or eliminated undesired deformation or cracking. By using scanning electron microscope, we observe the microscopic morphologies of green tapes and sintered wafers from various different laminate methods, including cold pressing, cold isostatic pressing, warm pressing, and the combinations of warm pressing plus cold isostatic pressing. We find that the warm pressing pretreatment has an impressive optimization effect on the microscopic morphologies of the green tapes due to the properties of thermoplastic structure in the green tape, and also plays a promotional role in wafer densification process. With the optimized green tapes which are dense and uniform, transparent alumina ceramic wafers with a thickness of 500 µm and the lateral size of 63 mm × 63 mm without any deformation or cracking were successfully fabricated. We also examine the transmittance properties of the as-prepared wafer, and find that our obtained transparent alumina ceramic wafers without deformation or cracking have no loss of good transmittance in contrast to previous work.

Via a powder pretreatment process, transparent La0.4Gd1.6Zr2O7 ceramics were successfully fabricated through the aqueous AM (acrylamide) gel-casting technique. Our research shows that the water absorption of La2O3 has significant influence on the viscosity of slurry, leading to low density of the green body and poor transparency of ceramic. By pretreating the mixed powder via a solid-state reaction, the viscosity and pH results have shown that the single-phase pretreated powder has a positive improvement on the gel-casting process. Compared with the mixed powder, the pretreating method has effectively improved the slurry with higher solid content and lower viscosity. Therefore, the pretreated powder combined with gel-casting method have a positive influence on the density of green body and the optical quality of obtained La0.4Gd1.6Zr2O7 ceramics. The polished ceramics with 40 mm in diameter (O = 40 mm) and 1.5 mm in thickness (δ = 1.5 mm) exhibited the in-line transmittance of 78% at 1100 nm and a maximum transmittance of about 80% in the infrared region, as well as a wide range of high stable transmittance among 0.6–6.0 µm wavelength. Our work opens a way for highly transparent ceramic preparation by aqueous AM gelling system with hygroscopic rare earth oxide as raw materials.

Via a vacuum sintering method, highly transparent Ho: Y2Zr2O7 ceramics with different holmium doping concentrations were successfully fabricated for the first time. Y1.99Ho0.01Zr2O7 and Y1.98Ho0.02Zr2O7 transparent ceramics exhibit the highest in-line transmittance at 72% in the visible (Vis) region and over 75% in the near infrared (NIR) region. The microstructure and crystal structure of Ho: Y2Zr2O7 transparent ceramics were fully investigated by SEM and XRD measurements. Photoluminescence spectra demonstrated that Ho: Y2Zr2O7 ceramics can be effectively excited at 376 nm and 460 nm. Strong green (centered at 551 nm) and NIR (centered at 1111 nm) emissions were observed in the downshifting (DS) luminescence. Meanwhile, same green emissions have been observed in the upconversion (UC) luminescence. The luminescence decay curves have also been studied, demonstrating that the longest average fluorescence lifetime of Ho: Y2Zr2O7 transparent ceramics reaches 48 μs. Combined with the high temperature resistance and good mechanical strength of Y2Zr2O7 transparent ceramics, these results suggest that Ho3+: Y2Zr2O7 transparent ceramics are able to generates both down and up converted fluorescence.

In shock wave precision physical measurements, the shock impedance of sapphire (Al2O3) transparent windows and Fe samples cannot be completely matched, which seriously affects the measurement accuracy. Adjusting the components of the anion and cation in the γ-Al2O3 structure is a possible solution. N3- and Mg2+ were introduced into the γ-Al2O3 matrix to form Al(8+x)/3□(1/3-x/3)O4-xNx (□ denotes the vacancy, AlON) or Mg1-yAl2+yO4-yNy (MgAlON). Using the first-principles method coupled with the shock wave theory, the shock response behaviors and optical properties of AlON and MgAlON were studied in this work. Due to a more obvious effect was induced by Mg2+ than N3-, MgAlON had a wider shock impedance adjustment range compared with AlON. The simulation results of the shock pressure-particle velocity curves (σxx-U) demonstrated that the shock impedance of MgAlON can be completely matched with that of the Fe samples in a wide pressure range (0–20 GPa) by tuning its composition. In addition, AlON and MgAlON show good transparency between 0 and 20 GPa. This discovery provides theoretical guidance for selecting transparent ceramic windows with optimized structures and compositions that match the shock impedance of the Fe samples.

For Gd 2 Zr 2 O 7 , nanograin ceramics with high relative densities (95%–97.4%) and small average grain sizes (61 nm - 82 nm) were successfully fabricated for the first time using field assisted sintering technique (FAST), also known as spark plasma sintering (SPS) method, in which nanopowders with an average crystallite size of 5.9 nm were synthesized via a non-aqueous gel-combustion method. Temperature was varied over a broad range to investigate its influence on the densification mechanism, microstructure evolution and hardness. The results revealed that both relative density and grain size increase with the increase of sintering temperature. The densification processes were divided to three stages. 1250 °C–1300 °C is the most suitable temperature range to fabricate dense Gd 2 Zr 2 O 7 nanograin ceramics with comparatively high hardness by FAST.

Transparent polycrystalline Yb/Er:YAG and Yb, Er:YAG ceramics with different Er 3+ concentration were successfully fabricated by vacuum sintering co-precipitated raw powders. The structural, optical, and spectroscopic properties of the Er:YAG and Yb, Er:YAG ceramics were investigated in detail. The absorption coefficient of the Er:YAG ceramics increased with the increase of Er 3+ dopant level. The absorption coefficient of Yb, Er:YAG ceramic at ~970 nm (0.967 cm −1 ) is nearly 4.5 times the value for Er:YAG ceramic of 0.214 cm −1 . The upconversion luminescence spectra, infrared luminescence spectra, and fluorescence lifetimes of the ceramics were also studied. Results show that the intense green and red emissions located at around 523, 560 and 677 nm are attributed to the radiant transitions of 2 H 11/2 / 4 S 3/2 - 4 I 15/2 and 4 F 9/2 - 4 I 15/2 of Er 3+ , respectively. The infrared spectra presented many narrow emission peaks in the 1450–1700 nm regions, attributable to the 4 I 13/2 - 4 I 15/2 emission transition. The fluorescence lifetime of the Yb, Er:YAG ceramic (7.53 ms) is also greater than that of Er:YAG (6.67 ms). Furthermore, the underlying mechanism of the IR and visible emission bands were discussed. Experimental results provided evidence that energy transfer from Yb 3+ to Er 3+ can be achieved, indicating Yb, Er:YAG ceramic could be a potential lasing medium material.

Single-phase nano-crystalline yttria-stabilized zirconia (YSZ) powder was prepared by co-precipitation method using zirconium oxychloride (ZrOCl₂ · 8H₂O) and yttrium nitrate (Y(NO₃)₃ · 6H₂O) as raw materials and ammonium bicarbonate (NH₄HCO₃) and liquor ammonia (NH4OH) as the precipitators. In order to get the powder with favorable dispersibility, polyethylene glycol (PEG, HO(CH₂CH₂O) n H) with different molecular weights and amounts was used as a dispersant agent in the synthesis process and its effects on the YSZ powder was investigated. The scanning electron micrograph (SEM) images showed that the degree of agglomeration and the mean crystal size of YSZ powder varied with the amount and the molecular weight of PEG. The appropriate amount and molecular weight of PEG were given by comparing the dispersibility and crystal size distribution of powders. In the process, one also could find that the promotion of dispersion was insensitive to the molecular weight, and all PEG (400–2000) can exert an ability to reduce the agglomeration. The proper amount of PEG400, PEG600, PEG1000, PEG2000 was 3 wt%, 3 wt%, 2 wt%, 2 wt%, respectively. The transmission electric microscope studies in conjunction with the XRD analyzes verified the low degree of agglomeration and the size of YSZ powder varied between 10~20 nm.

Gd2Zr2O7 nanoceramics were fabricated using pressureless sintering method, in which the nanopowders were synthesized via solvothermal approach. The effects of starting powders on grain growth and densification during sintering of ceramics were revealed. Two distinct pressureless sintering methods were investigated, including conventional and two-step sintering. The sample grain size increases abruptly as sintering temperature increases during conventional sintering. In contrast, in two-step sintering, abnormal or discontinuous grain growth was suppressed in the second step, leading to Gd2Zr2O7 nanoceramics formation (average grain size 83 nm, relative density ∼93%). Such distinct behaviors may originate from the interplay between kinetic factors such as grain boundary migration and diffusion. Moreover, suppression of grain growth and promotion of densification in the two-step sintering are mainly due to dominant role of grain boundary diffusion during the second-step sintering process.

Defect-fluorite structured Gd2Zr2O7 nanoparticles were successfully synthesized via a homogeneous precipitation-solvothermal method using urea as a precipitant. The obtained nanoparticles were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) analysis and transmission electron microscopy (TEM). Compared to the traditional solvothermal method, this homogeneous precipitation-solvothermal method has the advantage of producing nanoparticles with small grain sizes, a narrow size-distribution, high surface areas and little agglomeration. Particularly, the mean crystallite size of Gd2Zr2O7 obtained by this method is 20–30 nm, providing a great opportunity of using these nanoparticles as starting nano-sized building blocks for low temperature preparation of homogeneous and dense ceramics.

Aluminum oxynitride (AlON) transparent ceramics were prepared through aqueous gel-casting forming technique. To prevent hydrolysis, the homemade AlON powder was treated in 1% phosphoric acid at 70 °C for 30 min. Then the surface-treated AlON powder was dispersed in an aqueous-organic solution to prepare low viscosity slurry with 40 vol% solids loading, which was shaped by gel-casting forming technique. The hydrolysis of AlON powder was prevented effectively and the transmittance of sintered ceramics had been significantly improved by introducing hydrolysis protection of the powder. The sample sintered with the treated powder can reach an ultimate infrared transmittance of 78% with 2 mm thickness. The surface modification of AlON powder with phosphoric acid was confirmed by various techniques such as scanning electron microscopy (SEM), pH, Viscosity, X-ray photoelectron spectroscopy (XPS) and infra-red spectroscopy (IR). The related hydrolysis protection mechanism via this available method was discussed.

In this work, transparent sub-mircon Gd2Zr2O7 (GZO) ceramic was successfully sintered for the first time by spark plasma sintering (SPS) using nanocrystalline powders synthesized via a solvothermal assisted co-precipitation route. With the aids of fast heating and cooling rate and high pressure, the GZO transparent sample with an average grain size of about 205 nm was obtained at 1400 °C for 5 min. The maximum transmittance of about 70% was achieved at a wavelength of 2000 nm.