On fast LuAG:Ce scintillation ceramics with Ca2+ co-dopants

“Defect engineering” was a valid strategy to modify the performance of LuAG:Ce scintillator, usually realized by Me²⁺/Me⁺ co-doping. To investigate the effects of Ca²⁺ co-doping on the scintillation properties of LuAG:Ce, a set of LuAG:Ce ceramics with Ca²⁺ concentrations ranging from 0 to 0.5 at.% were manufactured. The absorption spectra, radioluminescence spectra (RL spectra), light yield, RL spectra as a function of temperature, decay time, and TSL curves of the ceramic products were carefully measured. With Ca²⁺ co-doping, the scintillation performance of LuAG:Ce ceramics was greatly improved. Especially for the 0.2 at.% Ca²⁺ co-doped one, it has a high light yield value of 24, 400 ph/MeV, a fast scintillation decay time of 48 ns, and a small slow component contamination. And the role of Ca²⁺ in the scintillation mechanism of LuAG:Ce ceramics was also discussed in this paper.     

Fabrication and Scintillation Performance of Nonstoichiometric LuAG:Ce Ceramics

Nonstoichiometric LuAG:Ce Ceramics ([Lu_(1–x)Ce_x]₃Al₅O₁₂, x = 0.005) with different excess of Lu³⁺ were designed on the basis of Lu₂O₃‐Al₂O₃ phase diagram and fabricated by a solid‐state reaction method. Without using any traditional sintering aids, pure phase and good optical performance were obtained in such a Lu‐rich LuAG:Ce ceramics. In addition, scintillation efficiency and light yield of 1% excess of Lu³⁺ ceramic sample were found 16 times and 1.82 times higher than that of commercial Bi₄Ge₃O₁₂ (BGO) single crystals, respectively. Such values are comparable or even better than those in most of LuAG:Ce single crystals. However, antisite defects were also induced by excess of Lu doping, whose luminescence was found at 350–410 nm in Lu‐rich LuAG:Ce ceramics. The relationship of excess content of Lu and the microstructure, optical quality, and scintillation performance were clarified and discussed. Furthermore, by utilizing X‐ray absorption near edge spectroscopy technique, the charge state stability of cerium in Lu‐rich LuAG:Ce ceramics was examined. It appears that the excess of isovalence Lu³⁺ doping has a negligible effect on the cerium valence instability and creation of stable Ce⁴⁺ center.     

Phase Formation and Enhanced Dielectric Response of Y2/3Cu3Ti4O12 Ceramics Derived from the Sol–Gel Process

Y_2/3Cu₃Ti₄O₁₂ (YCTO) ceramics were successfully synthesized by sol–gel method (SG) and solid‐state method (SS), respectively. The optimized processing parameters for the syntheses of precursor powders by sol–gel process were determined as follows: the Ti(OC₄H₉)₄ concentration was 0.50 mol/L, the CH₃COOH volume was 8 mL, and the volume percentage of H₂O was 11.2%. Particularly, on the basis of XRD and TG‐DSC analyses, the phase formation temperature of YCTO‐SG was at least 100°C lower than that of YCTO‐SS. YCTO‐SG ceramics sintered at 1060°C for 25 h showed fine‐grained microstructure, and higher dielectric constant (ε′ ≈ 5.24 × 10⁴) at 1 kHz compared to YCTO‐SS ceramics (ε′ ≈ 0.93 × 10⁴). The higher dielectric constant of the YCTO‐SG ceramics was attributed to the grain size effect. Furthermore, the YCTO‐SG ceramics showed a distinct high‐temperature (>300°C) relaxor‐like behavior. According to the calculated activation energy value, the single ionization of oxygen vacancies was responsible for the conduction and dielectric anomaly behaviors of YCTO‐SG ceramics.     

Large electric‐field‐induced strain and enhanced piezoelectric constant in CuO‐modified BiFeO3‐BaTiO3 ceramics

In this work, we fabricated the (1‐x)BiFeO₃‐xBaTiO₃+y‰ mol CuO ceramics by the modified thermal quenching technique. The pure perovskite phase was formed and a morphotropic phase boundary (MPB) was observed in the ceramics with x = 0.30‐0.33. The addition of CuO can significantly enhance the density of the BiFeO₃‐BaTiO₃ material. Importantly, an enhanced piezoelectric constant (d₃₃=165 pC/N), a large electric‐field‐induced strain (?S = 0.54%: peak to peak strain) and a large piezoelectric actuator constant (d₃₃*=449 pm/V) together with a high Curie temperature (T_C) of 503°C were observed in the ceramics with x = 0.30 and y = 5. As a result, the enhanced piezoelectricity and large electric‐field‐induced strain could significantly stimulate further researches in BFO‐based ceramics.     

Wavelength Tailorability of Broadband Near‐Infrared Luminescence in Cr4+‐Activated Transparent Glass‐Ceramics

Four Cr⁴⁺‐activated transparent glass‐ceramics containing different species of silicate nano‐crystals (Zn₂SiO₄, Mg₂SiO₄, Li₂ZnSiO₄, and Li₂MgSiO₄) were successfully prepared. Absorption spectra, photoluminescence spectra, lifetime decay curves, and quantum yield of these transparent glass‐ceramics were measured. According to the crystal field strength of Cr⁴⁺‐incorporated tetrahedral sites, the broadband near‐infrared (NIR) luminescence of Cr⁴⁺ can be tailored from 1130 to 1350 nm and the lifetime of Cr⁴⁺ luminescence can be prolonged from 6 to 100 μs. Quantum yield in the transparent glass‐ceramics containing Li₂ZnSiO₄ nano‐crystals reached at 17%, which is the highest value of NIR luminescence in transition‐metal‐activated glass materials.     

Fast Ce,Ca:LuAG scintillation ceramics for HEP: Fabrication,characterization, and computation

High-energy physics community is looking for a hard, fast, and low-cost scintillation material, and Ce:Lu₃Al₅O₁₂ (Ce:LuAG) ceramic is one of the competitive candidates. This work presents Ce,Ca:LuAG scintillation ceramics with good optical quality, and the influence of Ce and Ca concentrations on optical and scintillation properties was fully analyzed. At relatively low level of Ce concentration, the less Ca²⁺ content is needed to achieve a significant intensity increase in fast scintillation component while maintaining a relatively high light yield (LY). The introduction of only 0.1 at% Ca²⁺ could increase the LY_{0.5 μs}/LY_{3.0 μs} from 79.9% to 96.1% in Ce,Ca:LuAG ceramics of 0.1 at% Ce. First-principles investigations are further performed to reveal the tuning mechanisms of the scintillation properties of LuAG by Ce and Ca codoping. We show that the Fermi level shifts down with Ca codoping, which increases the Ce⁴⁺ content and decreases the depth of the electron traps (V_O), resulting to a faster decay. Moreover, the formation preference of Ca-V_O complexes over Ce-V_O leads to the suppression of the non-radiative decay of Ce via V_O. In summary, our study demonstrates the realization of the performance tuning of LuAG via Ce and Ca codoping.     

Porous PZT Ceramics with Aligned Pore Channels for Energy Harvesting Applications

In this study, aligned porous lead zirconate titanate (PZT) ceramics with high pyroelectric figures‐of‐merit were successfully manufactured by freeze casting using water‐based suspensions. The introduction of aligned pores was demonstrated to have a strong influence on the resultant porous ceramics, in terms of mechanical, dielectric, and pyroelectric properties. As the level of porosity was increased, the relative permittivity decreased, whereas the Curie temperature and dielectric loss increased. The aligned porous structure exhibited improvement in the compressive strength ranging from 19 to 35 MPa, leading to easier handling, better processability and wider applications for such type of porous material. Both types of pyroelectric harvesting figures‐of‐merit (F_E and F′_E) of the PZT ceramics with a porosity level of 25–45 vol% increased in all porous ceramics, for example, from 11.41 to 12.43 pJ/m³/K² and 1.94 to 6.57 pm³/J, respectively, at 25°C, which were shown to be higher than the dense PZT counterpart.     

Thermoelectric Efficiency of Reduced SrTiO3 Ceramics Modified with La and Nb

Ceramics of La_xSr_1?xNb_yTi_1?yO₃ (LSNT) were synthesized under various reducing atmospheres. Covering the specimens with graphite carbon felt under an Ar‐gas flow during sintering drastically enhanced the electrical conductivity, σ. Ti K‐edge absorption spectra indicated the presence of Ti³⁺ for heavily reduced specimens. The increase in conductivity was attributed to the 3d band of Ti³⁺. The maximum value for the figure of merit, ZT, was obtained for strontium titanate ceramics modified with both 5 mol% La and 5 mol% Nb, namely 5/5‐LSNT, exhibiting a ZT value of ~0.221 at 473 K. This high ZT value was almost 1.5 × larger than that of the conventional 10 mol% La‐doped sample, 10/0‐LSNT (ZT~0.144), and was mainly attributed to the larger Seebeck coefficient of the material.     

Transparent cobalt-doped yttrium aluminum garnet (Co2+:YAG) ceramics—An innovatory fast saturable absorber

Highly transparent Y₃Al₅O₁₂ (YAG) ceramics doped with 0.025 and 0.05 at.% Co ions were prepared for the first time by the freeze granulation process and reaction sintering. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were performed to analyze the microstructure and crystal structure of the samples. The absorption spectra of the Co²⁺:YAG ceramics were measured at room temperature, and significant absorption bands at 600 nm, as well as at 1535 nm, were observed. The nonlinear behavior of the received material was experimentally demonstrated. Due to the short relaxation time of investigated ceramics, we considered them as fast saturable absorbers. The influence of the postsintering annealing process was examined. The values of saturation intensities of YAG ceramics with different concentrations of cobalt were estimated by fitting experimental data to the theoretical model for fast saturable absorbers.     

Mechanical Behavior and Applications of Plasma Arc Welded Ceramics

Zirconium diboride and zirconium carbide‐based ceramics were joined by plasma arc welding to demonstrate the versatility of this technique. A parent material composition consisting of ZrB₂ with 20 vol% ZrC was hot pressed to near full density, sectioned to produce specimens for welding, and welded together to produce billets for mechanical property studies. The four‐point flexure strength of the parent material was ~660 MPa, while the strength of the welded specimens ranged from ~140 to ~250 MPa. Microstructural analysis revealed that decreased strength in the welded specimens was caused by volume flaws, microcracking of large ZrB₂ grains (up to 1 mm in length), and residual tensile stresses that developed at the surface of weld pools during cooling. The versatility of plasma arc welding was demonstrated by joining of ZrC‐based ceramics and fabricating three ZrB₂–ZrC components for potential applications, including a high‐temperature electrical contact, an ultra‐high‐temperature thermocouple, and a wedge that was a notional wing leading edge. These three applications demonstrated the ability to join ceramics to a refractory metal, fabricate a chemically inert high‐temperature thermocouple, and produce complex shapes for aerospace applications.     

Sintering Behavior and Dielectric Properties of Ultra‐Low Temperature Fired Silver Molybdate Ceramics

Ag₂MoO₄ ceramic was prepared by using the solid‐state reaction method, which could be sintered at 450°C for 2 h, having a relative permittivity of 8.08, a Qf value of 17 000 GHz, and a temperature coefficient of resonance frequency about ?133 ppm/°C. Ag₂MoO₄ ceramic was chemically compatible with silver but reacted seriously with aluminum to form (Ag_0.5Al_0.5)MoO₄ during the sintering. The fitting of infrared spectra and the Shannon's additive rule were employed to study intrinsic dielectric behaviors of the ceramics at microwave region. Ionic displacive polarization and the electronic polarization contributed almost equally to the dielectric permittivity of the ceramic at microwave region. The Ag₂MoO₄ ceramics could be a good candidate for ultra‐low temperature co‐fired microwave devices.     

Reproducible X-ray excited luminescence performance with transparent Tb3+-doped NaGd2F7 scintillating glass ceramics

Oxyfluoride glass ceramics with low toxicity, high stability and strong X-ray excited luminescence intensity are introduced as scintillating material. Herein, a series of novel NaGd₂F₇:xTb³⁺ (x = 0, 0.1, 0.2, 0.3, 0.4) were synthesized through in situ growth self-crystallization. X-ray diffraction, fourier transform infrared spectrometer and transmission electron microscopy were measured to investigate the structure and morphology of NaGd₂F₇ glass ceramics. These investigations demonstrate that NaGd₂F₇ nanocrystals are uniformly distributed in glass matrix with 20–30 nm diameter. Photoluminescence and X-ray excitation spectra are greatly enhanced after further thermal treatment which verify better crystallization of NaGd₂F₇ glass ceramics. The X-ray excited luminescence of the GC2–640 sample can reach 143.8% of the commercial BGO. More importantly, the damaged material can be completely repaired by annealing at 350 °C for 30 min. Our investigation indicates that Tb-doped transparent NaGd₂F₇ glass ceramics are potential candidates of X-ray scintillating material.     

Piezoelectric Properties of Lead‐free Piezoelectric Ceramics and Their Energy Harvester Characteristics

The energy convergence efficiency (η) and dimensionless figure of merit (DFOM) of CuO‐added (Na_0.5K_0.5)NbO₃ (CNKN) ceramics are larger than those of NKN ceramics because of their large Q_m values and small dielectric losses. Moreover, the η and DFOM values of CNKN ceramics are comparable to those of P‐5C ceramics, which exhibit the highest η and DFOM. Furthermore, the CNKN harvester exhibits a high power density of 12 mW/cm³ at 93 Hz with a load resistance of 250 kΩ; this is similar to the PZT‐based energy harvester, indicating that the CNKN ceramic is a good candidate material for energy harvesters.     

Influence of calcium doping concentration on the performance of Ce,Ca:LuAG scintillation ceramics

Ce,Ca:LuAG scintillation ceramics with different Ca²⁺ co-doping concentrations were prepared by the solid-state reaction method. The concentration of Ce³⁺ was fixed at 0.3 at% and the concentration of Ca²⁺ ranged from 0 to 1.2 at%. We systematically studied how the Ca²⁺ concentration affects the optical quality of Ce,Ca:LuAG ceramics by influencing the microstructure in the vacuum sintering and HIP post-treatment. Good optical transmittance could be obtained with Ca²⁺ concentrations between 0.05 and 0.8 at%, which reached 76.0–81.9 % at 520 nm. The PL and scintillation decay times decrease with increasing Ca²⁺ concentration up to 0.6 at% with no clear trend above this value. The light yield (LY) values at different shaping times decrease with increasing Ca²⁺ concentration but the fast scintillation component (LY_0.5 μs/ LY_3.0 μs) increases significantly from 79 % to 97 %. The co-doping of Ca²⁺ also reduces the afterglow level by more than one order of magnitude.     

Low‐Temperature Sinterable (1−x)Ba3(VO4)2–xLiMg0.9Zn0.1PO4 Microwave Dielectric Ceramics

The novel low‐temperature sinterable (1 ? x)Ba₃(VO₄)₂–xLiMg_0.9Zn_0.1PO₄ microwave dielectric ceramics were prepared by cofiring the mixtures of pure‐phase Ba₃(VO₄)₂ and LiMg_0.9Zn_0.1PO₄. The phase structure and grain morphology of the ceramics were evaluated using X‐ray diffraction, Raman spectra, and scanning electron microscopy. The results indicated that Ba₃(VO₄)₂ and LiMg_0.9Zn_0.1PO₄ phases can well coexist in the sintered body. Nevertheless, a small amount of LiZnPO₄ and some vanadate phases with low melting points were observed, which not only can influence the microwave dielectric properties of the ceramic but also can obviously improve the densification behavior at a relatively low sintering temperature. The near‐zero temperature coefficients of the resonant frequency (τ_f) could be achieved by adjusting the relative content of the two phases owing to their opposite τ_f values and simultaneously a desirable quality factor Q × f value can be maintained. No chemical reaction between the matrix ceramic phase and Ag took place after sintering at 800°C for 4 h. The ceramics with 45 vol% LiMg_0.9Zn_0.1PO₄ can be well sintered at only 800°C and exhibit excellent microwave dielectric properties of ε_r ~ 10, Q × f ~ 64 500 GHz, and τ_f ~ ?2.1 ppm/°C, thus showing a great potential as a low‐permittivity low‐temperature cofired microwave dielectric material.     

Fabrication and upconversion luminescence properties of Er:SrF2 transparent ceramics compared with Er:CaF2

SrF₂ transparent ceramic is a promising upconversion material due to the low phonon energy. The effect of different sintering temperatures on Er:SrF₂ transparent ceramics was investigated. The suitable sintering temperature for Er:SrF₂ transparent ceramics was 900 °C by hot-pressed sintering in this study. High quality of Er:SrF₂ transparent ceramics with different doping concentrations were obtained. The upconversion luminescence spectra and decay behavior were compared between Er:SrF₂ and Er:CaF₂ transparent ceramics with different Er³⁺ doping concentration. The green emission of 5 at.% Er:SrF₂ ceramic was much stronger than that of 5 at.% Er:CaF₂ ceramic, while the red emission of Er:SrF₂ ceramic was almost the same as that of Er:CaF₂ ceramic. The upconversion luminescence lifetime of Er:SrF₂ transparent ceramics was longer than that of Er:CaF₂.All the results indicated Er:SrF₂ transparent ceramics was a candidate for green fluorescent upconversion materials.     

Elaboration,Structure, and Intense Upconversion in Transparent KYb2F7:Ho3+ Glass‐Ceramics

Novel transparent oxyfluoride glass‐ceramics containing KYb₂F₇:Ho³⁺ nanocrystals were successfully elaborated by melt‐quenching technique with further thermal treatment for the first time. Their structural and luminescent properties were investigated systemically by XRD, HRTEM, absorption spectra, upconversion spectra, and lifetime measurements. Under 980 nm laser excitation, all samples exhibited characteristic emissions of Ho³⁺. Attractively, the upconversion emissions of Ho³⁺, especially green and near‐infrared emissions, were enormously enhanced 190 times after crystallization. The incorporation of Ho³⁺ into KYb₂F₇ nanocrystals with lower phonon energy was responsible for this phenomenon. Our research may enrich the understanding of fluoride‐nanocrystals‐based transparent oxyfluoride glass‐ceramics.     

High Conductivity Electrolyte: Zn2GeO4

Zn₂GeO₄ ceramic materials were synthesized by the solid‐state method. Zn₂GeO₄ powders were investigated with X‐ray powder diffraction (XRD) and high‐resolution transmission electron microscopy (HRTEM). Oxygen defects in the Zn₂GeO₄ ceramics were investigated by photoluminescence, Raman, and EDS spectra. Conductivity of Zn₂GeO₄ was 0.18 S/cm at low temperature of 773 K, and its activation energy was 0.49 eV. The results showed that Zn₂GeO₄ was a promising low‐temperature electrolyte with high conductivity.     

Antiferroelectric‐ferroelectric phase transition in lead‐free AgNbO3 ceramics for energy storage applications

The high‐energy storage density reported in lead‐free AgNbO₃ ceramics makes it a fascinating material for energy storage applications. The phase transition process of AgNbO₃ ceramics plays an important role in its properties and dominates the temperature and electric field dependent behavior. In this work, the phase transition behavior of AgNbO₃ ceramics was investigated by polarization hysteresis and dielectric tunability measurements. It is revealed that the ferrielectric (FIE) phase at room temperature possesses both ferroelectric (FE)‐like and antiferroelectric (AFE)‐like dielectric responses prior to the critical AFE‐FE transition point. A recoverable energy storage density of 2 J/cm³ was achieved at 150 kV/cm due to the AFE‐FE transition. Based on a modified Laudau phenomenological theory, the stabilities among the AFE, FE and FIE phases are discussed, laying a foundation for further optimization of the dielectric properties of AgNbO₃.